Chapter 3: Pathophysiology of Peripheral Nerve Injury

Objectives

On completion of this chapter, the student/practitioner will be able to:

• Relate the structural anatomy of the peripheral nerve to the etiologies of injury.

• Outline the role of cytokines in the inflammatory cascade of peripheral nerve injury.

• Define spinal cord sensitization as it relates to peripheral nerve injury.

• Define the local and systemic impact of peripheral nerve inflammation.

• Define “fibrosis” as it relates to peripheral nerve injury.

Key Terms

• Fibrosis

• Inflammation

• Neuropathy

• Overuse

Introduction

Neuropathies can result from mechanical trauma, such as shear or compressive forces on the nerve, particularly if repeated, and have been linked to the following risk factors: gender (female), advanced age, and reduced fitness.^1–4 Patients with median nerve neuropathy report symptoms such as pain in the hands and wrists or fingers that may travel into the forearm, elbow, and shoulder; paresthesias; numbness; and weakness.⁵ An objective diagnosis of median nerve dysfunction is typically based on electrophysiological evidence of slowed median nerve conduction localized to the wrist, although the combination of electrodiagnostic findings and symptom characteristics is reported to provide the most accurate diagnosis of carpal tunnel syndrome (CTS).²

Peripheral Nerve Damage and Inflammation With Overuse

Risk factors for the development of neuropathies include the performance of jobs characterized by repetitiveness, forcefulness, or awkward postures.^1,3,6,7 A relationship between advancing age and susceptibility to other risk factors for neuropathies has also been reported,^3,5,6,8 albeit one longitudinal study suggested that slowing of conduction in the median nerve occurs naturally with increasing age.⁴ CTS has the highest incidence rate of all occupation-related peripheral neuropathies, with 10,780 combined cases reported to the U.S. Occupational Safety and Health Administration in 2009 by private industry and state and local government, resulting in a median of 21 lost workdays per case. The overall CTS incidence rate affects 1 in 10,000 workers. Among female workers, CTS affects 1.5 in 10,000 workers, whereas among men, CTS affects 0.7 in 10,000 workers. The incidence rate for CTS was highest among workers 45 to 64 years old (1.5 in 10,000) compared with rates of 0.3 in 10,000 for workers 20 to 24 years old and 0.7 in 10,000 for workers 25 to 34 years old.⁶ In a 3-year prospective study of incidence in newly hired workers in computer-intensive jobs, computer operators older than age 30 showed an increased risk of developing neck, shoulder, arm, and hand symptoms, such as pain, aching, burning, numbness, or tingling.⁸ The most common disorder identified by the study relative to this population was somatic pain ...