The diagnostic signature of diabetic enthesopathy: bilateral symmetry, serological silence, and ultrasound dominance.

Abstract

Objective: To characterize the distinctive bilateral, serological, and radiographic phenotype of diabetic enthesopathy using standardized quantitative ultrasonography with validated cutoff thresholds.

Methods: This cross-sectional extended analysis of a previously published cohort enrolled 60 patients with diabetes (17 T1DM, 43 T2DM). Five bilateral entheseal sites were evaluated using the Glasgow Ultrasound Enthesitis Scoring System (GUESS) methodology with validated thickness cutoffs (> 6.1 mm quadriceps, >4.0 mm patellar, >5.2 mm Achilles, >4.4 mm plantar fascia). Rheumatoid factor (RF), anti-CCP, erythrocyte sedimentation rate (ESR), serum uric acid, and inflammatory ratios (NLR, PLR) were assessed. Conventional hand, foot, and knee radiographs were reviewed. Multiple linear regression with bootstrap validation (2000 iterations) identified independent predictors of structural burden.

Results: Mean total entheseal thickness was 4.82±0.50 mm. All sites demonstrated strong bilateral symmetry with excellent inter-side correlations (r=0.49-0.60, all p<0.001) and no significant paired differences. RF was positive in 5.0% and anti-CCP in 0%; inflammatory indices were normal, and serum uric acid showed neither a significant intergroup difference nor an independent association with entheseal thickness (hyperuricemia prevalence 13.3%). Ultrasound detected tendon thickening in 93.3%, enthesophytes in 78.3%, and bursitis in 60.0%, whereas radiography showed only degenerative changes with <5% entheseal-specific findings. Age was the sole independent predictor of mean thickness (β=+0.020; p=0.007). After adjustment, the T2DM coefficient was borderline non-significant (β=-0.467; p=0.056), indicating that the higher raw burden in T2DM is primarily explained by age rather than diabetes subtype.

Conclusion: Diabetic enthesopathy exhibits a distinct "metabolic-mechanical" phenotype defined by striking bilateral symmetry, near-complete seronegativity, and ultrasound-dominant structural detection. The increased burden in T2DM is predominantly age-mediated, with a borderline independent effect warranting larger confirmatory studies. Musculoskeletal ultrasound should be prioritized in older diabetic patients for early detection of subclinical entheseal pathology, irrespective of diabetes type.