Toddler with Rash, Fever, and Malaise - Case of the Week

Educational Objective:

Discuss type IV hypersensitivity reactions.

Key Point:

Erythema multiforme (EM) minor is considered a type IV delayed, cell-mediated hypersensitivity reaction. Antihistamines such as cetirizine provide symptomatic relief of the pruritus. If triggered by a drug, the drug should be discontinued in order to prevent the development of a more severe type IV reaction such as Stevens Johnson syndrome or toxic epidermal necrolysis.

Explanation:

Contact dermatitis, erythema multiforme, Stevens-Johnson syndrome, and toxic epidermal necrolysis are all examples of Type IV delayed hypersensitivity reactions. Penicillins and sulfonamides are implicated as drug-related causes of EM. The rash of EM begins 2-3 weeks after initiation of the drug, is self-limited and resolves spontaneously in 2-3 weeks. Antihistamines provide symptomatic relief. THe drug should be discontinued in order to prevent a more severe type IV hypersensitivity reaction.

Type IV reactions are often also triggered by infections, especially herpes simplex virus and Mycoplasma pneumoniae. Acyclovir should be considered if herpes is thought to be the cause of recurrent EM.

Pearl:

It is easy to confuse the various “erythema something” rashes associated with infections. Erythema multiforme is most commonly associated with herpes simplex virus, but very infrequently with Lyme disease (only 2 other reported cases). Erythema multiforme associated with herpes is self-limited and resolves without treatment. Lyme disease is classically associated with erythema migrans (not erythema multiforme) and may progress from cutaneous manifestations to inflammatory arthritis, carditis and neurologic complications if left untreated.