Clinical heterogeneity in mild chronic inflammatory demyelinating polyneuropathy

Rapid and reversible responses to IVIG in autoimmune neuromuscular diseases suggest mechanisms of action involving competition with functionally important autoantibodies

Intravenous immunoglobulin (IVIG) is widely used in autoimmune neuromuscular diseases whose pathogenesis is undefined. Many different effects of IVIG have been demonstrated in vitro, but few studies actually identify the mechanism(s) most important in vivo. Doses and treatment intervals are generally chosen empirically. Recent studies in Guillain-Barré syndrome and chronic inflammatory demyelinating polyneuropathy show that some effects of IVIG are readily reversible and highly dependent on the serum IgG level. This suggests that in some autoantibody-mediated neuromuscular diseases, IVIG directly competes with autoantibodies that reversibly interfere with nerve conduction. Mechanisms of action of IVIG which most likely involve direct competition with autoantibodies include: neutralization of autoantibodies by anti-idiotypes, inhibition of complement deposition, and increasing catabolism of pathologic antibodies by saturating FcRn. Indirect immunomodulatory effects are not as likely to involve competition and may not have the same reversibility and dose-dependency. Pharmacodynamic analyses should be informative regarding most relevant mechanism(s) of action of IVIG as well as the role of autoantibodies in the immunopathogenesis of each disease. Better understanding of the role of autoantibodies and of the target(s) of IVIG could lead to more efficient use of this therapy and better patient outcomes.

Steroid-induced inflammatory neuropathy in a patient on tumor necrosis factor-α antagonist therapy

We describe a patient on the tumor necrosis factor-α antagonist, adalimumab, for 2 years for rheumatoid arthitis, who developed a rapidly progressive inflammatory neuropathy shortly after starting oral steroids. Adalimumab was stopped at onset of neurologic symptoms. Electrophysiology showed demyelination, which persisted at 6 month follow-up, cerebrospinal fluid analysis showed persistent albuminocytologic dissociation, and magnetic resonance studies revealed enlarged and enhancing nerve roots. Treatment with intravenous immunoglobulins resulted in slow, progressive improvement. Tumor necrosis factor-α antagonists have previously been implicated in acquired demyelinating neuropathies. In this patient, we hypothesize that adalimumab may have caused an initially asymptomatic chronic inflammatory demyelinating polyneuropathy, which became symptomatic shortly after initiation of steroid therapy. This case may raise the issue of the safety of steroids in conjunction with antitumor necrosis factor-α therapy in susceptible patients.