What is Erythema Multiforme?
Erythema Multiforme (EM) is an acute, self-limited, and sometimes recurring skin condition considered to be a hypersensitivity reaction. It is characterized by the sudden appearance of distinctive target-like lesions. The condition is often triggered by infections, particularly
herpes simplex virus (HSV) and, less frequently, by medications or other underlying medical conditions.
Histological Features
Histologically, Erythema Multiforme presents with a variety of features that can aid in its diagnosis. The key characteristics include:-
Epidermal changes: There is often evidence of
keratinocyte necrosis and apoptosis, primarily involving the basal layer of the epidermis. This can lead to subepidermal blistering.
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Interface dermatitis: This is characterized by a band-like infiltrate of lymphocytes at the dermoepidermal junction, often accompanied by vacuolar degeneration of the basal layer.
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Infiltration of inflammatory cells: The dermis typically shows a perivascular infiltrate of mononuclear cells, including lymphocytes and histiocytes. Occasionally, neutrophils and eosinophils may also be present.
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Papillary dermal edema: Mild to moderate edema in the papillary dermis is commonly observed.
Pathogenesis
The pathogenesis of Erythema Multiforme is complex and involves both immune-mediated and direct cytopathic mechanisms. The presence of
immune complexes in the superficial microvasculature of the skin has been proposed as a contributing factor. An overreaction of the immune system to infections or drugs leads to the recruitment of cytotoxic T-cells and the release of inflammatory cytokines, which in turn cause damage to keratinocytes and the dermoepidermal junction.
Diagnosis
The diagnosis of Erythema Multiforme is primarily clinical, supported by histopathological findings. A biopsy of the lesion can help confirm the diagnosis. Key histological features such as interface dermatitis with necrotic keratinocytes and a lymphocytic infiltrate are indicative of EM. Direct immunofluorescence may reveal
deposition of immunoglobulins and complement at the dermoepidermal junction.
Differential Diagnosis
- Stevens-Johnson Syndrome (SJS) and Toxic Epidermal Necrolysis (TEN): These conditions are part of a spectrum with EM but are more severe and involve extensive epidermal detachment.
- Bullous pemphigoid: Characterized by subepidermal blisters, but with a different immunopathological profile.
- Pemphigus vulgaris: Shows intraepidermal acantholysis and a different immunofluorescence pattern.
- Fixed drug eruption: Typically presents with a localized reaction and histologically shows a dense lichenoid infiltrate.Treatment
The management of Erythema Multiforme involves addressing the underlying cause. For HSV-associated EM, antiviral therapy can be beneficial. In cases triggered by medications, discontinuation of the offending drug is crucial. Supportive care includes the use of topical corticosteroids and antihistamines to alleviate symptoms. Severe cases may require systemic corticosteroids or other immunosuppressive agents.Prognosis
The prognosis for Erythema Multiforme is generally good, especially for mild cases. Most patients experience resolution within 2-4 weeks. However, recurrences are common, particularly in those with HSV-related EM. Identifying and managing triggers can help reduce the frequency of episodes.
