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

RATIONALE: 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). PATIENT CONCERNS: 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. DIAGNOSES: We accordingly diagnosed her condition as NSVN. INTERVENTIONS: She was accordingly started on oral prednisolone (40 mg/d) at 3 months after the onset of her neurological symptoms. OUTCOMES: At 1 year after the oral prednisolone treatment was begun, the patient's neurological symptoms showed no worsening. LESSONS: 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.