Tactile threshold detection in leprosy patients with an electronic algometer.

OBJECTIVE: To propose an electronic method for sensitivity evaluation in leprosy and to compare it to the Semmes-Weinstein monofilaments. METHODS: Thirty patients attending the Dermatology outpatient clinic of HCFMRP-USP were consecutively evaluated by both the electronic aesthesiometer and Semmes-Weinstein monofilaments on hand and foot test points. The intraclass correlation coefficient (ICC) was calculated to determine the variability of the electronic measures and the Kappa coefficient was calculated to determine the agreement between methods according to their categories (altered and non-altered tactile sensitivity). RESULTS: The ICC was approximately 1, demonstrating repeatability. The Kappa coefficient showed more than 75 and 63% agreement on the hand and foot points, respectively. The mean agreement between the 2 methods for the 7 points of the right and left hand was 77.14 and 75.71%, respectively. The mean agreement for all 10 points was 74.33 and 63.66% on the right and left foot, respectively. In cases of disagreement the detection of altered tactile sensitivity by the electronic esthesiometer on the right and left foot was 90.91 and 84.25%, respectively, with no detection by the monofilaments. CONCLUSION: The results suggest that the electronic esthesiometer is a reliable and easy application, capable of evaluating alterations of tactile sensitivity in leprosy patients.

Do nerve growth factor-related mechanisms contribute to loss of cutaneous nociception in leprosy?

While sensory loss in leprosy skin is the consequence of invasion by M. leprae of Schwann cells related to unmyelinated fibres, early loss of cutaneous pain sensation, even in the presence of nerve fibres and inflammation, is a hallmark of leprosy, and requires explanation. In normal skin, nerve growth factor (NGF) is produced by basal keratinocytes, and acts via its high affinity receptor (trk A) on nociceptor nerve fibres to increase their sensitivity, particularly in inflammation. We have therefore studied NGF- and trk A-like immunoreactivity in affected skin and mirror-site clinically-unaffected skin from patients with leprosy, and compared these with non-leprosy, control skin, following quantitative sensory testing at each site. Sensory tests were within normal limits in clinically-unaffected leprosy skin, but markedly abnormal in affected skin. Sub-epidermal PGP 9.5- and trk A- positive nerve fibres were reduced only in affected leprosy skin, with fewer fibres contacting keratinocytes. However, NGF-immunoreactivity in basal keratinocytes, and intra-epidermal PGP 9.5-positive nerve fibres, were reduced in both sites compared to non-leprosy controls, as were nerve fibres positive for the sensory neurone specific sodium channel SNS/PN3, which is regulated by NGF, and may mediate inflammation-induced hypersensitivity. Keratinocyte trk A expression (which mediates an autocrine role for NGF) was increased in clinically affected and unaffected skin, suggesting a compensatory mechanism secondary to reduced NGF secretion at both sites. We conclude that decreased NGF- and SNS/PN3-immunoreactivity, and loss of intra-epidermal innervation, may be found without sensory loss on quantitative testing in clinically-unaffected skin in leprosy; this appears to be a sub-clinical change, and may explain the lack of cutaneous pain with inflammation. Sensory loss occurred with reduced sub-epidermal nerve fibres in affected skin, but these still showed trk A-staining, suggesting NGF treatment may restore pain sensation.

Neurotrophins and peripheral neuropathy.

Endogenous nerve growth factor (NGF) levels were studied in patients with nerve trauma, diabetes mellitus and leprosy, the most common causes of human peripheral neuropathy. In diabetics, there was an early length-dependent dysfunction of small-diameter sensory fibres, with depletion of skin NGF and the sensory neuropeptide substance P. The NGF depletion correlated significantly with decreased skin axon-reflex vasodilatation, which is mediated by small sensory fibres at least partly via substance P release. Immunostaining showed depletion of NGF in keratinocytes in diabetic skin. In injured nerves, NGF levels were reduced when compared to intact nerve, except acutely distal to injury; NGF-immunostaining was seen in Schwann cells in distal segments, including neuromas. NGF levels were decreased in leprosy-affected skin and nerve. The role of neurotrophins in the rational treatment of human neuropathies is discussed e.g. loss of nociception and axon-reflex vasodilatation contribute to skin ulceration, a major and serious complication, for which NGF may provide prophylaxis.