A case control study examining the population of epidermal and dermal pathology, inflammatory infiltrate and neural milieu of primary prurigo nodularis using S-100 and Toluidine blue stain and its therapeutic implications

A cross-sectional observational study was in cases of untreated primary prurigo nodularis cases with histopathological assessment in 49 cases of prurigo from lesional and non lesional uninvolved skin with assessment of epidermal and dermal changes, composition of dermal infiltrate and S-100 & toluidine blue staining to assess the role of nerve and mast cells. The most common histological changes seen in lesional skin were hyperkeratosis( 98%), irregular hyperplasis (69.4%) hypergranulosis (69.4%), sub epidermal clefting( 6%), vertical collagen bundles (51.0%) & dermal fibrosis (48.9%). Chronic inflammatory infiltrate was seen in all cases (100%) and the most common inflammatory cells seen being found were lymphocytes (100%) followed by, eosinophils (18.4%), plasma cells (8.2%) patients neutrophils. (2.0%). There was a marked increase in the expression of S-100 (6.92 ± 3.40 Vs 3.94 ± 2.15, p < 0.001) and toludidine blue (4.99 ± 4.47 Vs 1.22 ± 1.28, p < 0.001) in the lesional skin as compared to the non lesional skin. Thus we can infer that the epidermal and dermal pathology is dependent on lymphocytes, mast cells and neural hyperplasia which perpetuate the pathology of PN by triggering the itch-inflammation cycle. Thus apart from immunosuppressive agents that target lymphocytes and their cytokines therapy targeted at mast cells and neural proliferation may be needed to treat prurigo nodularis.