Examination and initial investigations

The cranial nerves were normal. There was predominantly distal weakness, more marked in the legs, MRC grade 3/5. He had absent tendon reflexes, down going plantar responses, and “glove and stocking” sensory loss to pain, light touch, vibration, and joint position sense. General examination was normal.

Nerve conduction studies showed reduced sensory action potentials, absent f-waves, and slow motor conduction velocity in keeping with a predominantly demyelinating mixed motor and sensory neuropathy with minimal axonal involvement (table 1). There was partial motor conduction block. The cerebrospinal fluid was acellular with a slightly raised protein of 0.63 g/l (reference range 0.1–0.4) and normal glucose concentration. Full blood count, urea, electrolytes, liver function tests, blood glucose, calcium, vitamin ^B12 level, auto-antibody tests for vasculitis, serum immunoglobulin concentrations, and urine porphyrins were all normal or negative. However, an IgG lambda paraprotein was detected on immunofixation at a titre of 2 g/l. The urine was negative for Bence Jones protein. He had no excess of plasma cells on bone marrow aspirate and a normal trephine. An initial radiographic skeletal survey was normal. Endocrine function tests showed a low testosterone of 5.7 nmol/l (range 9–36), …