Clinical characteristics of unilateral and bilateral masticatory myofascial pain: an exploratory cross-sectional study.

BACKGROUND: The aim of the present study was to characterize the distribution of unilateral and bilateral masticatory pain in patients with a diagnosis of masticatory myofascial pain (MMP) examined in a tertiary orofacial pain clinic sample and to compare baseline demographic, pain-related, and palpation-tenderness characteristics between these presentations. METHODS: Patients diagnosed with MMP were included. The pain history documented reported pain laterality (unilateral; bilateral with equal intensity; bilateral with one side predominant), quality, severity, associated features, pain spread, temporal pattern, pain intensity using a 0-10 verbal pain scale (VPS), and pain-related awakening from sleep. Additionally, muscle and TMJ tenderness to palpation was scored on a 0-3 scale. Side-to-side asymmetry for each masticatory muscle was calculated as the absolute difference between right- and left-side tenderness scores (delta). Categorical variables were compared using Chi-square, Fisher's exact, or Fisher- Freeman-Halton tests, as appropriate. Quantitative variables were analyzed using exact Mann- Whitney U tests and summarized as medians and interquartile ranges. A two-sided p value <0.05 was considered significant. RESULTS: Forty-three patients were included (11 males, 32 females). Unilateral pain was reported by 37% (n=16), bilateral pain by 35% (n=15), and bilateral pain with side predominance by 28% (n=12). The two bilateral groups detected no clear differences in this small sample in palpation asymmetry and were combined into one bilateral group. Palpation asymmetry (delta) was significantly greater in unilateral compared with bilateral presentations across masticatory muscles (p<0.001). Unilateral MMP was significantly associated with shorter time since pain onset (p<0.002), older age group (p<0.01), smaller TMJ index (p<0.026) and pain on contralateral loading (0.004), pain spread was smaller but did not reach significance. CONCLUSIONS: Unilateral MMP showed different baseline clinical patterns with greater side-toside palpation asymmetry and shorter time since pain onset compared to bilateral MMP. These findings support the clinical value of recording laterality in MMP for future research, but do not establish temporal progression or distinct pathophysiological phenotypes.