eMedicine Specialties > Neurology > Pediatric Neurology

Peroxisomal Disorders: Differential Diagnoses & Workup

Author: Aziza Chedrawi, MD, Consultant, Department of Neurosciences, Section of Pediatric Neurology, King Faisal Specialist Hospital and Research Center
Coauthor(s): Gary D Clark, MD, Associate Professor of Pediatrics, Neurology, Chief of Neurophysiology, Chief of Pediatric Neurology, and Neurosciencediatrics, Baylor College of Medicine, Department of Pediatrics, Texas Children's Hospital
Contributor Information and Disclosures

Updated: Mar 8, 2007

Differential Diagnoses

Ataxia with Identified Genetic and Biochemical Defects
Diseases of Tetrapyrrole Metabolism: Refsum Disease and the Hepatic Porphyrias
Disorders of Carbohydrate Metabolism
Inherited Metabolic Disorders
Neuronal Ceroid Lipofuscinoses

Workup

Laboratory Studies

  • No single test is sufficient to diagnose all peroxisomal disorders. The selection of laboratory studies is based on the clinical presentation.
  • Four diagnostic groups have been described.
    • PBD and POD: These include ZWS, NALD, IRD as part of PBD, and pseudo-NALD and D-bifunctional protein deficiency as part of POD.
    • All 3 types of RCDP
    • All types of X-ALD
    • Refsum, AMACR, hyperoxaluria type I, glutaric aciduria type III, mevalonate kinase deficiency, acatalasemia, and mulibrey nanism
  • In group 1, VLCFA is abnormal in all patients, and normal VLCFA can rule out group 1 disorders.
    • To further differentiate the disorders in this group, additional studies, including tests of erythrocyte plasmalogen, plasma bile-acid intermediates, pristanic acid, and phytanic acid, are recommended.
    • If plasmalogen is deficient, the patient is likely to have PBD.
    • A normal plasmalogen confirms POD. However, plasmalogen may be normal in mild forms of PBD (eg, IRD). In this case, detailed fibroblast studies are needed to differentiate PBD and POD.
  • In group 2, analysis of peroxisomal metabolites in plasma should not be used in the diagnostic work-up for RCDP. Instead, the first study should be an analysis of the plasmalogen level in erythrocytes, which is deficient in all cases of RCDP.
    • After RCDP is confirmed, phytanic acid levels should be checked. If these are abnormally elevated, RCDP I is the likely diagnosis because the level is normal in types II and III.
    • However, because phytanic acid is derived from dietary source, a normal level does not necessarily exclude type I and therefore does not distinguish the 3 types. In this case, enzymatic assay and DNA analysis are recommended to differentiate types II and III.
  • In group 3, elevated plasma VLCFA level is highly reliable in the diagnosis of ALD. Molecular studies are essential in determining a carrier state and especially in prenatal diagnosis, which can be performed in all peroxisomal disorders.
  • Group 4 is clinically heterogeneous. In Refsum disease, an elevated serum level of phytanic acid is reliable in diagnosis. However, enzymatic and molecular analyses are essential for confirmation.
    • In hyperoxaluria type I, liver biopsy is required for enzymatic assay.
    • Urinary excretion of glyoxylic and glycolic acids is increased.
    • In glutaric aciduria type III, molecular studies are not available, and the diagnosis is achieved by means of enzymatic assay.
    • Mevalonate kinase deficiency results in increased urinary excretion of mevalonic acid. However, enzymatic and molecular results may be normal in patients with hyperimmunoglobulin D (IgD).
    • AMACR increases levels of pristanic acid, as detected on urine gas chromatography mass spectrometry, or levels of bile acid intermediates, as per tandem mass spectrometry. Further confirmation is obtained with enzymatic and molecular assays.

Imaging Studies

  • MRI findings in ALD have been well correlated with the characteristic gross neuropathologic features of bilaterally symmetric demyelination in the parieto-occipital region with involvement of the splenium of the corpus callosum (see Image 1). The demyelination then spreads anteriorly and laterally.
    • MRI shows accumulation of contrast material at the advancing margins. This finding is a predictor of disease progression.
    • Other patterns less characteristic than these occur. Examples are early frontal involvement, which is observed in approximately 15% of patients, and an asymmetric mass lesion.
    • Milder ALD phenotypes and AMN commonly affect the brainstem corticospinal tracts and the cerebellar white matter.
    • In the literature, 54% of 112 patients with AMN, brain MRIs were normal, and demonstrable neurologic involvement was confirmed in the spinal cord and peripheral nerves.
  • Magnetic resonance spectroscopy shows a diminution in N -acetyl aspartate due to axonal loss, an increase in choline peaks due to active demyelination, and a mild elevation in lactate peak due to inflammation. Spectroscopic changes precede those demonstrable on MRI.
  • MRI findings in ZWS include neocortical dysplasia (pachypolymicrogyria), germinolytic cysts, and delayed myelination. These finding are attributable to the disordered cytoarchitecture of the cerebral cortex due to neuronal migration defects.
    • Colpocephaly (ie, enlargement of the occipital horns of the lateral ventricles) and hypointensity of white matter have been detected. These findings suggest delayed myelinogenesis.
    • In late stages, cortical atrophy gradually appears.
  • In the remaining peroxisomal disorders, no characteristic findings on neuroimaging have been described.

Other Tests

  • In patients with peroxisomal disorders, such as ZWS, EEG usually shows multifocal spikes in the early stages of disease.
  • In late stages, diffuse irregular high-voltage slow waves, correlated with atrophy, are common features.

Histologic Findings

Neuropathologic lesions in the peroxisomal disorders can be divided into 3 major classes: (1) abnormalities in neuronal migration or differentiation, (2) abnormalities in myelination (defects in the formation or maintenance of myelin in the central white matter and/or in the peripheral nerves), and (3) postdevelopmental neuronal degeneration.

Abnormalities in neuronal migration and differentiation

These abnormalities are most prominent in ZWS and ZWS-like disorders, which are characterized by a unique combination of centrosylvian pachygyria-polymicrogyria. Migration of all neuronal classes, particularly those destined for the outer layers of the cortex, appears to be affected. Less severe cerebral-migration abnormalities, usually in the form of polymicrogyria, are seen in NALD as diffuse, focal, or multifocal lesions that may be associated with subcortical heterotopias; they also are seen in thiolase deficiency and in bifunctional enzyme deficiency.

Cerebral neuronal migration problems have not been identified in IRD, classical adult Refsum disease (ARD), hyperpipecolic acidemia, acyl-CoA oxidase deficiency (pseudo-NALD), ALD, or AMN. In rare reports, RCPD was associated with abnormalities of cerebral neuronal migration. Other subtle neuronal migration problems, apparently asymptomatic, are found in the form of heterotopic Purkinje cells. Defects in neuronal differentiation or terminal migration are common and usually involve the principal nuclei of the inferior medullary olives and, infrequently, the dentate nuclei and claustra. The malformations of these structures consist of dysplasia and simplification. Apparent neuronal loss has also been reported.

Abnormalities in myelination

Lesions of the peripheral nerve can be seen in all peroxisomal disorders with neurologic involvement. Involvement of the peripheral nerves has not been studied sufficiently, except in ARD, which typically results in hypertrophic (ie, onion-bulb) demyelinating neuropathy. Central demyelination and dysmyelination are typically noted in these disorders.

Postdevelopmental neural degeneration

Degenerative changes in the CNS white matter can be classified as 1 of 3 types of lesions: inflammatory demyelination, noninflammatory demyelination, and nonspecific reduction in myelin volume or myelin staining with or without reactive astrocytes.

Inflammatory demyelination, for which ALD is the prototype, is characterized by confluent and bilaterally symmetric loss of myelin in the cerebral and cerebellar white matter. The cerebral lesions usually begin in the parieto-occipital regions and progress asymmetrically toward the frontal or temporal lobes. Arcuate fibers generally are spared, except in chronic cases. The loss of myelin exceeds that of axons, but axonal loss may be considerable. On occasion, lesions involve the brainstem, particularly the pons.

The spinal cord is usually not involved except for bilateral degeneration of the corticospinal tract. Characteristic lamellar and lamellar-lipid inclusions typical of ALD are found in the cytoplasm of Schwann cells or in endoneural macrophages when the peripheral nerves are damaged. Inclusions also may be seen in CNS macrophages but not in oligodendrocytes. Spicular or trilaminar inclusions may be found in the CNS.

The sequence of demyelination in ALD in as follows: enlargement of the extraneural space; vacuolization and myelin swelling with reactive astrocytes and macrophage infiltration; perivascular lymphocytic infiltration and increased permeability of the blood-brain barrier; and loss of myelin with lipophage formation, loss of oligodendroglia and axons, and dystrophic mineralization.

Inflammatory demyelinating lesions may also be seen in AMN, NALD, thiolase deficiency, and some cases of bifunctional enzyme deficiency. Areas of myelin pallor or oligodendroglial loss with or without reactive astrocytes have been seen in ZWS, NALD, IRD, and probably oxidase deficiency.

Noninflammatory dysmyelination is seen mostly in AMN. Myelin pallor is noted with scant interstitial periodic acid-Schiff (PAS)–positive macrophages but no lymphocytes or reactive astrocytes. Dysmyelination has been found in the early stages of the disease; in advanced stages, inflammatory lesions may supervene.

In nonspecific reduction in myelin volume or myelin staining with or without reactive astrocytes, specific neuron or myelinated fiber tracts show major postdevelopmental noninflammatory abnormalities. The first of these is associated with a progressive loss of hearing that has been classified as sensorineural. It can be seen in ZWS, NALD, IRD, ARD, RCDP, and acyl-CoA oxidase deficiency. The second lesion is retinal pigmentary degeneration, which has been reported in ZWS, NALD, IRD, and ARD. In both lesions, the pathologic changes appear to reside in specialized sensory neurons. The third site of pathogenic change is another restricted one in which the neurons of the dorsal nuclei of Clarke and the lateral cuneate nuclei accumulate lamellar lipids containing VLCFA; this has been seen only in ZWS.

Major neuronal and/or axonopathic degeneration is seen in AMN. Patients with AMN have degeneration of the ascending and descending tracts of the spinal cord, especially the fasciculus gracilis and the lateral corticospinal tracts; the pattern is that of wallerian degeneration. The final lesion is cerebellar atrophy, which has been noted in a few patients with RCDP. It is due to loss of Purkinje and granule cells with focal depletion of basket cells. Cerebellar atrophy has been noted in IRD.

More on Peroxisomal Disorders

Overview: Peroxisomal Disorders
Differential Diagnoses & Workup: Peroxisomal Disorders
Treatment & Medication: Peroxisomal Disorders
Follow-up: Peroxisomal Disorders
Multimedia: Peroxisomal Disorders
References
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Further Reading

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Keywords

disorders of peroxisomal biogenesis, PBD, disorders of peroxisomal beta-oxidation, POD, metabolic disorders, metabolic diseases, peroxisome disorders, peroxisome diseases, adrenoleukodystrophy, ALD, neonatal adrenoleukodystrophy, NALD, adrenomyeloneuropathy, infantile Refsum disease, IRD, hyperpipecolic acidemia, rhizomelic chondrodysplasia punctata, RCPD, pseudo–neonatal adrenoleukodystrophy, acyl CoA oxidase deficiency, metabolic kinase deficiency, hyperoxaluria type I, alanine glyoxylate aminotransferase deficiency, bifunctional enzyme deficiency, pseudo-Zellweger syndrome, peroxisome thiolase deficiency, acatalasemia, catalase deficiency, dihydroxy acetone phosphate acyltransferase deficiency, DHAP-AT, alkyl-DHAP synthase deficiency, glutaric aciduria, adult Refsum disease, ARD, classic Refsum disease, phytanoyl CoA hydroxylase deficiency, Zellweger syndrome, ZWS, microbody, microbodies, hyperpipecolic academia, HPA, cerebrohepatorenal syndrome, peroxisomal 2-methylacyl-CoA racemasedeficiency,AMACR, Lorenzo's oil

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Contributor Information and Disclosures

Author

Aziza Chedrawi, MD, Consultant, Department of Neurosciences, Section of Pediatric Neurology, King Faisal Specialist Hospital and Research Center
Aziza Chedrawi, MD is a member of the following medical societies: American Academy of Neurology
Disclosure: Nothing to disclose.

Coauthor(s)

Gary D Clark, MD, Associate Professor of Pediatrics, Neurology, Chief of Neurophysiology, Chief of Pediatric Neurology, and Neurosciencediatrics, Baylor College of Medicine, Department of Pediatrics, Texas Children's Hospital
Gary D Clark, MD is a member of the following medical societies: American Academy of Neurology, American Academy of Pediatrics, American Epilepsy Society, Child Neurology Society, and Society for Pediatric Research
Disclosure: Nothing to disclose.

Medical Editor

David A Griesemer, MD, Professor, Departments of Neurology and Pediatrics, Medical University of South Carolina
David A Griesemer, MD is a member of the following medical societies: American Academy of Neurology, American Epilepsy Society, and Child Neurology Society
Disclosure: Nothing to disclose.

Pharmacy Editor

Francisco Talavera, PharmD, PhD, Senior Pharmacy Editor, eMedicine
Disclosure: Nothing to disclose.

Managing Editor

Kenneth J Mack, MD, PhD, Senior Associate Consultant, Department of Child and Adolescent Neurology, Mayo Clinic
Kenneth J Mack, MD, PhD is a member of the following medical societies: American Academy of Neurology, Child Neurology Society, Phi Beta Kappa, and Society for Neuroscience
Disclosure: Nothing to disclose.

CME Editor

Selim R Benbadis, MD, Professor, Director of Comprehensive Epilepsy Program, Departments of Neurology and Neurosurgery, University of South Florida School of Medicine, Tampa General Hospital
Selim R Benbadis, MD is a member of the following medical societies: American Academy of Neurology, American Academy of Sleep Medicine, American Clinical Neurophysiology Society, American Epilepsy Society, and American Medical Association
Disclosure: Nothing to disclose.

Chief Editor

Nicholas Y Lorenzo, MD, Chief Editor, eMedicine Neurology; Consulting Staff, Neurology Specialists and Consultants
Nicholas Y Lorenzo, MD is a member of the following medical societies: Alpha Omega Alpha and American Academy of Neurology
Disclosure: Nothing to disclose.

 
 
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