IgG4-Related Peripheral Neuropathy with Unilateral Cervical Nerve Root and Brachial Plexus Swelling: A Case Report

A 64-year-old man presented with left upper limb weakness and dysesthesia for 4 months. Magnetic resonance imaging demonstrated swelling from the 6th–8th left cervical nerve roots to the left brachial plexus. The serum IgG4 level was elevated (762.7 mg/dL). ¹⁸F-FDG-PET showed high uptake in the mediastinal lymph nodes, and biopsy revealed infiltration of IgG4-positive plasma cells. We diagnosed IgG4-related neuropathy, and steroid therapy administration improved the symptoms. IgG4-related disease should be considered in the differential diagnosis of peripheral nerve swellings. If biopsy of the disordered nerves is difficult, lymph nodes or other organs should be considered.