© Angel Fernandez Flores, MD, PhD Erythema multiforme

 

 

Erythema multiforme (EM)

 

Concept

An acute, self limited disease.

Infections, drugs or neoplastic conditions can trigger the disease.

Among drugs, alopurinol is frequently involved.

 

Pathogenesis

A retarded hypersensitivity reaction.

The outcome would be apoptosis of the keratinocytes induced by cytotoxic T-cells.

 

Types

EM minor:

Acral distribution.

No mucosal involvement.

EM major:

Acral distribution.

Mucosal involvement.

Epidermal detachment involves less than 10% of total body surface area.

 

Stevens-Johnson syndrome/Toxic epidermal necrolysis:

Widespread distribution.

Mucosal involvement.

Epidermal detachment is less than 10% of total body surface area in Stevens-Johnson syndrome and 30% or more in toxic epidermal necrolysis (between 10% and 30%, it is considered as overlapping presentation).

 

Clinical presentation

Fever, malaisse, arthralgias, respiratory symptoms.

The cutaneous lesions usually appear about two weeks later.

Lesions which vary in morphology from papules to macules, vesicles, bullae or target-like lesions.

Mucosae are often involved.

 

Morphology

In early lesions, there is vacuolization of the basal layer, with lymphocytes in the dermoepidermal junction and a sparse superficial perivascular lymphoid infiltrate.

Look for individual necrotic keratinocytes in the stratum malpighii.

Another clue is the evidence of satellite cell necrosis.

 

 

When the lesion is more advanced, one can see a subepidermal bullae due to dermal edema and to necrosis of the basal layer of the epidermis.

If immunohistochemistry for Collagen IV is performed, basament membrane will be evidenced on the top of the roof.

Dyskeratosis is evidenced.

 

 

 

The stratum corneum is orthokeratotic, due to the acute nature of the disease.

 

 

 

Lymphocytes in the dermoepidermal junction, plus sparse superficial perivascular lymphoid infiltrate.

 

 

 

Necrosis of individual keratinocytes in the stratum spinosum.

Satellite cell necrosis can be seen.

 

 

Eventually, one can see well developed subepidermal bullae.

 

 

 

Immunofluorescence

Granular IgM and C3 at basament membrane and at the wall of blood vessels.

 

Main differentials

Staphylococcal scalded skin syndrome: separation of the epidermis subcorneally or within the granular layer. Such feature can be evaluated in frozen section if needed.

 

© Angel Fernandez Flores, MD, PhD