A case of brachial multisegmental amyotrophy caused by spontaneous spinal cerebrospinal fluid leak leading to epidural fluid collection

•A 68-year-old man presented with slowly progressive upper-extremity weakness.•Spinal MRI revealed abnormal signals in the anterior horns at C3–C5 spinal levels.•Spinal MRI detected epidural fluid collection at C6–T6 spinal levels.•Surgical dural repair inhibited disease progression.•Brachial multisegmental amyotrophy is a potentially treatable disease. A 68-year-old man suffered from slowly progressive proximal upper extremity weakness for 17 years. Examination revealed bilateral C5–C6 muscle weakness. Upon spinal magnetic resonance imaging (MRI), the T2-weighted images showed high-intensity signals in the anterior horns at the C3–C5 spinal levels, with ventral epidural fluid collection at the C6–T6 spinal levels. Brain MRI also revealed hemosiderin deposition in the cerebellum. The patient was ultimately diagnosed with brachial multisegmental amyotrophy caused by spontaneous spinal cerebrospinal fluid leak with superficial siderosis. During surgery, a dural defect was identified at the T2–T3 spinal level, which was subsequently repaired. At the 60-month follow-up, no signs of disease progression were noted. This disease could potentially be treated through surgery and should be included in the differential diagnosis of slowly progressive segmental amyotrophy.