Diagnostic accuracy of quantitative sensory testing for detecting small fiber impairment in polyneuropathy and diagnosing small fiber neuropathy

This cross-sectional retrospective study evaluated the diagnostic accuracy of cold detection thresholds (CDT) and warm detection thresholds (WDT), measured by quantitative sensory testing, for detecting small fiber impairment in polyneuropathy and diagnosing small fiber neuropathy (SFN). A total of 384 individuals with distally distributed sensory disturbances were included. Using ACTTION criteria, 138 patients with polyneuropathy were identified. Among them, 36 were diagnosed with SFN, 91 with mixed fiber polyneuropathy, and 11 with pure large fiber polyneuropathy. First, we assessed CDT and WDT accuracy, both individually and combined (ie, an abnormal value in either CDT or WDT), in detecting small fiber impairment in polyneuropathy. Next, we calculated CDT and WDT diagnostic accuracy for SFN, both alone and combined, and evaluated their accuracy when integrated with small fiber-related clinical abnormalities. Isolated abnormalities in CDT or WDT showed relatively low diagnostic accuracy. However, combined abnormalities achieved a sensitivity of 69% and specificity of 70% for detecting small fiber impairment in distal symmetric polyneuropathy. For SFN diagnosis, combining CDT and WDT yielded 78% sensitivity, 70% specificity, and a 94% negative predictive value. These metrics improved to 78% sensitivity and 100% specificity when CDT or WDT were integrated with small-fiber-related clinical abnormalities. Although individual CDT and WDT assessments offer limited diagnostic accuracy, their combination provides a practical, noninvasive approach for screening small fiber impairment in distal symmetric polyneuropathy and diagnosing SFN. This strategy may reduce the need for more invasive and less cost-effective procedures, like skin biopsy.