甲状腺機能低下症に伴う深腓骨神経麻痺

Deep Peroneal Nerve Palsy Associated with Hypothyroidism

　甲状腺機能低下症に伴って出現した右深腓骨神経麻痺の1例を経験した。本症例では両下肢のpitting edemaがみられ，神経学的には四肢の近位筋の軽度の筋力低下に加え右深腓骨神経の支配筋群に限局した高度の麻痺を認めた。治療により甲状腺機能の正常化に伴い同神経の麻痺も著明な改善を示し約2カ月でほぼ完全に回復した。本例では下腿浮腫に伴う伝導ブロックをその機序として考えた。原因不明の深腓骨神経麻痺の場合には甲状腺機能の検索が必要であると考えられた。

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 admis-sion, 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 weak-ness of the proximal muscles ; whereas, muscle atrophy of the anterior tibial muscle was not noted. There was no sensory disturbance. On an electro-physiological 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 administra-tion 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 neu-ropathy associated with hypothyroidism. These results suggested a conduction block in deep pero-neal nerve associated with focal edema. It is nece-ssary to consider hypothyroidism as well as tra-uma, diabetes mellitus, and vasculitis when inves-tigating mononeuropathy of deep peroneal nerve.