Tracing the clinicodermoscopic and histopathological evolution of acquired reactive perforating collagenosis: a case report.

Acquired reactive perforating collagenosis (ARPC) is a rare perforating dermatosis that is frequently misdiagnosed, particularly before the development of overt transepidermal elimination. Although early lesions have been sporadically mentioned in previous reports, direct clinicopathological evidence supporting a recognizable pre-perforating stage remains limited. We report the case of a 64-year-old woman with a 3-year history of progressive, generalized pruritic papules and nodules, initially misdiagnosed as eczema and refractory to conventional treatments. The patient had long-standing type 2 diabetes mellitus and other metabolic comorbidities. Dermoscopy of early erythematous papules revealed subtle but reproducible features distinct from those of fully developed lesions. Notably, even in early lesions showing focal epidermal disruption, classic dermoscopic signs of perforation were absent. Targeted biopsy of these early lesions exhibited abnormal aggregation and disorganization of dermal collagen in the superficial dermis, closely apposed to the epidermis but without transepidermal elimination. In contrast, biopsies of mature umbilicated plaques revealed typical collagen extrusion with overlying keratotic plugs. Sequential Masson's trichrome and elastic fiber staining further supported a stepwise evolution from superficial collagen remodeling to overt perforation. By correlating dermoscopic findings with sequential histopathological changes in the same patient, this case report provides direct evidence that ARPC progresses through a definable pre-perforating stage, in which epidermal disruption alone is insufficient to induce collagen elimination. Recognition of this early stage has important implications for timely diagnosis, appropriate biopsy selection, and avoidance of prolonged misdiagnosis.