Monomelic Amyotrophy (Hirayama Disease) With Upper Motor Neuron Signs: A Case Report

Abstract

Monomelic amyotrophy (MMA), also known as Hirayama disease, is a sporadic juvenile muscular atrophy in the distal upper extremities. This disorder rarely involves proximal upper extremities and presents minimal sensory symptoms with no upper motor neuron (UMN) signs. It is caused by anterior displacement of the posterior dural sac and compression of the cervical cord during neck flexion. An 18-year-old boy visited our clinic with a 5-year history of left upper extremity pain and slowly progressive weakness affecting the left shoulder. Atrophy was present in the left supraspinatus and infraspinatus. On neurological examination, positive UMN signs were evident in both upper and lower extremities. Electrodiagnostic study showed root lesion involving the fifth to seventh cervical segment of the cord with chronic and ongoing denervation in the fifth and sixth cervical segment innervated muscles. Cervical magnetic resonance imaging (MRI) showed asymmetric cord atrophy apparent in the left side and intramedullary high signal intensity along the fourth to sixth cervical vertebral levels. With neck flexion, cervical MRI revealed anterior displacement of posterior dural sac, which results in the cord compression of those segments. The mechanisms of myelopathy in our patient seem to be same as that of MMA. We report a MMA patient involving proximal limb with UMN signs in biomechanical concerns and discuss clinical importance of cervical MRI with neck flexion. The case highlights that clinical variation might cause misdiagnosis.

Hirayama Disease: A Rare Disease with Unusual Features

“…However, early diagnosis is necessary because a cervical collar may arrest the progression of the disorder by limiting the neck flexion. Physiotherapy is also helpful in preventing complications resulting from immobility such as joint stiffness and muscle wasting [1]. …”

“…The typical clinical features include insidious onset and slow progression of unilateral or bilateral muscular atrophy with weakness of the forearms and hands. Sensory disturbance, autonomic involvement, and upper motor neuron (UMN) signs like hyperreflexia and hypertonia are rare [1]. The motor neuron disease (MND) is a very close differential diagnosis of HD, but, unlike MND, the disease progresses initially and is followed by spontaneous arrest several years after the onset.…”

Hirayama Disease- A Classic Case with Typical MRI Findings

“…So, on flexion normal compensation cannot happen leading to compression of the cord against vertebral bodies due to anterior shifting of the posterior dural wall which in turn causes disturbances in microcirculation in the anterior spinal artery territory in the lower cervical spinal cord. [1], [2], [13] Multiple episodes of ischemia and chronic trauma to the spinal cord due to repeated flexion leading to myelopathy which appears as asymmetric lower cervical cord thinning in the MRI. Flexion MRI shows forward migration dura matter wall with enlarged posterior epidural space.…”

“…There is anterior displacement of dural sac during cervical flexion which impairs the anterior horn cells of the distal cervical spinal cord secondarily. [1,2] it mostly affects males in 2 nd -3 rd decades. Clinically, the patient mainly presents with unilateral or bilateral muscular atrophy and weakness of the forearms and hands which is insidious in onset and is slowly progressive.…”

ALS-Mimics

“…Während initial meist nur eine Extremität betroffen ist, kommt es im Verlauf der Erkrankung häufig zu einer Progression auf die Gegenseite, wobei die Symptomatik meist asymmetrisch bleibt [51]. Auch die unteren Extremitäten können betroffen sein, i. d. R. jedoch in geringerem Ausmaß [56]. Teilweise scheinen die Paresen eine Zunahme bei Kälteexposition zu zeigen, evtl.…”