A woman with forearm amyotrophy

Area of Science:

• Neurology
• Clinical Case Study

Background:

• Hirayama disease is a rare, sporadic monomelic amyotrophy affecting the distal arm.
• It is characterized by forearm muscle wasting, cold-induced weakness (paresis), and burning pain (causalgia).

Purpose of the Study:

• To present a case of Hirayama disease in a 33-year-old woman.
• To discuss the diagnostic findings and potential pathomechanisms.
• To highlight the favorable outcome with partial motor recovery.

Main Methods:

• Clinical examination including assessment of muscle strength and sensation.
• Electromyography (EMG) and nerve conduction studies (NCS).
• Magnetic resonance imaging (MRI) of the cervical spine in neutral and flexion positions.
• Serum antibody testing (IgG anti-GM1).

Main Results:

• Forearm amyotrophy sparing the brachioradialis muscle was observed.
• EMG showed denervation in the extensor digitorum communis; NCS ruled out multifocal motor neuropathy.
• Cervical spine MRI was normal in all positions.
• Serum IgG anti-GM1 antibodies were transiently elevated.
• Partial motor recovery occurred within 15 months.

Conclusions:

• Hirayama disease can present in women with distinct clinical features.
• Diagnostic workup involves EMG, NCS, and cervical MRI.
• The pathogenesis remains debated, possibly involving chronic anterior horn ischemia or being a variant of lower motor neuron disease.
• The condition typically shows a favorable prognosis with partial recovery.