AJR:203, September 2014 W315 with clinical information and laboratory data to suggest specific disorders. Yet, almost 60% of inherited WM diseases remain with- out a specific diagnosis [2, 3]. Developing an Approach Helpful Clues in the Clinical Presentation Common neurologic presentations among patients with inherited metabolic diseases include acute encephalopathy, chronic en- cephalopathy, myopathy, movement disor- ders, and behavioral abnormalities. Chronic encephalopathy, with developmental de- lay or psychomotor retardation, is the most common neurologic form encountered in patients with IEM. Seizures, visual failure, extrapyramidal abnormalities, and demen- tia generally occur early in the course of gray matter (GM) diseases. Diseases pre- dominantly affecting cerebral WM tend to present as motor difficulties, with weakness and incoordination. Acute encephalopathy is a presenting feature of several IEM dis- orders, in addition to a variety of acquired medical or surgical conditions. In IEM, de- terioration of consciousness often progress- es rapidly and usually shows no focal neuro- logic deficits. Some of the clinical features that can help in narrowing the differential diagnosis include age of onset of symptoms, normal milestones before presentation, family history, seizure, ocular manifesta- tions, and presence of organomegaly. Most IEM disorders are inherited in an autoso- mal-recessive (AR) pattern. Fewer diseases are inherited in an X-linked pattern. Inborn Errors of Metabolism: Combining Clinical and Radiologic Clues to Solve the Mystery Mohannad Ibrahim 1 Hemant A. Parmar 1 Nickoleta Hoefling 2 Ashok Srinivasan 1 Ibrahim M, Parmar HA, Hoefling N, Srinivasan A 1 Department of Radiology, Division of Neuroradiology, University of Michigan Health System, B2-A209, 1500 E Medical Center Dr, Ann Arbor, MI 48109. Address correspondence to A. Srinivasan ([email protected]). 2 Department of Radiology, State University of New York at Stony Brook, Stony Brook, NY. Neuroradiology/Head and Neck Imaging • Review WEB This is a web exclusive article. This article is available for credit. AJR 2014; 203:W315–W327 0361–803X/14/2033–W315 © American Roentgen Ray Society I nborn errors of metabolism (IEM) comprise a large group of genetic defects with specific bio- chemical and molecular abnor- malities. Most of these disorders are attribut- ed to an enzyme deficiency in the metabolic pathway, including accumulation of substrate (with damage induced by storage or toxicity), or to a deficiency of a product or an essential metabolite. In the brain, these disorders may cause hypomyelination as a result of failure to form specific myelin proteins, delay in my- elination due to an inadequate supply of mye- lin precursors or accumulation of substances toxic to oligodendroglia, demyelination with the loss of normally formed myelin and pres- ervation of the axons, myelin vacuolation (wherein degenerating white matter [WM] is replaced by fluid and vacuolization), and sec- ondary demyelination with the destruction of both axons and myelin [1]. Most leukoen- cephalopathies have a genetic basis, are pro- gressive, and often produce symmetric changes on brain MRI. The imaging evaluation of IEM is met by multiple challenges. Multiple enzyme de- fects can cause the same or similar clinical disorders. Moreover, variable forms of WM diseases can be caused by the same enzyme defect with overlapping symptoms at various ages, which results in a complex radiologic picture of a disease that may have multiple primary and secondary features. A variety of classification systems for leukoencepha- lopathies have been used. Neuroradiologists largely rely on pattern recognition coupled Keywords: imaging white matter disease, inborn errors of metabolism, inherited white matter disease, pediatric white matter disease DOI:10.2214/AJR.13.11154 Received April 29, 2013; accepted after revision January 14, 2014. Presented as an educational exhibit at the RSNA 2011 annual meeting, Chicago, IL. OBJECTIVE. Inborn errors of metabolism in children can be challenging to interpret be- cause of the similarity of their appearances on imaging. There are important clues to the diag- nosis based on clinical history, head circumference (e.g., macrocephaly), geographic distribu- tion of lesions (e.g., subcortical vs deep white matter or frontal vs parietooccipital), and other imaging features (e.g., contrast enhancement, calcification, cysts, and cortical dysplasia). CONCLUSION. In this article, we present an algorithm-based approach to diagnosing pediatric metabolic disease with a discussion of key imaging features. Ibrahim et al. Imaging of Inborn Errors of Metabolism Neuroradiology/Head and Neck Imaging Review Downloaded from www.ajronline.org by 171.243.65.178 on 05/14/23 from IP address 171.243.65.178. Copyright ARRS. For personal use only; all rights reserved
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