Bilateral myofascial trigger points in the forearm muscles in patients with chronic unilateral lateral epicondylalgia: a blinded, controlled study.

Objective: The aim of the present study was to investigate the presence of active and latent muscle trigger points (TrPs) in the forearm musculature on both affected and unaffected sides in patients with lateral epicondylalgia (LE) and healthy controls.
Methods: Twenty-five patients with LE and 20 healthy matched controls participated. Both groups were examined for the presence of TrPs in the extensor carpi radialis brevis, extensor carpi radialis longus, extensor digitorum communis, and brachioradialis muscles in a blinded fashion. TrPs were identified in both affected and unaffected sides within the patient group. In the control group, TrPs were explored around the dominant side. Pressure pain thresholds (PPTs) were assessed on both affected and unaffected arms.
Results: In the patient group, the number of active muscle TrPs in the affected side was 3.1 [95% confidence interval (CI): 2.8-3.4], whereas in the unaffected arm, only latent TrPs were found (mean: 2.2; 95% CI: 1.8-2.6). Active TrPs were only located on the affected side (P<0.001). Within the control group, the number of latent TrPs in the dominant arm was 0.4 (95% CI: 0.0-0.7), which was significantly lower than the number of latent TrPs in the unaffected arm (P<0.001) in patients. Therefore, latent muscle TrPs in the forearm musculature were associated with the unaffected side in the patient group as compared with the dominant arm in healthy controls: extensor carpi radialis brevis [odds ratio (OR)=66 (95% CI: 9.9-48.8)], extensor carpi radialis longus [OR=16 (95% CI: 3.7-29.6)], brachioradialis [OR=2.6 (95% CI: 0.3-27.1)], and extensor digitorum communis [OR=0.5 (95% CI: 0.4-0.8)]. PPTs were lower around the affected side than around the unaffected arm in patients (mean+/-SD: 274.5+/-90.4 KPa vs. 465.4+/-140.7 KPa; P<0.001) in the patient group. Finally, PPT from the extensor digitorum muscle in those patients with active TrPs (mean+/-SD: 244+/-70.4 KPa) was significantly lower (P<0.001) than PPT levels of patients with no TrP in the same muscle (mean+/-SD: 370+/-83.4 KPa).
Conclusions: Latent TrPs are present in forearm muscles on the unaffected side in patients with LE where active TrPs contribute to the pain on the affected arm. The presence of latent TrPs on the unaffected side in unilateral LE may be related to central sensitization and be a mechanism explaining bilateral pain in some patients with unilateral pathologies.