[Severe immediate hypersensitivity reaction with generalized contact urticaria after cutaneous application of topical permethrin]

Background: Permethrin is a synthetic pyrethroid used as a chemical insecticide that obtained an MA in the management of human scabies in 2014. We report a case of severe immediate hypersensitivity (IH) reaction with generalized contact urticaria secondary to the cutaneous application of 5% permethrin cream (Topiscab®).

Observation: A 44-year-old woman with no personal history of atopy was treated with oral ivermectin, Topiscab® and levocetirizine for suspected scabies. Eight hours after taking a levocetirizine tablet and five hours after the application of a tube of Topiscab® together with oral ivermectin, she presented generalized urticaria, nausea and diarrhoea, followed by loss of consciousness. Skin prick-tests for ivermectin and levocetirizine were negative. We noticed non-significant erythema with permethrin. The open application test with Topiscab® was strongly positive at 20min with the appearance of an urticaria plaque in the area of application. The open test with sorbic acid was positive at 2h. Accidental exposure to permethrin spray caused dyspnoea and recurrence of urticaria.

Discussion: Mild and transient symptoms are regularly described after cutaneous application (burning, paraesthesia or increased itching). Delayed hypersensitivity reactions such as contact dermatitis have been reported in the literature. Exceptional cases of severe IH reactions have been described following occupational exposure to airborne pyrethroid insecticides. No cases of severe IH reaction secondary to application of topical permethrin have been reported.