Effects of intramuscular morphine in men and women with temporomandibular disorder with myofascial pain

Abstract

Objectives: This placebo-controlled randomized double-blinded clinical study assessed the analgesic efficacy of intramuscular morphine in TMD patients with myofascial pain and sex-dependent responses of the morphine treatment.

Subjects and methods: Men and women with TMD were treated with morphine (1.5 or 5 mg), lidocaine, or saline in the masseter muscle. VAS of pain intensity, PPT, and PPtol were compared between treatment groups and gender. An additional group was treated with morphine in the trapezius muscle to evaluate the systemic effect of morphine that may reduce pain in the masseter muscle.

Results: There was a significant difference in VAS scores between the morphine 5 mg group and the saline group favoring morphine, but not between the morphine 5 mg and lidocaine. Morphine 1.5 and 5 mg treatments led to consistently and significantly elevated PPT and PPtol measures in men, but not in women. Morphine administered in the trapezius muscle did not affect the outcome measures.

Conclusion: A single dose intramuscular morphine produced analgesic effects up to 48 hr in patients with myofascial pain. Intramuscular morphine elevated mechanical pain threshold and tolerance in the masseter only in male patients, suggesting sex differences in local morphine effects. No systemic effect of intramuscular morphine was detected.

Keywords: masseter; muscle pain; opioid receptor; peripheral; trigeminal.

Figure 1

Effects of intramuscular treatments on (A) VAS scores, (B) PPT and (C) PPtol measures. Data were normalized to the baseline scores for each participant. Mean percent changes in the VAS scores, PPT and PPtol measures were plotted against time and compared between saline and morphine treatment conditions. * denotes significant treatment effect between morphine 5 mg and saline groups. # denotes significant changes compared to the baseline values for all three treatment groups over time. The data are represented as mean ± SEM.

Figure 2

Effects of intra-masseter lidocaine on VAS scores (A), PPT (B) and PPtol (C) measures. Effects of morphine 5 mg shown in Fig 1 were re-plotted here for comparison. Mean percent changes in the VAS scores, PPT and PPtol measures assessed from the masseter muscle were plotted against time. # denotes significant changes compared to the baseline values only for lidocaine group. Effects of intra-trapezius morphine 5 mg on changes in the VAS scores (D), PPT(E) and PPtol (F) measures assessed from the masseter muscle. The data are represented as mean ± SEM. Trpz, trapezius

Figure 3

Mean percent changes in VAS scores (A–C), PPT measures (D–F), and PPtol measures (G–I) were plotted against time and compared between men and women for saline, morphine 1.5 mg, and morphine 5 mg treatment condition. # denotes significant changes in VAS scores compared to the baseline values. * denotes significant difference between men and women. The data are represented as mean ± SEM.