Practice Essentials
Id reaction, or autoeczematization, is a generalized acute cutaneous reaction to a variety of stimuli, including infectious and inflammatory skin conditions. The pruritic rash that characterizes the id reaction, which is considered immunologic in origin, has been referred to as dermatophytid, [1] pediculid, [2] bacterid (when associated with a corresponding infectious process), and tuberculid (when associated with tuberculosis). [3] Noninfectious etiologies include stasis dermatitis, dyshidrotic eczema, medications and topical creams, tattoo ink, sutures, and radiotherapy. [4]
Clinical and histopathologic manifestations are variable and depend on the etiology of the eruption, and systemic manifestations may occur. [5, 6, 7] (See the image below.)
Id reaction (autoeczematization). Image from DermNet New Zealand (https://www.dermnetnz.org/assets/Uploads/dermatitis/a-ecz2.jpg).
Pathophysiology
While the exact cause of the id reaction is unknown, the following factors are thought to be responsible: (1) abnormal immune recognition of autologous skin antigens, (2) increased stimulation of normal T cells by altered skin constituents, [8, 9] (3) lowering of the irritation threshold, (4) dissemination of infectious antigen with a secondary response, and (5) hematogenous dissemination of cytokines from a primary site. Some cases have been related to medications and intravenous immune globulin (IVIG). [10] Id reaction has also been noted with bacille Calmette-Guérin (BCG) therapy. [11]
Etiology
The etiology of id reactions includes the following:
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Infections with dermatophytes, pulmonary histoplasmosis, [12] mycobacteria, [13] viruses, [14] bacteria, or parasites (pediculosis) [2]
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Immunization reactions - Id reactions have been reported following BCG therapy [11]
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Miscellaneous noninfectious reactions - Medications and topical creams, sutures, and radiotherapy [4]
With the growing popularity of tattoos, id reactions to red tattoo ink have been increasingly noted, as well as an id reaction reported following laser tattoo removal. [17, 18] Neosporin was found to be the trigger for an id reaction in an immunocompromised patient. [19]
No consensus has been reached on whether papulonecrotic tuberculid [20] represents a true hypersensitivity reaction rather than the result of a local cutaneous tuberculosis infection because of the identification (by polymerase chain reaction) of Mycobacterium tuberculosis in some lesions. [7, 21]
Epidemiology
The exact prevalence of id reaction is not known. Dermatophytid reactions are reported to occur in 4-5% of patients with dermatophyte infections. Id reactions have been reported in up to 37% of patients with stasis dermatitis. Furthermore, an estimated two thirds of patients with contact dermatitis superimposed on stasis dermatitis develop an id reaction.
Predilections according to age group are unknown but are influenced by the primary cause of the reaction. The condition has no known predilection for either sex. The condition has no known predilection for any racial or ethnic group.
Prognosis
Prognosis is good once the inciting etiology has been identified and appropriately treated. Morbidity results from symptoms of the id reaction and the acute onset of the primary eruption.
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Id reaction (autoeczematization). Image from DermNet New Zealand (https://www.dermnetnz.org/assets/Uploads/dermatitis/a-ecz2.jpg).
