Nosology of Juvenile Muscular Atrophy of Distal Upper Extremity: From Monomelic Amyotrophy to Hirayama Disease—Indian Perspective

Abstract

Since its original description by Keizo Hirayama in 1959, “juvenile muscular atrophy of the unilateral upper extremity” has been described under many nomenclatures from the east. Hirayama disease (HD), also interchangeably referred to as monomelic amyotrophy, has been more frequently recognised in the west only in the last two decades. HD presents in adolescence and young adulthood with insidious onset unilateral or bilateral asymmetric atrophy of hand and forearm with sparing of brachioradialis giving the characteristic appearance of oblique amyotrophy. Symmetrically bilateral disease has also been recognized. Believed to be a cervical flexion myelopathy, HD differs from motor neuron diseases because of its nonprogressive course and pathologic findings of chronic microcirculatory changes in the lower cervical cord. Electromyography shows features of acute and/or chronic denervation in C7, C8, and T1 myotomes in clinically affected limb and sometimes also in clinically unaffected contralateral limb. Dynamic forward displacement of dura in flexion causes asymmetric flattening of lower cervical cord. While dynamic contrast magnetic resonance imaging is diagnostic, routine study has high predictive value. There is a need to lump all the nomenclatures under the rubric of HD as prognosis in this condition is benign and prompt diagnosis is important to institute early collar therapy.

Hirayama Disease: A Rare Disease with Unusual Features

“…EMG of the affected muscles shows evidence of chronic denervation, with or without acute denervation changes (fasciculations, positive sharp waves, and fibrillations potentials). However, apparently healthy muscles may also show abnormal EMG findings [4]. …”

Hirayama’s disease: an Italian single center experience and review of the literature

“…Contrariwise, Misra et al and Ammendola et al found no significant differences between standard and flexed position for F-wave parameters, suggesting a different etiology for HD than flexion myelopathy (2,12). Hassan et al and Ghosh et al showed no electromyographic abnormalities of C5 and C6 myotomes (27,28).…”

“…Other typical clinical features include "cold paresis", worsening of symptoms with cold exposure, and no abnormalities of tendons reflexes, sensory disturbance and pyramidal signs (14,15,27).…”

“…During the progressive phase of the disease, neck flexion could lead to a decrease of F-wave persistency; other features are increased latency and high amplitude waveform suggesting denervation/reinnervation. In patients with severe wasting, the F-wave may become unrecordable (27).…”

“…Diagnostic imaging is very important to support clinical suspect of HD. Conventional radiographic examinations of the cervical spine may show loss of cervical lordosis (27) or a hyperflexed cervical motion rate (30). In the 80's, myelography and CT-myelography, in neutral and neck flexed position, were used to evaluate patients with suspected HD demonstrating atrophy of the lower cervical cord and forward displacement of a tightened dural sac (14).…”