Anti-MAG Polyneuropathy

Case Study A
A 62-year-old man had an eighteen-month history of having trouble walking. He complained of a slowly and steadily progressive feeling of stiffness and tiredness of his legs. He also experienced pins and needles sensations in his legs. He complained of unsteady gait, especially in the dark and on uneven ground, and difficulty with use of his hands for fine tasks, such as buttoning and writing, because of reduced feeling in the fingertips. He denied pain and stated that his bowel, bladder, and sexual functions were unaffected. Although his gait was unsteady, he felt that his strength was normal. A course of treatment elsewhere with chlorambucil for seven months, prompted by the discovery of a small amount of M-protein in the serum, had not helped. He was otherwise healthy and had no significant medical problems. Thorough evaluation by an experienced neurologist had disclosed no cause for his neuropathy.

He appeared healthy. His gait was ataxic and he could not perform tandem walking. The Romberg sign was present. Strength was normal in the arms and hands, but decreased minimally in the distal legs (4.5/5 foot dorsiflexors). Deep tendon reflexes (DTRs) were decreased at the wrists and knees and absent at the ankles. Vibration sense was absent in the feet and position sense was decreased. Pin and light touch were both minimally diminished distally in a stocking distribution. The nerves were slightly thickened.

The patient had a mostly sensory polyneuropathy, primarily affecting large sensory fibers, and most likely an axonopathy. Differential possibilities included toxins (pyridoxine), the sensory neuropathy syndrome associated with occult neoplasia or autoimmune disease (Sjogren's, idiopathic) and anti-MAG associated polyneuropathy, as well as the rare sensory variant of chronic inflammatory demyelinating polyneuropathy (CIDP).

EMG demonstrated a demyelinating polyneuropathy. Immunofluorescent staining of nerve biopsy showed IgM deposition on the myelin sheaths. Serological studies revealed elevated anti-MAG antibody titers. Therefore, a diagnosis of polyneuropathy associated with anti-MAG antibody activity was made.

Treatment options included plasmapheresis, cyclophosphamide, and prednisone which resulted in complete remission with only minor signs remaining and no symptoms.