Effect of phonophoresis of hydrocortisone and Dimethyl sulfoxide (DMSO) on latent trigger points of upper trapezius muscle

Myofascial trigger points are one of the most common causes of musculoskeletal pain. Phonophoresis is the use of ultrasound to enhance drug absorption through the skin and may be useful for treating trigger point; however, there is little information about the mechanisms of it. Hydrocortisone is one of the corticosteroid medications that can be used for phonophoresis. As Dimethyl sulfoxide (DMSO) increases the permeability of drugs through the skin by changing the configuration of the horny skin cells and intercellular keratin, it may intensify the effects of hydrocortisone. The purpose of this study was to investigate the effect of phonophoresis of combined hydrocortisone and DMSO on pain intensity (VAS), pressure pain threshold of trigger points (PPT) and range of motion of neck (ILF, CLF) in participants with latent trigger points of upper trapezius muscle. Forty subjects with latent trigger point of upper trapezius were randomly divided into 2 treatment groups: Phonophoresis with hydrocortisone %1 and phonophoresis with combined hydrocortisone %1 and DMSO %10. The treatment consisted of 10 sessions and the outcomes were evaluated before the treatment, the end of the 5th and 10th sessions and 2 weeks after the last session. Both treatments showed improved intensity of pain (VAS), pressure pain threshold (PPT), ipsi-lateral flexion (ILF), counter-lateral flexion (CLF) (p<0.001), but there was no significant differences between the intervention groups. However, only the effects of the combined gel remained stable after 2-week follow-up (p<0.05). Results showed that there is no preference between the two gels, but adding DMSO may increase the long-term effects of hydrocortisone.