Hirayama disease usually selectively involves lower cervical myotomes (C8, T1). Thus, patients usually manifest with atrophy and weakness of small hand muscle. Predominant isolated involvement of proximal arm is rarely reported in Hirayama disease. Here, we report a case of Hirayama disease who had focal weakness and wasting, mainly confined to right biceps brachii muscle, with prominent shifting of dural sac in C4-5 segment by dynamic flexion magnetic resonance imaging (dfMRI), which may explain this unusual distribution of the disease.
Amyotrophy, monomelic