Juvenile Muscular Atrophy of the Proximal Upper Extremity as So-Called Proximal-Type Hirayama Disease: Case Report and Review of the Literature

Hirayama disease is a distinct type of cervical myelopathy characterized by juvenile onset of unilateral muscular atrophy of a distal upper extremity. We report herein a case with Hirayama disease-like juvenile muscular atrophy involving proximal muscles in the upper extremities. In this case, in the flexion position of the neck, cervical magnetic resonance imaging revealed that the spinal cord was compressed by expansion of the posterior extradural space with forward displacement of the dura matter. These neuroimaging results are identical to those of Hirayama disease. However, the involved muscles in this case were the proximal muscles, unlike Hirayama disease. Five previous cases have displayed this rare subtype of Hirayama disease. The cause of the unique phenotype may be abnormal cervical column alignment, with upper cervical kyphosis producing a higher apex of the vertebral level in a cervical flexion position, resulting in mid-cervical segmental myelopathy.

Bimelic Hirayama Disease: Clinical Dilemma Solved by Imaging

Hirayama disease (juvenile muscular atrophy of distal upper extremity) is a cervical myelopathy predominantly affecting adolescent males. It is characterized by progressive muscular weakness and atrophy of unilateral or asymmetrically bilateral distal upper limbs. We report a case of an 18-year-male painter, who presented with gradually progressive, symmetrical bilateral weakness of hands and forearm for the last two years. On the basis of clinical examination, a provisional diagnosis of lower motor neuron type of symmetrical distal weakness due to heavy metal intoxication was kept. However, imaging studies helped in making a definitive diagnosis of Hirayama disease. The patient was advised cervical collar, and there was no progression in symptoms after six months of followup. Due to the rarity of bilateral symmetrical involvement in Hirayama disease, it remains obscured or unsuspected clinically, and MRI plays a pivotal role in diagnosis.

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

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.