Abstract
The present case is probably a rare and variant type of spinal muscular atrophy, similar to Charcot-Marie-Tooth type of progressive muscular atrophy (Dyck PJ and Lampert EH: Arch Neurol 18: 603, 1968) with difference in age of onset and in clinical findings of selective muscular weakness in anterior tibial muscle without signs of muscular involvement of the upper extremities.
This 6-year-2-month old boy was a product of nonrelated parents without neuromuscular disorders in the family history. He was noticed to have disability of dorsal flexion in the foot joints at 6 months of age, and steppage gait on walking later. Motor development was normal. Running was possible at 2 years of age, except flaccid drop feet persisting without improvement. He was a slender but alert boy.
Neurological examination revealed normal cranial nerves without cerebellar signs or sensory disturbance. No evidence of ataxia, fasciculation and contracture of joints was observed. Deep tendon reflexes in the lower extremities were all hypoactive without pathological reflexes. Flaccid drop feet with pes cavus and hammer toes were persisting.
Muscle testing (Daniels L) revealed trace in anterior tibial muscle, good in peroneal muscle, and or normal in other muscles of all the upper and lower extremities. Blood chemistry was normal.
Motor nerve conductinn velocity, terminal latency and M wave amplitude in the right median, tibial and peroneal nerves were all normal. Sensory nerve conduction velocity, action potential in the right median and sural nerves were also normal. Strength-duration curve and chronaxy were normal in peroneal muscle, but showed a partial denervation pattern in anterior tibial muscle.
Light and electron microscopic findings of biopsied sural nerve were normal. However, histochemical studies of biopsied quadriceps femoris disclosed predominance of type I fiber with small group atrophy, and reduced number of type 2 fiber with hypertrophy. An increase in both glycogen particles and myofibrils with dense cytoplasmic bodies surrounded by lighter halos and myeloid bodies in atrophied muscle fibers was observed electron-microscopically.
