Figure 1. Left median motor nerve conduction (MNC) study. Conduction block (arrow) is demonstrated on the left screen with more than 50% decrease in CMAP amplitude at proximal site (elbow 3.3 mV) when compared to distal site (wrist 11.1 mV). The right screen shows resolution of conduction block after several months of IVIG (CMAP amplitude at wrist (13.2 mV) and elbow (12.8 mV)). There is also improvement of motor distal latency onset from 4.6 ms to 3.4 ms over the 6-month period. CMAP: compound muscle action potential; IVIG: intravenous immunoglobulin; APB: abductor pollicis brevis.