Objectives: To compare the pain numeric rating scale (NRS) and active cervical lateral flexion between diclofenac phonophoresis (DPP) and a conventional ultrasound therapy (UST) in treating myofascial pain syndrome (MPS).

Study design: A double-blinded randomized controlled trial.

Setting: Department of Physical Medicine and Rehabilitation, Taksin Hospital, Thailand.

Subjects: Fifty-two participants (41 females, 11 males, mean age 42 years, mean MPS duration 2 months) with myofascial pain syndrome at the upper trapezius muscle

Methods: Participants were allocated by block randomization into 2 groups, the UST Group (n = 26) treated with a conventional UST using a 1-MHz applicator, a standard coupling agent, stroke technique, continuous mode, intensity of 1 watt/cm2 for 10 minutes, and the DPP Group (n = 26) treated with the same UST technique but using a mixture of 4 grams of diclofenac gel and a standard coupling agent in a ratio of 1:4 instead of the standard coupling agent. Each participant was treated 3 times per week for 3 weeks for a total of 9 treatments. All participants rated their pain on a numeric rating scale (NRS). Active cervical lateral flexion was measured by an assessor prior to the initial treatment and following the final treatment. All participants and the assessor were blinded to the treatments received.

Results: Before the treatments, there was no statistically significance in NRS (p = 1.00) or active cervical lateral flexion (p = 0.75) between the two groups. After the treatments, NRS of the DPP group was significantly lower than the UST group (p = 0.03). However, active cervical lateral flexion was not significantly different between the groups (p = 0.29). Group analysis found that NRS was significantly reduced, by 2.58 in the UST group (p = 0.00)

and by 3.46 in the DPP group (p = 0.00). Active cervical lateral flexion motion was significantly increased in the DPP group (p =0.02) but not in UST group (p = 0.08) after the 3-week therapy.

Conclusions: Diclofenac phonophoresis can reduce pain in myofascial pain syndrome at upper trapezius muscle better than conventional ultrasound therapy.