Compressive neuropathies of the upper extremity: update on pathophysiology, classification, and electrodiagnostic findings

Abstract

Clinical examination and electrodiagnostic studies remain the gold standard for diagnosis of nerve injuries. Diagnosis of chronic nerve compression (CNC) injuries can be difficult in patients with confounding factors such as diabetes. The treatment of nerve entrapment ranges from medical to surgical management, depending on the nerve involved and on the severity and duration of compression. Considerable insights have been made at the molecular level, differentiating between nerve crush injuries and CNC injuries. Although the myelin changes after CNC injury were previously thought to be a mild form of Wallerian degeneration, recent evidence points to a distinct pathophysiology involving Schwann cell mechanosensitivity. Future areas of research include Schwann cell transplantation in the treatment regimen, the correlation between demyelination and the onset of pain, and the role of Schwann cell integrins in transducing the mechanical forces involved in nerve compression injuries to Schwann cells.

FIGURE 1

Integrin β4 relocalization following CNC injury. CNC-injured nerves show localization of integrin β4 (arrows) to SLIs as early as one week following injury. A Immunostaining of CNC-injured rat nerve at one week postcompression. B Normal nerves at the same timepoint. Red staining (phalloidin-TRITC) reveals F-actin localization at SLI’s, and green staining indicates integrin β4. Reprinted with permission from Pham K, Nassiri N, Gupta R. c-Jun, krox-20, and integrin β4 expression following chronic nerve compression injury. Neurosci Lett 2009;465:194–198. Copyright 2009, with permission from Elsevier.

FIGURE 2

Decreased nerve conduction velocity (NCV) in compressed nerves. Electrodiagnostic studies in both A rat models, and B murine models reveal decreased NCV (in m/s) following chronic nerve compression injury as compared to controls. C CMAP amplitudes are decreased slightly in CNC-injured nerves at 2 weeks, but the difference in CMAP amplitudes is not statistically significant, and the CMAP amplitudes recorded do not exhibit further declines. A and C are reproduced with permission from Mozaffar T, Strandberg E, Abe K, Hilgenberg LG, Smith MA, Gupta R. Neuromuscular junction integrity after chronic nerve compression injury. J Orthop Res 2009;27:114–119. Copyright 2009, with permission from Elsevier.