Heat-sensitive conduction block in ulnar neuropathy at the elbow

Objectives: To study the effects of elbow heating on conduction block (CB) and across-elbow conduction velocity (CV) in patients with ulnar neuropathy at the elbow (UNE). Methods: We studied 15 patients with UNE, performing motor nerve conduction studies at 32°C and after heating the elbow to 42°C. Results: At 32°C, mean response amplitude and area with above-elbow (AE) stimulation were 20.4 and 16.0% lower than with below-elbow (BE) stimulation, respectively. With heating the elbow to 42°C, these differences increased significantly to 28.9 and 26.9% (P=0.019 and 0.029), respectively. The mean CV reduction in the across-elbow segment relative to the forearm segment also increased from 20.5 m/s at 32°C to 25.6 m/s at 42°C (P=0.0010). Across-elbow CV at 32°C correlated with increased CB (as measured by amplitude) with heating (r=0.53, P=0.048) and approached significance for area (r=0.48, P=0.068) Likewise, baseline CB at 32°C correlated with the likelihood of increased CB for amplitude (r=0.77, P<0.001), and approached significance for area (r=0.47, P=0.079). Conclusions: Elbow heating in UNE increases the relative drop in across-elbow CV and the degree of across-elbow CB; absolute across-elbow CV and the presence of baseline CB at 32°C are good predictors of this latter effect.