Background: Hirayama disease (brachial monomelic amyotrophy) is a unilateral or grossly asymmetric bilateral disease. Bilaterally symmetric involvement has never been described.
Methods: Based on cardinal clinical and MRI criteria, a total of 106 patients with Hirayama disease from two tertiary care hospitals of North India seen between 1992 and 2008 formed the basis of this study. All those found to have bilaterally symmetric involvement on clinical and electrophysiologic basis were evaluated for clinical, electrophysiologic, and MRI correlates other than those required for the diagnosis.
Results: Eleven patients, who constituted around 10% of all the patients with Hirayama disease, were found to have bilaterally symmetric involvement. Nine of them had a history of unilateral onset. The important characteristics of this type of presentation included severe weakness and wasting in C7, C8, and T1 myotomes that frequently spilled over to C6 segment, predominant autonomic dysfunction in distal upper extremities in the form of cold paresis, cold skin, excessive sweating, and hair loss over the dorsum of the hands, and a very prominent bilateral minipolymyoclonus. MRI during complete flexion of neck showed severe flattening of lower cervical spinal cord against C5-C6 vertebral bodies and development of a crescent-shaped enhancing epidural space extending from C4 to T2 spine.
Conclusion: Bilaterally symmetric Hirayama disease is a severe form of a classic disease which remains undiagnosed due to a common notion that it is a unilateral or grossly asymmetric disease. This description calls for review of the term "brachial monomelic amyotrophy" described to denote this disease.