Infrared Thermography for Detection of Neural Impairment in Leprosy: A Cross-Sectional Study.

Background
Leprosy, caused by Mycobacterium leprae, leads to peripheral neuropathy and significant functional disability if its diagnosis is delayed. Infrared thermography may offer a non-invasive method for the detection of neurological complications.
Methods
A cross-sectional study was conducted with 100 leprosy patients and 20 healthy controls. Participants were assessed for cutaneous temperature using infrared thermography at defined areas corresponding to peripheral nerve innervation points (hands, feet, and face). Sensory neuropathy was analyzed using the Semmes-Weinstein (SW) monofilament test, while autonomic nerve dysfunction was evaluated through the sympathetic skin response (SSR). Data were analyzed with the aim of verifying whether changes in skin temperature clinically correlated with sensory loss, autonomic nerve dysfunction, and distinct forms of the leprosy spectrum.
Results
Leprosy patients had significantly lower skin temperature compared to controls, with a mean temperature of 32.5°C ± 2.3°C vs. 35.2°C ± 0.4°C for hands (p < 0.001) and 24.1°C ± 2.8°C vs. 34.8°C ± 0.5°C for feet (p < 0.001). Temperature differences were most pronounced in body areas showing sensory neuropathy (e.g., 30.1°C ± 2.2°C for hands with absent sensation vs. 34.1°C ± 1.6°C with normal sensation, p < 0.001). Strong linear correlations were found between cutaneous temperature and sensory loss assessed using SW filaments (p < 0.001) and between cutaneous temperature and SSR (p < 0.001). Disability grade also correlated with lower temperatures, with hands at 34.3°C for no disability, 31.3°C for Grade 1, and 31.5°C for Grade 2 disability.
Conclusion
Infrared thermography is a promising, non-invasive tool for the detection of peripheral sensory impairment in leprosy. The results obtained by infrared thermography show a strong correlation with those obtained using standard tests for sensory loss and autonomic nerve dysfunction.