Histopathologic features of inverse psoriasis

Background Inverse psoriasis represents a less commonly described form of psoriasis in intertriginous areas. The pathologic findings of inverse psoriasis are typically grouped in with those of plaque psoriasis, as the histopathologic features specific to inverse psoriasis have not received significant investigation. Methods A single institution, retrospective cohort study was performed to review biopsy slides for psoriasis occurring in typical intertriginous areas. Patient's charts were reviewed and only those where the clinical diagnosis of inverse psoriasis was also favored were included. Results Twelve patients met inclusion criteria: 58% male and 42% female, 18 to 86 years of age. Classic features of psoriasis such as hypogranulosis, confluent parakeratosis, and thinning of the suprapapillary plate were seen in 100%. Regular psoriasiform acanthosis and dilated tortuous dermal vessels were seen in 92%. Neutrophils were present in the scale in 83% and in the dermis in 100%. Features considered atypical for psoriasis included spongiosis in 83%, eosinophils in 67%, and focal serum in the scale in 42%. Conclusions While inverse psoriasis commonly exhibits features considered to be classic for psoriasis, it is not unusual for inverse psoriasis to show features considered atypical for plaque psoriasis such as dermal eosinophils, epidermal spongiosis, and focal serum in the scale.