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Carpal Tunnel Syndrome (CTS) is one of the most common peripheral entrapment neuropathies, resulting from compression of the median nerve within the carpal tunnel at the wrist. This condition is frequently associated with pain, reduced grip strength, and impaired fine motor control of the hand. Early diagnosis of CTS remains challenging, as conventional clinical and electrophysiological assessments often detect changes only after significant nerve dysfunction has occurred. Therefore, there is a need for sensitive, non-invasive techniques capable of identifying early functional alterations before irreversible damage develops. The abductor pollicis brevis (APB) muscle, which plays a critical role in thumb abduction and opposition, is innervated exclusively by the median nerve and is among the first muscles affected in CTS. Alterations in the thermal and mechanical properties of this muscle may reflect early neurovascular and neuromuscular disturbances associated with median nerve compromise. Infrared (IR) thermography has gained attention as a non-contact imaging modality that captures skin temperature distribution, providing indirect information about microcirculatory changes, autonomic regulation, and muscle activity. In parallel, myotonometry enables objective quantification of intrinsic muscle properties, such as dynamic stiffness, tone, and elasticity, offering insight into neuromuscular adaptations under different physiological conditions.
The present study aimed to investigate the thermal behaviour of the APB muscle in response to cold stress and to evaluate concurrent changes in myotonometric parameters in healthy individuals. Establishing normative reference data in asymptomatic subjects is an essential step toward identifying deviations associated with CTS pathology. IR thermal imaging of the palmar region was conducted on 10 healthy subjects under controlled laboratory conditions. Baseline thermal images were acquired at rest, followed by a standardized cold stress protocol involving hand immersion in water at 12°C for 5 minutes. Thermal images were recorded immediately after cold exposure to assess acute temperature changes. Myotonometric measurements of the APB muscle were obtained before and after cold stress to evaluate variations in muscle properties. Preliminary analysis revealed a significant reduction in the average temperature of the APB muscle following cold stress, consistent with vasoconstriction. Recovery patterns varied across subjects, with some showing rapid rewarming while others exhibited delayed thermal normalization. Myotonometric measurements showed increased stiffness following cold stress, suggesting a transient neuromuscular adaptation. These results underscore the APB muscle's sensitivity to both thermal and mechanical changes induced by cold stress. It is observed that IR thermography combined with myotonometry could provide a non-invasive approach to characterizing APB muscle responses. As establishing baseline characteristics in healthy individuals is crucial for early diagnosis, this study seems to be clinically useful.
