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.