• footdrop
• peroneal lesion

A 45 year old man presented with a history of footdrop. Years before examination he had noticed difficulties with pronation and mild difficulties with elevation of the right toe. He then presented with a 14 day history of acute complete loss of power of foot elevation and pronation and severe paresis of toe extension. Supination and plantar flexion of the foot and toes were intact. Nerve conduction studies showed an axonal lesion of the peroneal nerve. Needle EMG showed acute denervation and reduced interference pattern of the anterior tibial muscle. The long peroneal muscle showed an increase of tissue resistance to needle insertion compatible with muscle fibrolipomatosis. Moreover, there was absence of voluntary muscle activity and infrequent pathological spontaneous activity in this muscle. Magnetic resonance imaging of the lower leg disclosed a fatty degeneration of the long peroneal muscle (fig 1 A, arrows) on T1 weighted images with only a few residual muscle fibres but with a regular circumference of the muscle. The remaining muscles of the lower leg appeared morphologically intact. On fat suppressed T2 weighted images (fig 1 B) the anterior tibial muscle and the extensor digitorum muscle (arrows) showed an increased signal consistent with acute denervation.¹ Thus, the diagnosis of a chronic lesion of the superficial ramus of the peroneal nerve associated with an acute denervation of the deep ramus was confirmed by MRI.