Management of common scabies and postscabetic itch in adults: Lessons learned from a single-center retrospective cohort study

Background: Common scabies can be difficult to diagnose and treat. There are limited data on the clinical characteristics of patients who may benefit from combined topical permethrin plus oral ivermectin. Postscabetic itch is common, but there is scant data describing its prognosis and management.

Objective: This study describes the clinical characteristics and evaluates treatment outcomes of participants with common scabies treated with combined topical permethrin plus oral ivermectin and describes the prognosis and management of postscabetic itch.

Methods: We conducted a single-center retrospective cohort study of participants with common scabies treated with combined topical permethrin plus oral ivermectin therapy and topical permethrin only. Participants previously treated with permethrin and/or ivermectin were excluded. The primary outcome was clinical outcome at follow-up, categorized as cure, worsening, or no change. Secondary outcomes included time from treatment initiation to cure, duration of follow-up after cure, recurrence rate, frequency of postscabetic itch, and duration of postscabetic itch.

Results: Of 55 participants treated with combined topical permethrin plus oral ivermectin, 49 (89%) achieved cure, 5 (9%) had no change, and 1 (2%) had worsening disease. Of 48 participants treated with topical permethrin only, 46 (96%) achieved cure, 2 (4%) had no change, and 0 (0%) had worsening disease. Thirty-five participants (34%) experienced postscabetic itch for 52.5 days (interquartile range, 28-135). More participants in the older (mean: 55 years; standard deviation: 21 years; p = .002) combined treatment group experienced postscabetic itch than in the younger (mean: 42 years; standard deviation: 19 years) permethrin-only treatment group (42% vs. 25%; p = .072).

Conclusion: These findings support the use of combined topical permethrin plus oral ivermectin therapy in treating common scabies, highlight that postscabetic itch can persist for longer than previously reported, and reveal a potential relationship between older age and postscabetic itch.