The Neuropad test: A visual indicator test for human diabetic neuropathy

Abstract

Aims/hypothesis: The commercially available Neuropad test was developed as a simple visual indicator test to evaluate diabetic neuropathy. It uses a colour change to define the integrity of skin sympathetic cholinergic innervation. We compared the results of Neuropad assessment in the foot with established measures of somatic and autonomic neuropathy. Methods: Fifty-seven diabetic patients underwent Neuropad assessment, quantitative sensory and autonomic function testing, and evaluation of intra-epidermal nerve fibre density in foot skin biopsies. Results: Neuropad responses correlated with the neuropathy disability score (rs=0.450, p<0.001), neuropathic symptom score (rs=0.288, p=0.03), cold detection threshold (rs=0.394, p=0.003), heat-as-pain perception threshold visual analogue score 0.5 (r s=0.279, p=0.043) and deep-breathing heart rate variability (r s=-0.525, p<0.001). Intra-epidermal nerve fibre density (fibres/mm) compared with age- and sex-matched control subjects (11.06±0.82) was non-significantly reduced (7.37±0.93) in diabetic patients with a normal Neuropad response and significantly reduced in patients with a patchy (5.01±0.93) or absent (5.02±0.77) response (p=0.02). The sensitivity of an abnormal Neuropad response in detecting clinical neuropathy (neuropathy disability score ≥5) was 85% (negative predictive value 71%) and the specificity was 45% (positive predictive value 69%). Conclusions/interpretation: The Neuropad test may be a simple indicator for screening patients with diabetic neuropathy. © 2008 Springer-Verlag.