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or in combinarion, may produce a simi-lar clinicalpicture. Some characreristics,as described below,are considered help-ful in the differentialdiagnosis, althoughthere is no pathognomonic clinical or. . .ImagIng sIgn.

The gait abnormality in INPH isof frontaldysequilibrium or frontal gaitdisorder type.The most common symp-tomsdescribedby patients areimbalance,tirednessoflegs, legweaknessand, asthedisease progresses, shorter steps, shuf-fling, scuffing and slow turning. 1,2,3Atriad of hypokinetic gait, associatedwitha wide base, decreased step height anddisturbance of dynamic equilibrium isconsidered characteristic ofINPH. 13

The differentiation between INPHand Parkinson's diseasecan be challeng-ing. According to one study, in INPHthe most helpful gait parameters are thewide-based gait, with outward feet rota-tion, decreased range of motion of thelowerextremities,with little or no reduc-tion ofarm swing. In contrast, PD usu-ally has associated extrapyramidalfeatures and the patients respond to vi-sual and acoustic cues. 13

Cortical features such as apraxia,agnosia and aphasia are absent in INPH.Problemswith attention, concentration,forgetfulness, apathy and mental slow-ingarethe rule.Neuropsychologicaltests,although helpful in characterizing thedeficit, are not good predictors of shunt-ing outcome, and in most studies theimprovement in extended neuropsycho-logical batteries isminimal. 14Iddon et al demonstrated theunpredictabilityof the cognitiveresponseto shunt. 15In this study they evaluated11 patients with INPH, 5 in the de-mented range (mini-mental state exami-nation-MMSE24. After shunting, the de-mented patients demonstrated signifi-cant improvement in their MMSE andthe Kendrick Object Learning Test(KOLT) which assessesrecall of every-day objects after a brief presentation pe-riod of a black-and-white illustration ofthem scores.On the other hand, the non-demented patients demonstrated decre sedverbal fluency, impaired spatialrecognition and attentional set shiftingtask. Even though the subjects demon-strated improvement of gait after shunt-

ing, the impairment on tests sensitivetofrontal dysfunction remained.

Urinaty urgency is common in theearlier stages;incontinence isa later sign.7 Urodynamic studies demonstrate hy-perreflexia and instability of the bladderdetrusor muscle, but there isno evidenceof defectivebladder control.This suggestsdamage in the periventricular pathwaysto the sacralbladder centerand decreasedinhibition of bladder contractions.

IDIOPATHICNORMAL PRESSURE

HYDROCEPHALUSIS AN

OVERESTIMA TEDUNCOMMON

DISORDER WITH ACOMMON CLINICAL

TRIAD IN THEELDERLY

POPULATION

The diagnosis of INPH relies onclinical criteria, neuro-imaging evidenceof hydrocephalus and ideallyevidence ofabnormalities in CSF hydrodynamics.Vanneste et al evaluated the predictivevalue of clinical criteria and CT in thediagnosis of INPH. 16By using strictlyclinical (predominant gait disturbance,absent to mild cognitive deficit) and CTcriteria (rounded frontal horns, moder-ate ventriculomegaly, absence of whitematter diseaseand cortical atrophy), thepositive predictive value (PPV) was65 , and the negative predictive value(NPV) was 76 . Ineffective shuntingwas observed in 11 of the patients,while missed improvement occurred in13 . More liberal criteria would haveresulted in a PPV of 58 , ineffectiveshunting in 37 and missed improve-ment in 5 of the patients. The authorsconcluded that clinicalcriteria associatedwith appropriate neuroimaging is thestandard by which new diagnostic test-ing should be used to improve diagnos-tic accuracy and shunt responsiveness.

CSF drainage by lumbar puncture,often considered a goldstandard in thediagnosis ofINPH, has a vety high inci-dence of false negatives; and a prospec-tivestudy failedto provide anysignificantadditional information compared to con-servative clinical and neuroimaging cri-teria were utilized to select patients forshunting. 17Continuous CSF drainageposes a similar problem. In addition, itrequires hospital admission, technicalexpertise, and is not always benign. 18Cysternography does not improve thediagnostic accuracy of clinical and CTcriteria combined, although many doc-tors still use it. 19Continuous intracra-nial pressure monitoring is a usefulprocedure and resultshavebeen uniform.Strong evidence supports that the fre-quent occurrence of B-waves (>50 ofthe recording time) in patients withINPH predicts a good responseto shunt-ing. 7 Unfortunately continuous ICPmonitoring isnot a routine procedure inmost neurosurgical centers.

There are many other diagnosticmodalities, such as the infusion test, theconductance test, cerebrovascular andmetabolic imaging studies. None hasconsistently demonstrated a significantimprovement in predicting shunt-re-sponsiveness. 7

The differential diagnosis of NPHincludes Alzheimer's disease and relateddementias, various causes of Parkin-sonism, most notably Parkinson'sdisease,dementia with Lewy bodies (DLB) andmulti-infarct encephalopathy . Beforeconsidering the diagnosis ofINPH, oneshould exclude other possible explana-tions rather than the other way around.As mentioned before, INPH, is a rela-tivelyraredisease,with an incidence com-parable to Creutzfeld-Jacobdisease,whileAlzheimer's disease, Parkinson's disease,DLBand multi-infarct statearecommonpathologies.

The predictors of a positive shuntresponse are gait predominant disorderthat precedes any cognitive changes, ashort histoty or absence of cognitive im-pairment, a known cause for the devel-opment of the hydrocephalus, absenceof white matter lesion in neuroimagingstudies. When available,the presence ofB-waves for at least 50 of the record-ing time, improvement of symptoms af- 373

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ter CSF drainage and CSF outflow resistanceover 18mmH G/ml per minute are also valuable prognostic factors. In con-trast, severedementia, dementia as the first symptom and se-vereatrophy orwhite matter diseaseon the MRI arepredictorsof a negative response to shunting 7.

One may argue that it isappropriate to shunt a demented,gait-impaired patient, to improve the gait, even though n.osignificant improvement will be expected in cognitive fimc-tion. In that case, the family should have realistic expecta-tions, and be informed of the risks of the shunt. The meanchance ofsignificant improvement aftershunting is30 to 40in INPH and 50-70 in secondary cases.Complications rangebetween 20-40 of the cases, and include strokes, subduralhematomas, shunt malfunctioning, seizuresand problems re-lated to the anesthesia. Serious complications (death, severeresidual deficit) usually arise in patients with severeco-mor-bidities, and are observed in lessthan 8 of the patients withINPH. 7,20Dementia isthe least likelysymptom to improveespeciallyif severe.

In conclusion, INPH is an overestimated, uncommondisorder, with a common clinical triad in the elderly popula-tion. Potential improvement (but probably not reversibiliry)of the gait more than the cognitive dysfunction can be ex-pected only in highly selected patients.

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Neurosurg Psychiatry 2001;70:289-97.14. Savolainen S, Hurskainen H, Paljarvi L, et al. Acta Neurochir2002; 144:515-23.15. Iddon JL, Pickard JD, Cross JL, et al.] Neurol Neurosurg Psy-chiatry 1999;67:723-32.16. VannesteJ, Augustijn P,Tan WF, Dirven c.] NeurolNeurosurg

Psychiatry 1993;56:251-6.17. Maim J, Kristensen B, Karlsson T, et al. Arch Neurol1995;52:783-9.18. Walchenbach R, Geiger E, Thomeer RTWM, Vanneste JAL.

] Neurl Neurosurg Psychiatry 2002;72:503-6.19. Vanneste J, Augustijn P, Gareth AG, et al. Arch Neurol1992;49:366-70.20. Vanneste J, Augustin P, Dirven C, et al. NeuroI1992;42:54-9.

AnelyssaD Abreau, MD, aformer fellow ingeriatric neu-rologyat Brown Medical School/Memorial Hospital ofRl, isageriatric neurologist at the State University of Campinas(UN/CAMP), Brazil. ORRESPONDEN EAnelyssa D'Abreu, MDe-mail: [email protected]

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