See the (In)Visible: Infrared Thermography for Characterizing Thermal Patterns Associated with Peripheral Arterial Disease and Diabetes Mellitus

Background/Objectives: Peripheral arterial disease (PAD) and diabetes mellitus (DM) may produce different and overlapping plantar thermal patterns. This study descriptively characterized whole-foot temperature-distribution patterns in clinically defined healthy, PAD, DM, and combined PAD_DM cohorts. Methods: This single-center, exploratory, cross-sectional observational study included 73 participants: healthy controls (n = 21), isolated PAD (n = 13), isolated DM (n = 19), and combined PAD_DM (n = 20). Right- and left-foot temperature distributions were processed separately for each participant and interpreted as one paired bilateral thermal footprint using patient-level histograms, representative bilateral kernel density estimation (KDE) profiles, and a cohort-derived deterministic rule-based model. The model was developed from the present cohort and was not evaluated as an independent diagnostic classifier. Results: Among healthy controls, 11 of 21 participants (52.4%) were assigned to healthy and 8 of 21 (38.1%) to borderline healthy categories. In the DM cohort, 7 of 19 participants (36.8%) were assigned to DM, 3 of 19 (15.8%) to borderline healthy/suspected DM or controlled DM, 3 of 19 (15.8%) to DM suspected PAD, and 5 of 19 (26.3%) to PAD_DM. In the combined PAD_DM cohort, 15 of 20 participants (75.0%) were assigned to PAD_DM. The isolated PAD cohort was the most heterogeneous: 6 of 13 participants (46.2%) were assigned to PAD_DM, while none were assigned to the isolated PAD output. Conclusions: This exploratory, cross-sectional study demonstrated that whole-foot plantar temperature distributions can descriptively characterize differences among healthy individuals, patients with isolated DM, and those with combined PAD and DM. While healthy controls generally demonstrated symmetric thermal footprints, the DM cohort frequently exhibited globally elevated and compact temperature-distribution profiles, while mixed asymmetric patterns were common in participants with combined PAD and DM. In contrast, the isolated PAD cohort was characterized by pronounced thermal heterogeneity.