Proximal and proximo-distal bimelic amyotrophy: Evidence of cervical flexion induced myelopathy.

This report aims at describing two new clinical phenotypes associated with classical features of cervical flexion induced myelopathy (CFIM). The description is of a prospective case series of six young males presenting with progressive bilateral proximal/proximo-distal amyotrophy of upper limbs and demonstrating the typical MRI characteristics of Hirayama disease. All underwent detailed clinical, electrophysiologcal and imaging studies. The affected muscles were shoulder girdles and arms in proximal form (n = 2) and the entire upper limbs in proximo-distal form (n = 4). The mean age at onset was 21.0 ± 3.3 years, duration of illness was 6.7 ± 3.4 years, period of progression was 39.0 ± 27.3 months followed by a stable phase of 45.0 ± 50.0 months. All had severe wasting and weakness of affected muscles leading to significant disability. Nerve conduction studies revealed grossly reduced compound muscle action potential amplitudes with neurogenic pattern on electromyography of affected muscles. On MRI all revealed evidence of cervical cord atrophy with signal changes, dural detachment and extensive posterior epidural enhancement (variably from C1 to T2 level). Altered cervical curvature was prominent. In conclusion, hitherto unreported, we describe two additional clinical phenotypes (proximal and proximo-distal forms) of Hirayama disease demonstrating the cardinal imaging features of CFIM.