Pelizaeus-Merzbacher disease. Contribution of magnetic resonance imaging to an early diagnosis.

The lesions of the cerebral white matter which characterize Pelizaeus-Merzbacher disease are classically observed at pathological examination. An early diagnosis can now be obtained by magnetic resonance imaging (MRI). In an eutrophic first son born at term, stridor, nystagmus-like eye movements and axial hypotonia were noted immediately after birth and pyramidal signs appeared at 2 months, the only extra-clinical finding at that age being prolonged latencies of evoked visual potentials. An MRI exploration, performed at 3 months, showed that compared with the grey matter the white matter emitted a low-intensity signal on the T1-weighted sequence and a high-intensity signal on the T2-weighted sequence (signal inversion), such diffuse and symmetrical MRI abnormalities being typical of dysmyelination. When combined with suggestive clinical signs, these abnormalities confirm the diagnosis of Pelizaeus-Merzbacher disease, even in the absence of a familial history, and make it possible to warn the parents of the poor prognosis and the risk of recurrence among future sons.