Properties of human skin mechanoreceptors in peripheral neuropathy

Objectives: To investigate the properties of mechanoreceptors in patients with peripheral neuropathy. The skin mechanoreceptor is a terminal organ of the primary sensory neuron, which is likely to be affected earlier and more severely than is the nerve trunk by peripheral neuropathies. Methods: Single sensory unit responses to air-puff and electric stimulation were recorded using the microneurographic technique in the glabrous skin of the hand. Receptor transduction time was estimated by a latency difference between electric- and air-puff-induced responses. Results: A total of 38 mechanoreceptive units were obtained from 14 normal subjects. All the units responded to air-puff stimuli irrespective of the receptor type, and receptor transduction time was approximately 2 ms. A total of 32 units were recorded from 11 patients with neuropathy of variable causes. Seven (22%) of the 32 neuropathic units did not respond to air-puffs despite their ability to respond to electric stimulation. Compared to normal ones, units from patients with peripheral neuropathy had significantly higher mechanical thresholds, but receptor transduction times did not differ significantly. Conclusions: Changes in receptor properties in human neuropathy are characterized by increased mechanical threshold without prolongation of receptor transduction time, possibly due to a high threshold for generating receptor potentials.