Technical and clinical performance of the thermo-test device "Q-Sense" to assess small fibre function: A head-to-head comparison with the "Thermal Sensory Analyzer" TSA in diabetic patients and healthy volunteers.

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Thermo-test devices are rarely used outside specialized pain centres because of high acquisition costs. Recently, a new, portable device ("Q-Sense") was introduced, which is less expensive but has reduced cooling capacity (20°C). We assessed the reliability/validity of the "Q-Sense" by comparing it with the Thermal Sensory Analyzer (TSA). Using a phantom-skin model, the physical characteristics of both devices were compared. The clinical performance was assessed in a multicentre study by performing Quantitative Sensory Testing (QST) in 121 healthy volunteers and 83 diabetic patients (Eudra-Med-No. CIV-12-05-006501). Both device types showed ~40% slower temperature ramps for heating/cooling than nominal data. Cold/warm detection thresholds (CDT, WDT) and heat pain thresholds (HPT) of healthy subjects did not differ between device types. Cold pain thresholds (CPT) were biased for Q-Sense by a floor effect (p<.001). According to intraclass correlation coefficients (ICC), agreement between TSA and Q-Sense was good/excellent for CDT (ICC=0.894) and WDT (ICC=0.898), moderate for HPT (ICC=0.525) and poor for CPT (ICC=0.305). In diabetic patients, the sensitivity of Q-Sense to detect cold hypoesthesia was reduced in males >60years. Moderate correlations between thermal detection thresholds and morphological data from skin biopsies (n=51) were similar for both devices. Physical characteristics of both thermo-test devices are similarly limited by the poor temperature conduction of the skin. The Q-Sense is useful for thermal detection thresholds but of limited use for pain thresholds. For full clinical use, the lower cut-off temperature should be set to ≤18°C. High purchase costs prevent a widespread use of thermo-test devices for diagnosing small fibre neuropathy. The air-cooled "Q-Sense" could be a lower cost alternative, but its technical/clinical performance needs to be assessed because of its restricted cut-off for cooling (20°C). This study provides critical information on the physical characteristics and the clinical validity/reliability of the Q-Sense compared to the "Thermal Sensory Analyzer" (TSA). We recommend lowering the cut-off value of the Q-Sense to ≤18°C for its full clinical use.