Symposium 3: Motor neuron disease SY3.1. Monomelic amyotrophy – Experience from a large cohort

Abstract

In 1959, Hirayama described the clinical entity of progressive atrophy of distal muscles of a single upper limb and called it Hirayama disease (HD). Later on Gourie-Devi from India coined the term Monomelic Amyotrophy. The other phenotypes described by us are: Distal Bimelic, Proximo-distal bimelic and unilateral/bilateral proximal amyotrophy. Illness has sporadic occurrence with male preponderance, but familial forms are also reported. Most cases are described from Asian countries. There is insidious onset and slowly progressive weakness and atrophy of intrinsic hand and forearm muscles, with oblique atrophy with sparing of Brachioradialis and reverse split hand syndrome. Typically, they have cold paresis. In the year 2000, HD was confirmed to occur secondary to dynamic compression of the lower Cervical Cord due to forward displacement of the tight cervical dural sac causing arterial/venous ischemic damage to anterior horn cells. Classically MRI at cervical level shows “eye of the snake” appearance, reverse lordosis, dural detachment with forward displacement and epidural venous congestion and enhancement. From our experience on 480 cases seen over 38 years, the mean age at onset is 19.5 years; range,15–25 years, with majority being in the progressive phase. Progression generally occurs over 5 years but even rapidly and slower in certain cases, and the disability is moderate to severe in the majority. Rarely patients experienced Lhermitte’s phenomenon and had spasticity of the lower limbs with sphincter disturbance. Over the last 4.5 years, 101 cases with HD have undergone anterior cervical decompressive surgery at our center. Predominantly C5-C6 single level discectomy and fusion was performed. Pre-operative and serial post-operative assessment included, Fugl Meyer and Jebsen Taylor hand function tests which demonstrated significant improvement in functions in the majority at 3,6,12 and 24 months follow-up. In the remaining patients the illness has stabilized. No major complications were encountered except for post-operative neck pain and restricted movements which improved in a few weeks. To conclude Hirayama disease is now confirmed to be a cervical compressive myelopathy due to dynamic neck flexion induced ischemic damage and surgery has a major role in stabilizing / improving the neurological deficits. The most appropriate term for this disease would be “CERVICAL FLEXION INDUCED MYELOPATHY”.