Progressive neural muscular atrophy in a case of phenylketonuria.

Clinical, neurophysiological and nerve-biopsy findings are described in a 13-1/2-year-old boy with classical phenylketonuria who developed progressive muscular atrophy. Clinical examination revealed atrophy of the calf muscles and pes varus. Tendon jerks were brisk in the upper extremities but were absent in the right leg and weak in the left leg. Nerve conduction velocities of the median and peroneal nerve were strongly reduced. Light- and electronmicroscopic investigation of sural nerve biopsy revealed axonal dystrophy and 'onion-bulb' formation of the Schwann cells. It is assumed that the combination of phenylketonuria and progressive muscular atrophy in this patient is an accidental occurrence.