Teaching Case

Psychomotor retardartion, ataxia, nystagmus.

The patient presented with moderate psychomotor retardartion, ataxia, and abnormal eye and head movements at age three. On MR imaging at 0.5 Tesla, conventional T1 and T2-weighted images were obtained. In one of the follow-up neurologic examinations elsewhere, at age 8, proton MR spectrocopy was requested from our department. Proton MR spectrocopy was obtained at 1.5 Tesla (TR=1500 msec, TE=40 msec).

Pelizaeus-Merzbacher disease is a rare disease covering five different clinical types of sudanophilic leukodystrophies, caused by a severe deficiency of myelin-specific lipids (lipophilin), which is necessary for development of oligodendrocytes. The main types of Pelizaeus-Merzbacher disease consist of an X-linked recessive form (type I, the classical form), and type II, the connatal, either X-linked recessive or autosomal recessive forms (the early infantile form). Transitional forms are also described. The patients clinically present with nystagmus, ataxia, and psychomotor retardartion. The current patient (a three-year-old girl) represents a transitional form of Pelizaeus-Merzbacher disease. On MRI, a tiger-skin appearance in the cerebral white matter is quite characteristic, which is believed to represent preserved myelin around perivascular spaces. Otherwise, there is widespread lack of myelination sparing the subcortical U-fibers. Proton MR spectroscopy studies in Pelizaeus-Merzbacher disease almost always reveal normal peaks, and normal values of N-acetylaspartate/creatine, and choline/creatine ratios, reflecting well preserved neurons and axons, and lack of active demyelination in the disease. Normal spectroscopy findings can aid distinguishing Pelizaeus-Merzbacher disease from other leukodystrophies, neurodegenerative, and metabolic disorders, as in most of these spectroscopy findings are usually abnormal.