Acquired perforating collagenosis (APC) is a rare dermatological condition characterized by the spontaneous eruption of skin-colored or erythematous papules or nodules that eventually ulcerate and exude collagenous material. The exact etiology of APC remains unclear, although various triggers, including infections, medications, autoimmune diseases, and trauma, have been implicated.

This case report presents a 63-year-old female with a history of diabetes who developed erythematous papules and plaques topped with thick, yellowish, hyperkeratotic, adherent crusts on the upper back following an insect bite. Histopathological examination confirmed the diagnosis of APC, characterized by a cup-shaped invagination in the epidermis containing degenerated collagen bundles and basophilic material. Masson-trichrome staining showed transepidermal elimination of the collagen fibers. Patient was initially prescribed tretinoin 0.1% cream to be applied 2x a day. However, patient was not able to apply prescribed medications. Interestingly, without any specific treatment, the patient’s symptoms gradually improved over 3 months and eventually resolved completely.

This case report highlights the spontaneous resolution of APC in a patient following an insect bite. While most cases of APC require medical intervention, this case demonstrates the potential for spontaneous healing in certain individuals. Further research is needed to understand the factors that influence the course of APC and to identify potential predictors of spontaneous resolution.