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 (r(s)=0.450, p<0.001), neuropathic symptom score (r(s)=0.288, p=0.03), cold detection threshold (r(s)=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 >or=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.