AbstractIntroduction:There are three main potential mechanisms of recovery after nerve lesion: (1) resolution of conduction block, (2) collateral reinnervation, and (3) nerve regeneration. Their relative contributions in recovery after focal neuropathies are not well established.Methods:In a group of previously reported prospective cohort of patients with ulnar neuropathy at the elbow (UNE), I performed a post-hoc analysis of their clinical and electrodiagnostic findings. I compared amplitudes of the compound muscle action potential (CMAP) and sensory nerve action potential (SNAP) on ulnar nerve stimulation, as well as qualitative concentric needle electromyography (EMG) findings in the abductor digiti minimi muscle on the initial and follow-up examinations several years later.Results:Altogether, 111 UNE patients (114 arms) were studied. During median follow-up period of 880 days (range: 385–1545 days), CMAP amplitude increased (p= 0.02), and conduction block in the elbow segment recovered (from median 17% to 7%;p< 0.001). By contrast, SNAP amplitude did not change (p= 0.89). On needle EMG, spontaneous denervation activity diminished (p< 0.001), motor unit potential (MUP) amplitude increased (p< 0.001), and MUP recruitment remained unchanged (p= 0.43).Conclusions:Findings of the present study indicate that nerve function in chronic focal compression/entrapment neuropathies seems to improve mainly due to the resolution of the conduction block and collateral reinnervation. Contribution of nerve regeneration seems to be minor; the majority of axons lost in chronic focal neuropathies probably never recover. Further studies using quantitative methods are needed to validate present findings.