The value of the MRI in the diagnosis of PMD in a 14-year-old Japanese boy is reported from the Depts of Pediatrics and Radiology, Tokyo Children’s Rehabilitation Hospital, Tokyo 190-12, Japan. The child presented with rotatory nystagmus at 2 weeks after birth, titubation at 6 months, spasticity at 1 year, and a masklike facial expression at 3 years of age. He was markedly retarded at 14 years and examination revealed spasticity, intention tremor, joint contractures, nystagmus and normal fundi. Head circumference, nerve conduction studies, and lysosomal enzymes were normal. CT showed ventricular enlargement, cerebellar atrophy, but normal appearing white matter. MRI demonstrated diffuse changes in white matter with sparing of scattered small areas consistent with a “tigroid pattern“ of myelin preservation characteristic of PMD. 
COMMENT. Described by Pelizaeus in 1885 and by Merzbacher in 1910, this heredofamilial disease transmitted as an X-linked recessive character and occurring chiefly in males is a slowly progressive leukodystrophy with a long course, patients not infrequently surviving into middle age. When the family history is negative, as in the above case, confirmation of the diagnosis during life is difficult but may be facilitated by the MRI findings and may permit appropriate genetic counseling.