Assessment of hairline EEG as a screening tool for nonconvulsive status epilepticus: Response to Bubrick et al

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LETTERS/COMMENTARY

Drug resistance in epilepsy: More twists inthe tale

To the Editor:Resistance to drug treatment is widespread across the

spectrum of human diseases. For any given condition, mul-tiple mechanisms probably contribute to the clinical phe-nomenon of resistance to a single or multiple drugs. Onemechanism that has received extensive attention across dis-eases is that of multidrug transport. Numerous multidrugtransport proteins are known, and share the general abil-ity to transport a variety of drugs, that often have dis-parate chemical structures, against concentration gradients,reducing the desired effects of those drugs. P-glycoproteinis the archetypal example of such a protein, and has beenproposed as a mediator of drug resistance in disparate hu-man conditions including various cancers, infections suchas malaria, inflammatory conditions such as rheumatoidarthritis and Crohn’s disease, and disorders of the cen-tral nervous system. However, progress has proven diffi-cult with results of different studies within the same fieldoften being in conflict. One aspect of P-glycoprotein bi-ology that is both particularly important and especiallycontroversial is the variation in quantity and function ofP-glycoprotein that may be due to inherited variation in theencoding gene, ABCB1. Despite numerous efforts, no clearassociation of ABCB1 genetic variation with clinical phe-notypes has emerged in any disease field.

These issues are well exemplified in the study of theepilepsies. About 30% of patients have epilepsy that provesresistant to treatment with multiple antiepileptic drugs(AEDs), even when AEDs with a range of putative mecha-nisms of action are used in an individual patient. The ideathat P-glycoprotein might mediate at least part of this drugresistance was met with both enthusiasm and skepticism,and as in oncology, initial optimism has been clouded byconflicting results. A study published in 2003 suggestedthat there was an association between the CC major al-lele homozygote at the ABCB1 3435 locus and resistanceto antiepileptic drug treatment (Siddiqui et al., 2003). Anexact replication of this first report failed to confirm theoriginal findings, and concluded that any effect of the 3435polymorphism could only be comparatively modest (Tanet al., 2004). Several other studies have examined the as-sociation between this polymorphism and drug resistancein the epilepsies, but none were structured as a replication

of the original study, differing critically in the phenotypesconsidered. But if P-glycoprotein, and particularly any ge-netically mediated variation in its activity, has any role toplay in drug resistance in the epilepsies, can phenotypicdifferences between studies really explain the failure to ro-bustly identify a role for P-glycoprotein from such geneticassociation studies? If there is a real effect of significance,should it not be obvious even if the studied phenotypes areslightly different?

The latest, and very elegant, analysis of P-glycoproteinfunctional genomics, published this year in Science, maywell provide a basis for understanding some of the lack ofagreement between studies of association between geneticvariation in ABCB1 and the clinical phenotype of drug re-sistance, whether the initially-reported association is real,a false-positive or a cohort-specific effect. Kimchi-Sarfatyet al. show, using a variety of model systems, that ge-netic variation within ABCB1 does affect the structure andtransport function of the encoded P-glycoprotein (Kimchi-Sarfaty et al., 2007). In particular, the authors demonstrateconvincingly and deftly that the transport function of P-glycoprotein not only depends on genotype at specified lociwithin ABCB1, but also, critically, that differences in trans-port function are exaggerated when the transcription ma-chinery is put under stress, for example when it is madeto work harder due to increased gene expression. Thus,the genotype dependence of transport function is exagger-ated under the stimulated state in comparison to the basalor repressed state. In specific experimental models, bothseizures and AED treatment can induce ABCB1 expression,and would therefore be expected to amplify any ABCB1genotype effect on P-glycoprotein quantity and function(Loscher and Potschka, 2005). Therefore, if phenotypesare not matched between studies, for example if one studyfocuses on a cohort with a more severe “drug-resistant”phenotype (in comparison to a control cohort) while an-other study examines a less severe “drug-resistant” cohort,there is good reason to believe that genotype-dependentdifferences should already be expected between thesestudies, in effect stratification biasing the results towardnonreplication from the outset. A biological, rather thana technical, basis for replication failure has thus emerged,emphasizing the importance of matching phenotypesacross studies or cohorts. Notably, environmental factorsbeyond seizures and AED exposure can affect ABCB1 ex-pression, making studies of P-glycoprotein pharmacoge-nomics even more complicated (Kwan and Brodie, 2005).

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The pressing need to demonstrate that P-glycoprotein cantransport AEDs in vivo in humans with epilepsy remains:pharmacogenomics may of course provide surrogateevidence.

Beyond this, the authors show that in fact the con-formation of P-glycoprotein, as reflected in sensitivity totrypsin-digestion, may in fact be altered in the presence ofsubstrate-inhibitors, such as verapamil. This carries furtherimplications, with respect to proposals to inhibit the puta-tive overactivity of P-glycoprotein as a therapeutic strategyin drug-resistant epilepsy. There is some way to go beforea rational strategy can be evolved for application to clinicalpractice.

Kimchi-Sarfaty et al.’s work suggests that the role indrug-resistant epilepsy of genetic variation in ABCB1 bearsreexamination, requiring precisely formulated phenotypesand exact replication studies, in particular with cohortsmatched for the degree of drug resistance. This will requiremore precise definition of resistance to AEDs, and the de-gree of this resistance, than has hitherto been stipulated.Their work also leads to the conclusion that longitudinalstudies of P-glycoprotein function in individual patientsshould be undertaken, with assessment of ABCB1 geneexpression considered in multivariate analyses incorporat-ing measures of seizure activity and AED exposure. Onemight expect that if there are real genotype-dependent dif-ferences in clinical drug responsiveness in epilepsy accord-ing to variation in ABCB1, then these differences will be-come more apparent as some patients with epilepsy clearlydevelop a treatment-resistant phenotype in comparison toother patients who will continue to manifest a more drug-responsive phenotype. Such studies are now necessary inorder to determine definitively whether P-glycoprotein,and particularly whether genetic variation in its encodinggene, underlie drug resistance in human epilepsy. Giventhe pervasive consequences of drug-resistant epilepsy, thispursuit would seem well worthwhile.

The work of Kimchi-Sarfaty et al. highlights the impor-tance in genetic association studies of a clear mechanisticunderstanding of polymorphisms upon which investigatorschoose to focus their attention (either before or after an as-sociation study). More broadly, their work illustrates thecritical importance in any genetic association study of aclear definition of phenotypes, and the rigorous applicationof that phenotype definition in practice.

Sanjay M. Sisodiya1

[email protected] B. Goldstein2

1Department of Clinical and Experimental EpilepsyInstitute of Neurology

UCL, Queen SquareLondon and National Society for Epilepsy

Bucks, United Kingdom

2Institute for Genome Sciences and PolicyCenter for Population Genomics and Pharmacogenetics

Duke University, Durham, NC, U.S.A.

REFERENCES

Kimchi-Sarfaty C, Oh JM, Kim IW, Sauna ZE, Calcagno AM, AmbudkarSV, Gottesman MM. (2007) A “silent” polymorphism in the MDR1gene changes substrate specificity. Science 315:525–528.

Kwan P, Brodie MJ. (2005) Potential role of drug transporters in thepathogenesis of medically intractable epilepsy. Epilepsia 46:224–235.

Loscher W, Potschka H. (2005) Blood-brain barrier active efflux trans-porters: ATP-binding cassette gene family. NeuroRx 2:86–98.

Siddiqui A, Kerb R, Weale ME, Brinkmann U, Smith A, Goldstein DB,Wood NW, Sisodiya SM. (2003) Association of multidrug resistancein epilepsy with a polymorphism in the drug-transporter gene ABCB1.N Engl J Med 348:1442–1448.

Tan NC, Heron SE, Scheffer IE, Pelekanos JT, McMahon JM, Vears DF,Mulley JC, Berkovic SF. (2004) Failure to confirm association of apolymorphism in ABCB1 with multidrug-resistant epilepsy. Neurol-ogy 63:1090–1092.

Drug resistance in epilepsy: Why is a simpleexplanation not enough?

To the Editor:The issue of pharmacoresistance in epilepsy has received

considerable attention in recent years, and the search formechanisms that might explain why around 30% of pa-tients fail to respond to current medications continuesapace. A number of plausible hypotheses have been pro-posed, including inadequate penetration of antiepilepticdrugs (AEDs) across the blood–brain barrier (BBB); ac-quired alterations to the structure and/or functionality ofion channels and neurotransmitter receptors that representthe principal targets of AEDs; and an inherent resistance,governed by genetic variants of proteins involved in thepharmacokinetics and pharmacodynamics of AED action(Schmidt and Loscher, 2005). Of these, the so-called trans-porter hypothesis, which describes the active extrusion ofAEDs from their intended site of action, is the most exten-sively researched and documented.

A number of drug efflux transporters, including P-glycoprotein (Pgp) and multidrug-resistance–associatedproteins (MRPs) are located in the apical membrane ofcapillary endothelial cells that form the BBB; they are be-lieved to act as a physiologic defense mechanism, protect-ing the brain from potentially toxic xenobiotics by limit-ing drug penetration across the BBB (Kwan and Brodie,2005). Pathologically elevated expression of Pgp has beenfound in the region of experimentally induced seizurefoci and in spatial association with a number of clinicalneuropathologies that are associated with uncontrolledseizures (Sisodiya et al., 2002). Experimental and anec-dotal clinical reports have linked overexpression of drug

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transport proteins with acute seizure activity, and a num-ber of AEDs have been mooted as substrates for Pgp orMRPs or both (Loscher and Potschka, 2005). These ob-servations have spawned the multidrug transporter hypoth-esis, which proposes that refractory epilepsy may be theconsequence of a localized overexpression of transporterproteins that prevents AEDs from penetrating the BBBin sufficient concentration—explaining why patients areresistant to multiple AEDs with distinct mechanisms ofaction.

This contemporary theory is founded on three basicpremises: (1) that overexpression of drug transporter pro-teins is exquisitely localized to the site of primary pathol-ogy, preventing AED access to the seizure focus butpermitting drug penetration in other brain areas, as evi-denced by the precipitation of CNS side effects in other-wise drug-resistant patients; (2) that overexpression of drugtransporter proteins is exclusively observed in pharmacore-sistant epilepsy patients and is not an epiphenomenon ofrecurrent seizures or the underlying pathology; and (3) thatthe majority of (if not all) currently available AEDs aresubstrates for active efflux by one or more drug transportproteins.

Another potentially important issue is whether theproposed overexpression of drug transporter proteins isintrinsic (constitutive) or acquired as a consequence ofthe disease, uncontrolled seizures, chronic treatment withAEDs, or a combination of these factors. It is generallybelieved that the expression and functionality of Pgp canbe influenced by polymorphisms in the encoding gene(ABCB1; Hoffmeyer et al., 2000). If so, these variantsmay be an important contributor to the pharmacoresis-tant epilepsy phenotype, or at least a surrogate markerof it.

One of the most widely recognized single nucleotidepolymorphisms (SNPs) in the human ABCB1 gene is the Cto T transformation at position 3435 of exon 26 (Hoffmeyeret al., 2000). An initial study by Sisodiya’s group (Siddiquiet al., 2003) suggested that the homozygous C-variant,which is associated with higher expression and increasedactivity of Pgp, is more common in patients with pharma-coresistant epilepsy. This would fit with the hypothesis thatelevated Pgp decreases drug responsiveness. However, sev-eral subsequent investigations, including one direct repli-cation, failed to confirm the original observation (Tanet al., 2004; Sills et al., 2005). It has been argued that dif-ferences in the definition of responsiveness can account forthis disparity in the results of ABCB1 association studies.While this is possible, it seems unlikely given the extremediscordance in findings and limited potential for entirelymisclassifying sufficient numbers of patients. In their com-mentary, Sisodiya and Goldstein (2007) accept that subtlephenotypic differences may be less important than previ-ously thought. Instead, they choose to discuss the recent

data of Kimchi-Sarfaty and colleagues (2007) and suggestthat the discrepancy in the findings of ABCB1 associationstudies lies in the degree of refractoriness and how thatmight vary between individual patient cohorts. Again, thisis possible but even further removed from more obviousexplanations.

The major weakness of all such association studies ofthe ABCB1 gene in epilepsy, and the multidrug transporterhypothesis in general, is the current lack of evidence to sug-gest that AEDs are substrates for Pgp or indeed any otherhuman efflux transporter. As discussed earlier, if these pro-teins have functional and clinical relevance to the phe-nomenon of pharmacoresistant epilepsy, then the majorityof (if not all) AEDs must be substrates for one or moretransport systems. This fundamental premise has been as-sessed in a series of investigations employing a varietyof techniques and models. Initial studies in experimentalanimals suggested that several commonly used AEDs aretransported to some extent by both Pgp and MRPs (Loscherand Potschka, 2005). This led to the somewhat prema-ture assumption that drug efflux is promiscuous, species-independent, and of sufficient capacity to be nonsaturableat clinically relevant concentrations.

However, more recent in vitro experiments employingtransfected cell lines overexpressing rodent and human ef-flux transporters have cast doubt on this notion. One se-ries of experiments demonstrated transport of phenytoinand levetiracetam in cells overexpressing mouse but nothuman Pgp, there was no discernible transport of carba-mazepine or valproate in cells transfected with Pgp fromeither species, and no interaction of any AED with hu-man MRP1 or MRP2 (Baltes et al., 2007a, 2007b). Afurther study failed to demonstrate any efflux of pheny-toin, carbamazepine, phenobarbital, ethosuximide, lamot-rigine, vigabatrin, gabapentin, or topiramate from cells ex-pressing the human form of Pgp (Crowe and Teoh, 2006).These data suggest that species differences in the trans-port of AEDs by Pgp are greater than previously antici-pated and that direct extrapolation of efflux transport datafrom rodent-based models to the clinical arena may bemisleading.

The apparent lack of transport of any major AED byhuman Pgp would strongly suggest that the originally re-ported association between resistance to AED treatmentand the homozygous C-variant at the 3435 locus on ABCB1may have arisen by chance. This would explain why sev-eral subsequent investigations failed to replicate this ob-servation and obviates the need for further dissection ofthe discrepancy. To propose additional association studiesemploying more highly restricted phenotypic definitionsin a subjective and heterogeneous disorder like epilepsyis unrealistic, and there is certainly no need to go as faras considering the influence of previously unsuspectedtranscriptional stresses on protein function, at least not in

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this case. If human efflux transporters do not transportAEDs, then it is reasonable to conclude that overexpres-sion of Pgp in the BBB of pharmacoresistant epilepsy pa-tients, whether constitutive or acquired, may be nothingmore than an epiphenomenon related to the frequency ofseizures and/or underlying pathology and one which is de-void of functional consequences for brain drug concentra-tions and the efficacy of AEDs.

Wolfgang Loscher1

[email protected] J. Sills2

1Department of PharmacologyToxicology and Pharmacy

University of Veterinary MedicineHannover, Germany

Center for Systems NeuroscienceHannover, Germany

Epilepsy Unit2Section of Clinical Pharmacology & Stroke Medicine

University Division of Cardiovascular &Medical Sciences

Western Infirmary, Glasgow, Scotland

REFERENCES

Baltes S, Fedrowitz M, Luna Tortos C, Potschka H, Loscher W. (2007a)Valproic acid is not a substrate for P-glycoprotein or multidrug resis-tance proteins 1 and 2 in a number of in vitro and in vivo transportassays. J Pharmacol Exp Ther 320:331–343.

Baltes S, Gastens AM, Fedrowitz M, Potschka H, Kaever V, LoscherW. (2007b) Differences in the transport of the antiepileptic drugsphenytoin, levetiracetam and carbamazepine by human and mouse P-glycoprotein. Neuropharmacology 52:333–346.

Crowe A, Teoh Y-K. (2006) Limited P-glycoprotein mediated efflux foranti-epileptic drugs. J Drug Targeting 14:291–300.

Hoffmeyer S, Burk O, von Richter O, Arnold HP, Brockmoller J, Johne A,Cascorbi I, Gerloff T, Roots I, Eichelbaum M, Brinkmann U. (2000)Functional polymorphisms of the human multidrug-resistance gene:multiple sequence variations and correlation of one allele with P-glycoprotein expression and activity in vivo. Proc Natl Acad Sci US A 97:3473–3478.

Kimchi-Sarfaty C, Oh JM, Kim I-W, Sauna ZE, Calcagno AM, AmbudkarSV, Gottesman MM. (2007) A ‘silent’ polymorphism in the MDR1gene changes substrate specificity. Science 315:525–528.

Kwan P, Brodie MJ. (2005) Potential role of drug transporters in thepathogenesis of medically intractable epilepsy. Epilepsia 46:224–235.

Loscher W, Potschka H. (2005) Drug resistance in brain diseases and therole of drug efflux transporters. Nat Rev Neurosci 6:591–602.

Schmidt D, Loscher W. (2005) Drug resistance in epilepsy: putative neu-robiologic and clinical mechanisms. Epilepsia 46:858–877.

Siddiqui A, Kerb R, Weale ME, Brinkmann U, Smith A, Goldstein DB,Wood NW, Sisodiya SM. (2003) Association of multidrug resistancein epilepsy with a polymorphism in the drug-transporter gene ABCB1.New Engl J Med 348:1442–1448.

Sills GJ, Mohanraj R, Butler E, McCrindle S, Collier L, Wilson EA,Brodie MJ. (2005) Lack of association between the C3435T polymor-phism in the human multidrug resistance (MDR1) gene and responseto antiepileptic drug treatment. Epilepsia 46:643–647.

Sisodiya SM, Lin W-R, Harding BN, Squier MV, Thom M. (2002) Drugresistance in epilepsy: expression of drug resistance proteins in com-mon causes of refractory epilepsy. Brain 125:22–31.

Sisodiya SM, Goldstein DB. (2007) Drug resistance in epilepsy: moretwists in the tale. Epilepsia in press.

Tan NCK, Heron SE, Scheffer IE, Pelekanos JT, McMahon JM, VearsDF, Mulley JC, Berkovic SF. (2004) Failure to confirm association ofa polymorphism in ABCB1 with multidrug-resistant epilepsy. Neurol-ogy 63:1090–1092.

Where is the evidence that p-glycoproteinlimits brain uptake of antiepileptic drug and

contributes to drug resistance in epilepsy?

To the Editors:The article by Sisodiya and Goldstein provides an in-

teresting and novel perspective on the current debate overthe role of p-glycoprotein (Pgp), or lack thereof, in mul-tidrug resistance in epilepsy. The authors point to a recentreport showing that a synonymous single nucleotide poly-morphism (i.e., a so-called silent mutation) at the 3435 lo-cus of the multidrug resistant 1 (MDR1 or ABCB1) genealters Pgp conformation and its interaction with drug sub-strates and inhibitors, while expression levels of mRNAand protein remain the same (Kimchi-Sarfaty et al., 2007).The synonymous mutation apparently affects the timingof cotranslational folding of Pgp. Based on this postulate,Sisodiya and Goldstein suggest that the functional impactof ABCB1 genotype variation, at least at the 3435 locus,is magnified or becomes apparent when the transcriptionalmachinery is under stress. They then surmised that sever-ity of “drug-resistance” phenotype (i.e., the demand placedon ABCB1 translation if upregulation of ABCB1 transcrip-tion were to occur at the brain capillary endothelium inresponse to the epileptogenic process or seizure activity)may be an overlooked variable in previous investigationson the possible role of Pgp in rendering resistance to mul-tiple antiepileptic drugs (AEDs). Lack of clear definitionand classification of drug-resistance phenotype might haveaccounted for the discrepancies in the studies of P-pg anddrug resistant epilepsy.

We agree that differences in the drug-resistance phe-notypes between earlier clinical studies may have beena confounding variable; however, a more basic issue isthe lack of convincing evidence that (1) AEDs are high-affinity substrates of Pgp and (2) the uptake of the AEDsacross the blood–brain barrier (BBB) is dependent on Pgp,especially in cases of apparent drug resistance. There issignificant disagreement in the literature as to whetheror not AEDs are all Pgp substrates. Recently, Baltes etal. (2007) demonstrated significant differences in the ef-flux transport of several AEDs by Pgp between species,and raised the question of whether functional differencescould exist even between tissue types that express Pgp.This suggests caution in extrapolating experimental data

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gathered in animal models to human epilepsies. Over-all, the available data in the literature indicate that AEDsare either not substrates or at best very weak substratesof Pgp. One way to illustrate to the relative impact ofPgp on drug uptake into the brain is to compare the re-ported effects of selective Pgp inhibitors (verapamil, PSC-833) on the brain-to-plasma or microdialysate-to-plasmaratio for AEDs and classic Pgp substrates, namely, vin-cristine, cyclosporine, and digoxin. For vincristine, Pgp in-hibition resulted in a 9-fold increase in brain uptake (Drionet al., 1996). In comparison, Pgp inhibition only increasedphenytoin, carbamazepine, phenobarbital, lamotrigine, andfelbamate, 0.5- to 1.1-fold over baseline (Potschka andLoscher 2001; Potschka et al., 2001, 2002). In the ABCB1aknockout mouse model, vinblastine, cyclosporine, anddigoxin brain uptake increased 20- to 50-fold (Schinkelet al., 1994; Schinkel et al., 1995). In comparison, therewas only a 2-fold increase for topiramate, and no in-crease in brain uptake for phenytoin, phenobarbital, car-bamazepine, or lamotrigine (Sills et al., 2002). Therefore,the effect of Pgp on the brain uptake of AEDs is barelymeasurable, and certainly much weaker than the classicPgp substrates. This fact, coupled with the recognitionthat all AEDs are lipophilic and have good to excellentpassive permeability across cell barriers, would predicta minimal to negligible role for Pgp-mediated efflux onthe net uptake of AEDs into the brain, at least into nor-mal or nonepileptic areas. This leaves only the possibil-ity that Pgp might assume greater importance at epilep-tic loci where upregulation of ABCB1 transcription hasbeen demonstrated, possibly as a result of transcriptionalactivation by the localized pathology. There is one study,reporting of an inverse linear correlations between 10-hydroxy-10,11-dihydrocarbazepine brain-to-plasma con-centration ratio and ABCB1 expression in eight drug resis-tant patients (Marchi et al., 2005). However, direct proof ofcausal relationship between upregulation of efflux trans-porter and decrease in AED uptake into epileptic com-pared to nonepileptic loci in a patient population withcarefully documented refractoriness to AED therapy is notavailable.

A further argument for the lack of any evidence for ac-tive efflux process for AEDs at the brain is the notableabsence of saturable transport. Protein-mediated transporthas the hallmark of exhibiting saturation kinetics; thisis certainly a reported phenomenon for Pgp-mediatedefflux transport at the intestinal epithelium (Harrisonet al., 2004 and others). In the case of saturable Pgp-mediated efflux at the BBB, one would expect a non-linear brain-to-plasma concentration relationship; that is,a more than proportionate increase in brain concentra-tion with an increase in plasma concentration at highdoses. For phenytoin, phenobarbital, and carbamazepine,there is ample clinical data demonstrating a linear rela-tionship between their brain concentrations and unbound

drug serum concentrations (Sherwin et al., 1973; Vajdaet al., 1974; Houghton et al., 1975; Harvey et al., 1977;Paulson et al., 1982; Onishi et al., 1984; Friel et al., 1989;Rambeck et al., 1993, Scheyer et al., 1994a, 1994b; Schn-abel et al., 1994). Similar linear concentration relation-ships have been observed with brain microdialysis datafrom patients undergoing surgical treatment of drug re-sistant epilepsy. These studies covered a wide range ofAED doses and concentrations with little if any hint ofsaturation kinetics suggestive of protein-mediated trans-port processes. It should be noted that the majority ofthese brain distribution studies were conducted in patientswith drug-resistant epilepsy, where purportedly increasedexpression of ABCB1 and other ABC-transporters couldoccur.

Despite the intriguing data from experimental studies invitro and in animal models, at present there is no com-pelling clinical evidence that Pgp at the BBB is limitingthe uptake of AEDs into the brain of epileptic patientsand contributes to the drug-resistance phenotype. The ab-sence of evidence should not dissuade us from exploringthe possibility that ABCB1 upregulation or its genetic poly-morphism could still be a one of several causal mecha-nisms of drug resistance epilepsy; it does, however, callfor some caution in accepting this seemingly plausibleand attractive hypothesis at the neglect of other possiblemechanisms.

Gail D. Anderson1

[email protected] D.Shen1,2

1Department of PharmacyUniversity of Washington, Seattle, WA, U.S.A.

2Clinical Research DivisionFred Hutchinson Cancer Research Center

Seattle, WA, U.S.A.

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Baltes S, Gastens AM, Fedrowitz M, Potschka H, Kaever V, LoscherW. (2007) Differences in the transport of the antiepileptic drugsphenytoin, levetiracetam and carbamazepine by human and mouse P-glycoprotein. Neuropharmacology 52:333–346.

Drion N, Lemaire M, Lefauconnier JM, Scherrmann JM. (1996) Role ofP-glycoprotein in the blood-brain transport of colchicine and vinblas-tine. J Neurochem 67:1688–1693.

Friel PN, Ojemann GA, Rapport RL, Levy RH, Van Belle G. (1989)Human brain phenytoin: correlation with unbound and total serumconcentrations. Epilepsy Res 3:82–85.

Harrison A, Betts A, Fenner K, Beaumont K, Edgington A,Roffey S, Davis J, Comby P, Morgan P. (2004) Nonlin-ear oral pharmacokinetics of the alpha-antagonist 4-amino-5-(4-fluorophenyl)-6,7-dimethoxy-2-[4-(morpholinocarbonyl)-perhydr o-1,4-diazepin-1-yl]quinoline in humans: use of preclinical datato rationalize clinical observations. Drug Metab Dispos 32:197–204.

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Harvey CD, Sherwin AL, Van Der Kleijn E. (1977) Distribution of an-ticonvulsant drugs in gray and white matter of human brain. Can JNeurol Sci 4:89–92.

Houghton GW, Richens A, Toseland PA, Davidson SF, M A. (1975) Brainconcentrations of phenytoin, phenobarbital and primidone in epilepticpatients. Eur J Clin Pharmacol 9:73–78.

Kimchi-Sarfaty C, Oh JM, Kim IW, Sauna ZE, Calcagno AM, AmbudkarSV, Gottesman MM. (2007) A “silent” polymorphism in the MDR1gene changes substrate specificity. Science 315:525–528.

Marchi N, Guiso G, Rizzi M, Pirker S, Novak K, Czech T, Baum-gartner C, Janigro D, Caccia S, Vezzani A. (2005) A pilotstudy on brain-to-plasma partition of 10,11-dyhydro-10-hydroxy-5H-dibenzo(b,f)azepine-5-carboxamide and MDR1 brain expression inepilepsy patients not responding to oxcarbazepine. Epilepsia 46:1613–1619.

Onishi S, Ohki Y, Nishimura Y, Itoh S, Isobe K, Hosoe A, YamamotoT, Yamakawa T. (1984) Distribution of phenobarbital in serum, brainand other organs from pediatric patients. Dev Pharmacol Ther 7:153–159.

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Potschka H, Loscher W. (2001) In vivo evidence for P-glycoprotein-mediated transport of phenytoin at the blood-brain barrier of rats.Epilepsia 42:1231–1240.

Potschka H, Fedrowitz M, Loscher W. (2001) P-glycoprotein and mul-tidrug resistance-associated protein are involved in the regulation ofextracellular levels of the major antiepileptic drug carbamazepine inthe brain. Neuroreport 12:3557–3560.

Potschka H, Fedrowitz M, Loscher W. (2002) P-Glycoprotein-mediatedefflux of phenobarbital, lamotrigine, and felbamate at the blood-brainbarrier: evidence from microdialysis experiments in rats. NeurosciLett 327:173–176.

Rambeck B, Schnabel R, May T, Jurgens U, Villagran R. (1993)Postmortem concentrations of phenobarbital, carbamazepine, and itsmetabolite carbamazepine-10,11-epoxide in different regions of thebrain and in serum: analysis of autoptic specimens from 51 epilepticpatients. Ther Drug Monit 15:91–98.

Scheyer RD, During MJ, Hochholzer JM, Spencer DD, Cramer JA, Matt-son RH. (1994a) Phenytoin concentrations in the human brain: an invivo microdialysis study. Epilepsy Res 18:227–232.

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Schinkel AH, Smit JJ, van Tellingen O, Beijnen JH, Wagenaar E, vanDeemter L, Mol CAAM, van der Valk MA, Robanus-Maandag EC,te Riele HPJ, Berns AJM, Borst P. (1994) Disruption of the mousemdr1a P-glycoprotein gene leads to a deficiency in the blood-brainbarrier and to increased sensitivity to drugs. Cell 77:491–502.

Schinkel AH, Wagenaar E, van Deemter L, Mol CA, Borst P. (1995) Ab-sence of the mdr1a P-Glycoprotein in mice affects tissue distributionand pharmacokinetics of dexamethasone, digoxin, and cyclosporin A.J Clin Invest 96:1698–1705.

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Assessment of hairline EEG as a screeningtool for nonconvulsive status epilepticus

To the Editor:Kolls and Husain (2007) attempted to address the impor-

tant question of whether an electroencephalogram (EEG)using an abbreviated electrode array, such as that devisedby Bridgers and Ebersole (1988), is sufficiently sensitive touse in emergency evaluation of patients for nonconvulsivestatus epilepticus (NCSE). They concluded that it is not so,and recommended against further pursuit of this method.We have several criticisms of this study, particularly of theconclusions.

First, despite the title of their study, the authors exam-ined only how consistently a variety of EEG findings wereidentified on reformatted, limited montages. With regardto seizure detection, their reported sensitivities (72–85%,the lower figure reflecting unanimity among all 5 readers)were actually comparable to other commonly used tests. Alonger sampling time and knowledge of the clinical situ-ation would likely contribute to even better performance,given multiple seizures are typically recorded in NCSE,facilitating recognition of ictal patterns. Furthermore, anEEG is not a “screening tool,” a procedure typically per-formed on a large population for detecting disease, butrather a diagnostic test, one that should be performed whenthe clinical suspicion and pretest probability are relativelyhigh. No test with less than 100% sensitivity can entirely“rule out” any condition. It is inappropriate, however, tocompletely dismiss the utility of this test, especially in theright clinical setting. Furthermore, the potential to misin-terpret benign patterns was overemphasized in the authors’discussion, when in fact their data show the test actuallyhad very high specificities (up to 99%), making false posi-tives unlikely.

Diagnosing seizures on a hairline EEG may save valu-able time. If not performed when NCSE is first suspected,alternatives include waiting until a full EEG can be ob-tained (which may be several hours to days), or transfer-ring the patient to another institution. Even when an EEGtechnologist is on call for emergency studies, response ortravel time may contribute to further delays.

At our institution, we systematically train neurology res-idents to perform and interpret hairline EEGs, and have aneurophysiologist available to discuss the results if needed.Many have successfully performed this fast, easy and non-invasive procedure when an EEG technologist was notavailable, and this has been shown to guide management(Milligan and Bromfield, 2005). In addition, it is both ed-ucational and empowering for housestaff to do this. FullEEGs are performed as soon as a technologist is available,typically within hours.

In summary, it is both misleading and potentially dan-gerous to recommend against the use of a test whose

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results may significantly change management of seriouslyill patients, especially when no other viable option may beavailable. More investigation, particularly of the actual re-sults of hairline or other emergency approaches to EEG, isneeded.

Ellen J. [email protected] A. DworetzkyEdward B. Bromfield

Division of Epilepsy, EEG, and Sleep NeurologyDepartment of Neurology

Brigham and Women’s HospitalHarvard Medical School

Boston, MA, USA

REFERENCES

Bridgers SL, Ebersole JS. (1988) EEG outside the hairline: detection ofepileptiform abnormalities. Neurology. 38:146–149.

Kolls BJ, Husain AM. (2007) Assessment of hairline EEG as a screeningtool for nonconvulsive status epilepticus. Epilepsia. 48(5):959–965.

Milligan TA, Bromfield EB. (2005) A Case of “Migralepsy.” Epilepsia.46(Suppl 10):2–6.

Assessment of hairline EEG as a screeningtool for nonconvulsive status epilepticus:

Response to Bubrick et al.

To the Editors:We thank Dr. Bubrick and her colleagues for interest

in our paper. In their letter to Epilepsia (Bubrick et al.,2007), they raise some interesting points for discussion.Overall, they disagree with our conclusions because theyfeel the sensitivity and specificity for detection of noncon-vulsive status epilepticus (NCSE) with a hairline electroen-cephalogram (EEG) is adequate, and that waiting to obtaina standard EEG will needlessly delay treatment decisions.Moreover, they routinely use this practice and have foundit useful (Milligan & Bromfield, 2005).

Since the impetus for our study was the delay in obtain-ing urgent and emergent EEG, we agree that a more rapidassessment would be preferable. Bubrick et al. suggest thatthe sensitivity and specificity of hairline EEG is adequatefor this purpose. In our study, the sensitivity for detectingelectrographic seizures was 72% and for periodic lateral-ized epileptiform discharges (PLED) was only 54% (Kolls& Husain, 2007). Certainly the detection of PLED is veryimportant, since in certain situations it may represent an ic-tal or interictal pattern. Additionally, a review of the misin-terpretations reveals that 33 seizure and 42 PLED patternswere misinterpreted as diffuse slowing (see Figs 3 and 4in Kolls & Husain, 2007). Moreover, seven patterns with

diffuse slowing were misinterpreted as seizures, PLED,or generalized periodic epileptiform discharges (GPED).These are significant errors that may gravely impact patientcare. It should also be noted that samples in our study wereinterpreted by experience neurophysiologists; interpreta-tion by neurology residents resulted in even lower sensi-tivities and specificities (unpublished data). Consequently,we maintain that a hairline EEG is inadequate for diagnos-ing NCSE.

Bubrick et al. note that patterns of NCSE were not stud-ied. The patterns that were selected, such as electrographicseizures, PLED, and GPED, were not random, and are verylikely to be present in patients in NCSE. Identification ofthese patterns would warrant an emergent EEG and pos-sibly treatment of NCSE. Knowledge of the clinical sit-uation, while always helpful, would be only of marginaladditional utility.

Bubrick et al. also noted that they have taught the hair-line EEG technique to their residents and have found it use-ful (Milligan & Bromfield, 2005). Unfortunately, the refer-ence cited to support this claim of usefulness includes asingle patient who was found to be in NCSE with a hair-line EEG. We do not dispute that for the occasional patient,hairline EEG may reveal the correct diagnosis. However,anecdotal studies and case reports cannot establish the util-ity of this technique. Indeed, it was our belief that this tech-nique would be adequate for and expedite the diagnosis ofNCSE, However, our data has shown otherwise. Bubricket al. are encouraged to evaluate their data in a prospectivemanner and publish their results.

Emergent EEG is time consuming and not universallyavailable. Though quicker and easier to obtain, hairlineEEG does not appear to be an adequate substitute. Furtherresearch on this and other alternatives is needed to deter-mine the best method for quickly and accurately determin-ing whether a patient is in NCSE.

1Bradley J. Kolls1,2Aatif M. Husain

[email protected] of Medicine (Neurology)

Duke University Medical Centerand 2Neurodiagnostic Center

Veterans Affairs Medical Center, Durham, NC

REFERENCES

Bubrick EJ, Dworestzky BA, Bromfield EB. (2007) Assessment of Hair-line EEG as a Screening Tool for Nonconvulsive Status Epilepticus(Letter to the Editors). Epilepsia 48:2374–2375.

Kolls BJ, Husain AM. (2007) Assessment of hairline EEG as a screeningtool for nonconvulsive status epilepticus. Epilepsia 48:959–965.

Milligan TA, Bromfield EJ. (2005) A case of “migralepsy.” Epilepsia46(Suppl 10):2–6.

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NEXT MONTH IN Epilepsia

Volume 49 of Epilepsia opens with Dr. Daniel Lowen-stein’s lecture on “Pathways to discovery in epilepsy re-search” (the 2006 Hoyer Lecture at the Annual Meeting ofthe American Epilepsy Society). This January issue alsofeatures a review on “Mechanisms of epileptogenesis intuberous sclerosis complex and related malformations ofcortical development with abnormal glioneuronal prolif-eration” (Dr. Michael Wong). The Full-Length and Briefresearch reports include studies on localization of abnor-mal/epileptic cortex (language testing, intraoperative ultra-sound, MRI and MRS) and on surgical removal of epilep-tic brain (surgery in early life, amygdalohippocampectomy,lateral-to-mesial tissue involvement in TLE). The surgicalset of papers is punctuated by a special ILAE Commis-sion report on “Defining the spectrum of international prac-tice in pediatric epilepsy surgery patients.” Other topics in-cluded in this issue include range from “epileptic automa-tisms in the criminal courts” to “gender differences in bonemineral density” to ”motor cortical exitability in patientswith poststroke epilepsy.”

ONLINE EARLYAsadi-Pooya and Sperling, “Strategies for surgical treat-

ment of epilepsies in developing countries”Goda et al., “Glutamate and dopamine receptors con-

tribute to the lateral spread of epileptiform discharges inrat neocortical slices”

Helmstaedter et al., “Differential effects of temporalpole resection with amygdalohippocampectomy versus se-lective amygdalohippocampectomy on material-specificmemory in patients with mesial temporal lobe epilepsy”

Lee et al., “A new animal model of infantile spasms withunprovoked persistent seizures”

Martin and Kapur, “A combination of ketamine and di-azepam synergistically controls refractory status epilepti-cus induced by cholinergic stimulation”

Plummer et al., “EEG source localization in focalepilepsy: Where are we now?”

Raffo et al., “Calorie-restricted ketogenic diet increasesthresholds to all patterns of pentylenetetrazol-inducedseizures: Critical importance of electroclinical assessment”

Samuels et al., “Herbal medicine and epilepsy: Procon-vulsive effects and interactions with antiepileptic drugs”

Yogarajah and Duncan, “Diffusion-based magnetic res-onance imaging and tractography in epilepsy”

ANNOUNCEMENTS

International symposium on dietary therapiesfor epilepsy and other neurological disorders

This international symposium will take place April 2–5, 2008, at the Ritz-Carlton Hotel in Phoenix, Arizona(U.S.A.). The fundamental goals of this symposium areto share up-to-date information on the rapidly expandingtopic of dietary therapies for epilepsy, and to define the im-portant clinical and research questions that should be pur-sued in the future. The meeting is aimed at a broad rangeof health professionals, including neurologists, epileptol-ogists, research scientists, nurses, and dietitians. Prospec-tive attendees can submit abstracts for poster presentations(deadline is January 15, 2008) to [email protected] limited number of partial travel scholarships are offeredfor junior investigators.

The Symposium will be hosted by the Barrow Neu-rological Institute at St. Joseph’s Hospital & MedicalCenter. Cochairs are Jong M. Rho, Carl E. Stafstrom,and Beth Zupec-Kania. The meeting is sponsored bythe Charlie Foundation, Citizens United for Research inEpilepsy, and Nutricia N.A. For additional information,email Lindsey Kerby at [email protected] or seehttp://www.thebarrow.org/conferences. To register online,go to http://www.peopleware.net/2836.

International symposium on febrile seizuresand related conditions

The Infantile Seizure Society (ISS – Chair, YukioFukuyama) will host the International Symposium onFebrile Seizures and Related Conditions (ISFS – Presi-dent, Yoshihiro Takeuchi) in Otsu, Japan on April 10–11, 2008. Febrile seizures are the most common types ofseizures experienced by infants and young children. How-ever, many questions in both the basic and the clinical are-nas still remain unresolved. The ISFS aims to present acomprehensive update of the topic, and will include dis-cussions on such issues as genetics, epidemiology, patho-physiology, imaging, treatment, education, and subsequentrelated conditions (including epilepsy and mesial tempo-ral sclerosis). This Symposium represents the 11th An-nual Meeting of the ISS. For additional information seethe symposium website at: http://www.iss-jpn.info/ or sendan e-mail to Tomoyuki Takano, secretary of the ISFS, at:[email protected]

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7th Asian & Oceanian Epilepsy Congress

The 7th Asian & Oceanian Epilepsy Congress (AOEC)will take place in beautiful Xiamen on the southeast coastof China, May 15–18, 2008. The Scientific Program willinclude main sessions, and post main sessions mixed withinteresting parallel sessions and platform sessions. The ab-stract submission deadline is January 15, 2008. The earlyregistration deadline is February 15, 2008. For more infor-mation go to: http://www.epilepsyxiamen2008.org/

18th Meeting of the European NeurologicalSociety

The 18th meeting of the European Neurological Soci-ety will take place at the Palais des Congres et des Expo-

sitions, Nice Acropolis, in Nice, France June 7–11, 2008.The deadline for abstract submission is 31 January 2008.Abstracts may only be submitted online at the congresswebsite (http://www.ensinfo.com) and further details willbe available in the fall of 2007.

8th European Congress on Epileptology

The 8th European Congress on Epileptology will takeplace in Berlin, Germany, September 21–25, 2008. It ispresented under the auspices of the German and IsraeliILAE chapters. The online abstract submission system willbe available late in December 2007. The abstract submis-sion deadline is 14th March 2008. For more information goto: http://www.epilepsyberlin2008.org/.

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CALENDAR OF MEETINGS

February 2008

❑ II Latin-American Summer School on Epilepsy(LASSE II)

7–17 FebruarySao Paulo, Brazilhttp://www.lasse.med.br

April 2008

❑ International Symposium on Dietary Therapiesfor Epilepsy and Other Neurological Disorders

2–5 AprilPhoenix, Arizona, U.S.A.http://www.thebarrow.org/conferences

❑ International Symposium on Febrile Seizures andRelated Conditions

10–11 AprilOtsu, Japanhttp://www.iss-jpn.info

May 2008

❑ 7th Asian & Oceanian Epilepsy Congress15–18 MayXiamen, Chinahttp://www.epilepsyxiamen2008.org

June 2008

❑ 18th Meeting of the European NeurologicalSociety

7–11 JuneNice, Francehttp://www.ensinfo.com

August 2008

❑ Venice Epilepsy Summer School, 7thInternational Course: Bridging Basic withClinical Epileptology - 3

AugustVenice, Italye-mail: [email protected]

September 2008

❑ 8th European Congress on Epilepsy21–25 SeptemberBerlin, Germanyhttp://www.epilepsyberlin2008.org

October 2008

❑ 11th European Conference on Epilepsy & Society15–17 OctoberMarseille, Francehttp://www.epilepsyandsociety.org/

November 2008

❑ 5th Congreso Latinoamericano de Epilepsia(ILAE & IBE)

5–8 NovemberMontevideo, Uruguayhttp://www.epilepsymontevideo2008.org

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