Prurigo nodularis: systematic analysis of 58 histological criteria in 136 patients.

BACKGROUND: To date, there has been no systematic investigation of the detailed histological features of prurigo nodularis (PN) in a large cohort of patients.

METHODS: This retrospective study includes skin biopsies of 136 patients (63 males, 73 females; mean age: 58.38 years) with PN.

RESULTS: Highly characteristic for PN is the presence of thick compact orthohyperkeratosis; the hairy palm sign (folliculosebaceous units in nonvolar skin in conjunction with a thick and compact cornified layer, like that of volar skin); irregular epidermal hyperplasia or pseudoepitheliomatous hyperplasia; focal parakeratosis; hypergranulosis; fibrosis of the papillary dermis with vertically arranged collagen fibers; increased number of fibroblasts and capillaries; a superficial, perivascular and/or interstitial inflammatory infiltrate of lymphocytes, macrophages and, to a lesser extent, eosinophils and neutrophils. For comparison, histological findings in 45 patients (18 males, 27 females; mean, 55.64 years) with lichen simplex (LS) were studied. PN and LS, both of them scratch-induced, had 50 of 58 (86.2%) histological features in common.

CONCLUSIONS: PN revealed a characteristic histological pattern. Absence of pseudoepitheliomatous hyperplasia or nerve fiber thickening, however, does not rule out the histological diagnosis of PN. A correlation of clinical and histological findings is necessary to reliably distinguish between PN and LS.