Id reactions are seen in response to a variety of disorders, including fungal infections (tinea capitis and tinea pedis), scabies infestation, pediculosis capitus, molluscum contagiosum, bacterial and mycobacterial infections, and arthropod bites. The rash appears days to weeks after the instigating rash and consists of erythematous papules (sometimes crusted at the apices) as well as eczematous patches and plaques. The rash can be local to the instigating lesions/rash, distant, or generalized. The id reaction usually presents on the extremities, commonly on the sides of fingers, but may occur on the face and trunk. Pruritus is intense. The id reaction will not demonstrate infectious organisms and may not respond to topical steroids.
Management and Disposition
Recognition and treatment of the initial infection or infestation is curative. Refer to a dermatologist for follow-up to confirm diagnosis and resolution.
Repeated ED evaluation for fungal infection or eczematous rash should prompt further investigation for a distant, untreated, or occult fungal infection.
Id reactions are intensely pruritic; make sure secondary bacterial infections do not develop from excoriations.
Recurrences are common, especially if the primary source is not treated or treated adequately.
Id Reaction. Bullous tinea pedis causing id reaction on the fingers. (Used with permission from Wolff K, Johnson RA, Suurmond D. Fitzpatrick’s Color Atlas & Synopsis of Clinical Dermatology. 5th ed. New York, NY: McGraw Hill; 2005: 48.)
Id Reaction. Reaction to tinea pedis. Erythematous, partially dried up, pruritic vesicles on the foot. (Used with permission from Goldsmith LA, Katz SI, Gilchrest BA, Paller AS, Leffell DJ, Wolff K. Fitzpatrick’s Dermatology in General Medicine. 8th ed. New York, NY: McGraw Hill; 2012: Fig. 16-7.)