Nonsystemic vasculitic neuropathy in a patient with IgG-monoclonal gammopathy of undetermined significance: A case report.

Monoclonal gammopathy of undetermined significance (MGUS) is a plasma cell proliferative disorder that consistently precedes multiple myeloma. Peripheral neuropathy in patients with IgG-MGUS tends to vary in clinical phenotype. We report a rare case of a patient with IgG-MGUS who had nonsystemic vasculitic neuropathy (NSVN). A 56-year-old Japanese woman presented with progressive sensory ataxia with episodic paresthesia. Her clinical and laboratory values were compatible with IgG-MGUS. A nerve conduction study suggested possible chronic inflammatory demyelinating polyneuropathy. However, intravenous immunoglobulin therapy was not effective. A sural nerve biopsy specimen revealed mildly reduced myelinated fiber density and myelin ovoid formation, with epineural arterioles infiltrated by inflammatory cells. We accordingly diagnosed her condition as NSVN. She was accordingly started on oral prednisolone (40 mg/d) at 3 months after the onset of her neurological symptoms. At 1 year after the oral prednisolone treatment was begun, the patient's neurological symptoms showed no worsening. These findings indicate NSVN as a possible cause of peripheral neuropathy in patients with IgG-MGUS. Cumulatively, our findings highlight the need for a nerve biopsy for peripheral neuropathy in patients with IgG-MGUS as a possible cause of NSVN. The early diagnosis of NSVN is expected to be beneficial for such patients.