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multiforme erythema

Monday 21 February 2005

WKP PO

Definition : Erythema multiforme (EM) is a skin condition of unknown cause; it is a type of erythema possibly mediated by deposition of immune complexes (mostly IgM-bound complexes) in the superficial microvasculature of the skin and oral mucous membrane that usually follows an infection or drug exposure. It is an uncommon disorder, with peak incidence in the second and third decades of life. The disorder has various forms or presentations, which its name reflects (multiforme, "multiform", from multi- + formis). Target lesions are a typical manifestation. Two types, one mild to moderate and one severe, are recognized (erythema multiforme minor and erythema multiforme major).

Microscopy

- subepidermal bullae

- dermal inflammatory infiltrate (includes lymphocytes, histiocytes)

  • Eosinophils may be present.
  • neutrophils are sparse or absent.

- Overlying epidermis :

- May also have dermoepidermal bullae with basal lamina at floor of bullae
- Variable epidermal spongiosis and eosinophils
- No leukocytoclasis, no microabscesses, no festooning of dermal papillae

- Erythema multiforme may have variable histologic changes from toxic epidermal necrolysis to dermal disturbances.

Differential diagnosis

- acute graft versus host disease / acute cutaneous VHD

- fixed drug reaction

  • eosinophils
  • marked vascular wall thickening

- Steven-Johnson syndrome or toxic epidermal necrolysis

  • full thickness epidermal necrosis with separation of epidermis from dermis
  • necrotic keratinocytes at edge of bullae

- subacute cutaneous lupus erythematosus

  • fibrinoid necrosis at dermoepidermal junction with liquefactive degeneration and atrophy of epidermis / epidermal atrophy

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