Modulatory effects on axonal function after intravenous immunoglobulin therapy in chronic inflammatory demyelinating polyneuropathy.

OBJECTIVE: To investigate the immediate and longitudinal mechanisms of action of intravenous immunoglobulin (IVIg) on axonal function in chronic inflammatory demyelinating polyneuropathy (CIDP).
DESIGN: Prospective single-center study.
SETTING: Hospitals and outpatient clinics. PARTICIPANTS: Clinical and functional assessment, nerve conduction studies, and 526 motor excitability studies were undertaken in 27 patients, matched before and immediately after infusion and followed up longitudinally. MAIN OUTCOME MEASURES: Axonal excitability variables were measured before and immediately after infusion and compared with matched studies and findings in healthy controls.
RESULTS: Immediately after infusion, patients demonstrated decreased threshold, with significant reduction in strength-duration time constant (P = .003), reduction in accommodation to depolarization (P = .04), and reduced threshold change during hyperpolarization (P = .003), accompanied by significant decreases in superexcitability (P = .03) and subexcitability (P = .02). In contrast, changes were absent in disease controls, confirming a specific IVIg action in CIDP patients. Longitudinally, changes correlated with clinical improvement (mean [SE] increase in the Medical Research Council sum score, 2.7 [0.7]; P = .005). Increased compound muscle action potential amplitude was associated with reduction in terminal latency (correlation coefficient, -0.65; P = .02). In addition, these changes translated into improvement in functional assessment with the adjusted Inflammatory Neuropathy Cause and Treatment score, which demonstrated a significant correlation with nerve excitability variables longitudinally (P = .01).
CONCLUSIONS: Findings from the present series establish a modulatory effect of IVIg on axonal function in CIDP patients, suggesting that IVIg stabilizes axonal membrane potential and promotes axonal recovery.