Upadacitinib in refractory acquired reactive perforating collagenosis with atopic dermatitis and chronic kidney disease: a case report

BackgroundAcquired reactive perforating collagenosis (ARPC) is a rare perforating dermatosis characterized by transepidermal elimination of degenerated collagen fibers. It frequently develops secondary to systemic comorbidities, including diabetes mellitus, chronic kidney disease (CKD), and atopic dermatitis (AD), which limit therapeutic options and contribute to unpredictable outcomes. Here, we report a case of ARPC with concurrent AD in a patient with type 2 diabetes mellitus and stage 4 CKD, who experienced acute paradoxical exacerbation within 24 h of dupilumab initiation and achieved sustained remission with upadacitinib.Case summaryA 72-year-old male presented with a 5-year history of recurrent generalized pruritus, erythema, papules, and nodules. Despite treatment with glucocorticoids and anti-allergic medications, the skin lesions remained poorly controlled. Histopathological examination revealed transepidermal elimination of collagen fibers through the ulcer bed into the underlying dermis. Verhoeff-van Gieson staining demonstrated collagen fibers traversing the ulceration. The patient was diagnosed with ARPC. He had poorly controlled comorbidities, including AD, type 2 diabetes mellitus, and stage 4 CKD. Dupilumab was administered as a single 600 mg dose but was discontinued due to paradoxical worsening within 24 h. Following two years of recurrent relapses despite systemic corticosteroids, antihistamines, and thalidomide, oral upadacitinib 15 mg once daily was initiated, with marked resolution of skin lesions and pruritus. After 9 months of treatment, upadacitinib was discontinued, and the patient remained in stable remission at 1-year follow-up. No adverse effects were observed, and renal function remained stable throughout treatment.ConclusionThis case suggests that upadacitinib is a promising salvage therapy for refractory ARPC, particularly after failure of Th2-targeted biologics. Its favorable safety profile at the standard dose without adjustment in stage 4 CKD supports its use in patients with complex comorbidities.