Clinicopathological Differences between Acquired Reactive Perforating Collagenosis and Prurigo Nodularis

Background: Acquired reactive perforating collagenosis (ARPC) is a skin disease characterized by multiple itchy nodules, which is notably similar to the skin eruptions of prurigo nodularis (PN). The aim of this study was to prove the clinicopathological differences between ARPC and PN. Methods: We examined 22 patients with ARPC (6 males and 16 females) and 38 patients with PN (27 males and 11 females), diagnosed clinically and histologically. Transepidermal elimination of collagen which is characteristic histological findings for ARPC was found in all ARPC patients, but not in PN patients even in a serial section. Clinical findings, laboratory data, histological findings, immunohistochemical results, and efficacy of the therapies were compared between the two groups. Results: On evaluation of laboratory data, thymus and activation-regulated chemokine (TARC) levels and peripheral eosinophil counts were lower in ARPC than in PN. Histologically, we observed greater infiltration of neutrophils, histiocytes, and lymphocytes and more extensive capillaries in ARPC than in PN. Upon immunohistochemical analysis, CD163+ macrophages were found to be more abundant in the upper-to-deep dermis of ARPC, and both CD4+ T cells and CD8+ T cells were significantly increased in the mid-to-deep dermis of ARPC. The efficacies of topical steroid and antihistamines were improved by the addition of emollients in ARPC. Conclusion: This is the first report to show the histological differences in cell infiltration between the lesions of ARPC and PN. It is likely that inflammation mediated by neutrophils and M2 macrophages may be involved in the formation of ARPC lesions, as against PN lesions mediated by epidermal changes such as spongiosis. It is suggested that the addition of emollients can increase the efficacy of treatments for ARPC. However, further studies are necessary to define the precise pathomechanisms of ARPC and the effects of emollients on ARPC.