Tongue Characteristics and Musculoskeletal Pain in Patients with Type 2 Diabetes Mellitus: A Principal Component and Latent Profile Analysis.

PURPOSE: We investigated the association between tongue characteristics and musculoskeletal (MSK) pain in patients with type 2 diabetes mellitus (T2DM) and explored potential noninvasive tongue-based biomarkers. PATIENTS AND METHODS: This cross-sectional study enrolled 586 patients with T2DM (420 without and 166 with MSK pain) between January 2023 and December 2024 at the Second Affiliated Hospital of Tianjin University of Traditional Chinese Medicine. Tongue images were obtained using a standardized tongue-imaging device. Color parameters in the Lab and RGB color spaces were extracted from the tongue proper and coating. Multivariate logistic regression was used to examine associations between individual tongue parameters and MSK pain. Principal component analysis was applied separately to tongue proper and coating parameters to derive composite scores, and latent profile analysis (LPA) was used to identify tongue-based subgroups. RESULTS: After adjustment for confounders, higher TC-b (Odds ratio [OR], 1.26; 95% confidence interval [CI], 1.151-1.379; P<0.001) and CC-b (OR, 1.199; 95% CI, 1.111-1.294; P<0.001) values were significantly associated with an increased risk of MSK pain. The tongue-proper composite score was positively associated with MSK pain risk (OR, 1.649; 95% CI, 1.240-2.193; P<0.001), whereas the tongue-coating composite score showed a negative association (OR, 0.586; 95% CI, 0.425-0.807; P=0.001). LPA identified five distinct tongue-imaging subgroups, including one subgroup with high TC-b and CC-b that exhibited a significantly higher risk of MSK pain. CONCLUSION: Tongue color characteristics are associated with MSK pain in patients with T2DM and may serve as potential noninvasive biomarkers for the auxiliary assessment of MSK pain. Prospective studies are needed to clarify their clinical relevance and potential utility.