[Deep peroneal nerve palsy associated with hypothyroidism].

Carpal tunnel syndrome is well known to be associated with hypothyroidism, but other mononeuropathies have been rarely reported. We report a 65-year-old male who showed right deep peroneal nerve palsy caused by hypothyroidism. The patient was admitted to our hospital because of general fatigue and right drop foot. On admission, bilateral pretibial pitting edema was observed, predominant on the right side. There was no muscle contraction in the right anterior tibial muscle and extensor hallucis longus in addition to slight weakness of the proximal muscles; whereas, muscle atrophy of the anterior tibial muscle was not noted. There was no sensory disturbance. On an electrophysiological examination, there was no muscle action potentials by the stimulation of the right deep peroneal nerve. Other nerves showed normal results both in the conduction velocity and in the compound action potential. Two months after the administration of levothyroxine sodium (0.025 mg/day), the right deep peroneal nerve palsy was completely recovered, associated with disappearance of pretibial edema. It is not yet determined which of axonopathy or demyelination is dominantly responsible for neuropathy associated with hypothyroidism. These results suggested a conduction block in deep peroneal nerve associated with focal edema. It is necessary to consider hypothyroidism as well as trauma, diabetes mellitus, and vasculitis when investigating mononeuropathy of deep peroneal nerve.