A 64-year-old, right-handed woman was admitted to the hospital because of motor and sensory impairment in her right arm.Two years before admission, generalized lymphadenopathy had been diagnosed. At that time, the levels of urea nitrogen, creatinine, and calcium were normal. The hematocrit was 34.8 percent. Microscopical examination of a bone marrow specimen showed increased iron storage. Immunologic tests were performed (Table 1). Immunoelectrophoresis showed an IgG kappa monoclonal protein (1300 mg per deciliter). No Bence Jones protein was detected. A gallium scan showed no abnormalities. The angiotensin-converting enzyme level was normal. Repeated computed tomographic (CT) scans of the thorax showed a small, stable pulmonary nodule in the right upper lobe, with bilateral axillary, mediastinal, and left hilar lymphadenopathy. Biopsy specimens of axillary lymph nodes revealed proteinaceous lymphadenopathy. Immunophenotyping of a peripheral-blood specimen showed no evidence of a lymphoproliferative disorder.Eighteen months before admission, progressive weakness developed in the extensors of the fingers of the right hand. Thirteen months before admission, the sensation of a pinprick was slightly reduced in the fourth finger of the right hand and the second finger of the left hand and in the distribution of the right saphenous nerve. An electromyographic study was performed (Table 2).Ten months before admission, progression of the weakness in the right hand was noted, and the sensation of a pinprick was decreased over the palmar aspect of the right hand. Immunologic tests were performed (Table 1).Intravenous injections of immune globulin over a period of five days were ineffective. The impairment in the right arm worsened, and pain developed in the right wrist and metacarpophalangeal joints and in the left hand. Treatment with amitriptyline, nortriptyline, carisoprodol, and tramadol had intolerable side effects, and a six-day course of methylprednisolone, propoxyphene, and gabapentin did not relieve the pain.Five months before admission, an electromyographic study was performed ( Table 2). The erythrocyte sedimentation rate was 59 mm per hour. The levels of vitamin B 12 and thyrotropin were normal. Immunologic tests were performed (Table 1). Microscopical examination of a specimen from a right-sided sural-nerve biopsy showed no evidence of vasculitis.Two months before admission, the fingers of the left hand became increasingly sensitive, with progressive sensory loss. The patient had sustained a small, second-degree burn on a finger, without pain. Hoarseness developed, and examination showed paralysis of the left vocal cord. A CT study of the neck and chest was unchanged. The patient was referred to this hospital. *There was an IgG kappa M component at a moderate concentration. †GALOP denotes gait-disorder autoantibody, late-onset polyneuropathy.