Erythema Multiforme

Question 1

Define erythema multiform

Answer 1

Acute self-limiting hypersensitivity reaction of skin and mucous membranes

• EM minor – target or raised oedematous papules without mucosal involvement
involving <10% total body surface area
• EM major – target or raised oedematous papules with mucosal involvement
involving <10% total body surface area

Question 2

What are the causes/risk factors of erythema multiform?

Answer 2

Degeneration of basal epidermal cells -> development of vesicles between cells and BM
Lymphocytic infiltrate around blood vessels
Immune complex deposition
• Drugs e.g. sulphonamides, penicillin, phenytoin
• Infection e.g. HSV, EBV, Mycoplasma pneumoniae, Chlamydia, histoplasmosis
• Inflammation e.g. RA, SLE, sarcoidosis, UC
• Malignancy e.g. lymphoma, leukaemia, myeloma
• Radiotherapy

Question 3

What are the symptoms of erythema multiform?

Answer 3

• Prodrome URT illness

* Sudden appearance of itching/burning/painful skin lesions

Question 4

What are the signs of erythema multiform?

Answer 4

• Targetoid lesions
• Erythema
• Vesicles/bullae
• Urticaria
• Symmetrical
• Affects arms and legs

Question 5

What investigations are carried out for erythema multiform?

Answer 5

Usually unnecessary; erythema multiforme is very much a clinical diagnosis. Investigations may be carried out to identify the cause of EM.
• FBC - high WC, eosinophils, ESR/CRP
• U&Es - may show evidence of volume depletion/ dehydration due to infection.
• HSV Serology - positive if HSV is the underlying cause.
• Antibody Serology - ant-desmoplakin antibody may be the immunological aetiology of EM.
• PCR - to detect infectious agent.
• Mycoplasma Titres - to detect mycoplasma pneumonia.
• CXR - may show consolidation secondary to pneumonia or granulomatous lungs in sarcoidosis.
• Skin Biopsy - if the diagnosis of EM is in doubt.