Efficacy and side effects of diclofenac patch in treatment of patients with myofascial pain syndrome of the upper trapezius.

Locally administered nonsteroidal anti-inflammatory drugs have been widely used in acute soft-tissue damage and articular musculoskeletal pain. This double-blind, placebo-controlled, randomized study was designed to evaluate the efficacy and safety of a topical diclofenac sodium patch in the relief of pain and inflammation as a result of myofascial pain syndrome (MPS) in the upper trapezius. After sample size calculations indicated that 147 patients would be needed to detect a 25% difference between drug and control, 153 patients with MPS were recruited and randomized to receive either a diclofenac sodium patch or control (menthol) patch. Visual analog scale (VAS), cervical active range of motion, pressure pain threshold of the myofascial trigger point (MTrP), patient global assessment, Neck Disability Index, and the occurrence of adverse events were assessed on Day 0 (baseline), Day 4, and Day 8. Use of the diclofenac sodium patch elicited favorable responses for the VAS, cervical active range of motion, and Neck Disability Index by the end of the treatment course (P<0.05), and was consistently superior to the control patch at all time intervals. No significant differences were observed for the pressure pain threshold of the MTrP for either patch. Tolerability assessment similarly showed the diclofenac patch to be comparatively superior. When assessed at the end of the study, 20 diclofenac patch patients, but only four control patients, considered the tolerability of treatment to be "very good." Significant differences in adverse reactions were observed between the diclofenac and control patches, with the control patch more likely to produce overall skin irritation. This study demonstrate that the diclofenac sodium patch was superior to the control patch in terms of reducing pain and improving functional outcomes, and did not result in significant adverse effects.