Correlação entre densidade de fibras nervosas em biópsia de pele e teste de quantificação da sensibilidade térmica em pacientes com hanseníase

Abstract

It is known that, in lesions of leprosy, loss of tactile sensitivity, mediated by thick myelinated A-beta type nerve fibers, is preceded by the loss of thermal sensitivity, mediated by thin myelinated A-delta type and thin unmyelinated C type thin fibers, which makes the evaluation of the thermal sensitivity of a suspicious lesion a fundamental criterion for the leprosy diagnosis establishment. Recent studies involving thermal sensory testing have employed modern electronic instruments able to complete the quantitative sensory test (QST), the gold-standard method for the assessment of thermal sensitivity. In parallel, the morphological study of cutaneous innervation by means of special stains for intraepidermal and dermal nerve endings has become an alternative for assessing the impairment of these fine fibers involved in the thermal sensitivity. The few studies available in the literature that used the morphological study of thin cutaneous nerve fibers in leprosy patients noted a decrease in the density of dermo-epidermal thin fibers at the lesions of the disease and an association between this reduction and the increased thermal thresholds in the QST. These studies, however, did not specify important details about the methodology used in the QST and employed semi-quantitative methods for the evaluation of the cutaneous nerve fiber density, which limits its reproducibility. The present work aims to study the correlation between the degree of impairment of thermal sensitivity assessed by QST and the degree of decreased density of thin nerve fibers in the skin of leprosy patients. Twenty-two patients had skin lesions and contralateral clinically unaffected skin evaluated by biopsies and TQST, performed with the thermal sensory analyzer Thermal sensory analyzer TSA-II. The thin cutaneous nerve fibers were observed by immunohistochemical staining using anti- PGP 9.5 and quantified by morphometry. There were significant differences among lesions and contralateral unaffected skin in relation to cold, heat and pain induced by heat and cold detection thresholds. The mean absolute difference for these thermal thresholds were, respectively, 9.2 ° C, 6.0 ° C, 5.5 ° C and 4.2 ° C. The immunohistochemical staining of biopsies of lesions showed a significant thinning of intraepidermal and subepidermal fibers compared to contralateral unaffected skin biopsies. On average, the density of intraepidermal and subepidermal fibers showed a reduction of 79.5% (SD = 19.6) and 80.8% (SD = 24.9), respectively. We observed good correlation between intraepidermal and subepidermal fiber deficits. However, it was not possible to detect the correlation between the variables representing a deficit of cutaneous innervation and the variables representing a deficit of thermal sensitivity, since the thin fibers thinning was homogeneously intense in all patients, regardless of the degree of sensory deficit presented.