A new device to quantify tactile sensation in neuropathy.

OBJECTIVE: To devise a rapid, sensitive method to quantify tactile threshold of finger pads for early detection and staging of peripheral neuropathy and for use in clinical trials. METHODS: Subjects were 166 healthy controls and 103 patients with, or at risk for, peripheral neuropathy. Subjects were screened by questionnaire. The test device, the Bumps, is a checkerboard-like smooth surface with 12 squares; each square encloses 5 colored circles. The subject explores the circles of each square with the index finger pad to locate the one circle containing a small bump. Bumps in different squares have different heights. Detection threshold is defined as the smallest bump height detected. In some subjects, a 3-mm skin biopsy from the tested finger pad was taken to compare density of Meissner corpuscles (MCs) to bump detection thresholds. RESULTS: The mean (±SEM) bump detection threshold for control subjects was 3.3 ± 0.10 µm. Threshold and test time were age related, older subjects having slightly higher thresholds and using more time. Mean detection threshold of patients with neuropathy (6.2 ± 0.35 µm) differed from controls (p < 0.001). A proposed threshold for identifying impaired sensation had a sensitivity of 71% and specificity of 74%. Detection threshold was higher when MC density was decreased. CONCLUSIONS: These preliminary studies suggest that the Bumps test is a rapid, sensitive, inexpensive method to quantify tactile sensation of finger pads. It has potential for early diagnosis of tactile deficiency in subjects suspected of having neuropathy, for staging degree of tactile deficit, and for monitoring change over time.