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Probability diagnosis

Herpes simplex

Herpes zoster

Varicella (chicken pox)

Hand, foot and mouth disease

Dermatitis: contact, atopic

Insect and arachnoid bites

Molluscum contagiosum


Serious disorders not to be missed


  • Allergic vasculitis


  • Bullous impetigo (scalded skin syndrome)

  • Scabies

  • Anthrax


  • Associated e.g. lymphoma, leukaemia


  • Erythema multiforme

Pitfalls (often missed)



Dermatitis herpetiformis

Fixed drug eruption e.g. sulphonamides

Trauma e.g. skin friction, thermal, acid, caustic


  • Porphyria cutanea tarda

  • Epidermolysis bullosa acquisita

Masquerades checklist

Drugs e.g. penicillamine, barbiturates

Key history

Ask about recent and general health esp. any infections and associated symptoms of infectious diseases. Check for any recent travel history or history of skin trauma, bites or stings, as well as drug intake esp. antibiotics. Is there a family history of bullous disorders?

Key examination

General examination of skin and mucus membranes including mouth looking for hand, foot and mouth infection and pompholyx.

Key investigations

Unlikely to be helpful.


  • FBE

  • wound swabs (if evidence infection)

  • viral studies and patch testing

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