Chronic Lateral Epicondylalgia Does Not Exhibit Mechanical Pain Modulation in Response to Noxious Conditioning Heat Stimulus

Abstract

The impaired attenuation of pain by the application of a noxious conditioning stimulus at a segmentally distinct site, known as conditioned pain modulation, has been implicated in clinical pain states. Chronic lateral epicondylalgia (LE), which is characterized by lower pressure pain thresholds at sites remote to the affected elbow and spinal cord hyperexcitability, is a clinical pain state that might plausibly involve less efficacious conditioned pain modulation. This study aimed to determine if LE exhibits a less efficacious conditioned pain modulation compared to healthy controls. Twenty participants with LE, were aged 50.7 years (SD =7.05) and had their condition for 10.2 months (range 2-80) were matched by age and sex to 22 healthy participants. All participants indicated their pressure pain threshold (PPT) over the lateral epicondyle(s) before and during a conditioning noxious heat stimulus was applied over the calf. A conditioned pain modulation (CPM) score was calculated as the difference between the PPT before and during the heat pain-conditioning stimulus expressed as a percentage of PPT before the heat pain-conditioning stimulus. The condition (LE v Control) by Side (Affected v Unaffected) analysis of variance revealed a significant condition effect (p=0.001), but not side effect (p=0.192) or side by condition interaction effect (p=0.951). Follow up tests for the effect of condition revealed a mean deficit in CPM of -24.5% (95% confidence interval: -38.0 to -11.0) in LE compared to healthy participants. The results which suggest an impaired ability to modulate pain might be associated with the previously observed spinal cord hyperexcitability and the mechanical hyperalgesia that characterizes LE.