Erythema Multiforme



Background

  • Acute IV [cell mediated] hypersensitivity rxn
  • 10/7 post drug/bug/other trigger
  • Varies from mild rash to life threatening SJS-TEN
  • Precipitating factors include HSV, EBV, medications
  • May recur with repeated trigger (e.g. recurrent HSV)
  • M>F
  • Occasionally post vaccine (BCG, polio, Tdap)
  • N.B. ±mucous membrane involvement

Triggers

Almost anything but common are:

Viral:

  • HSV, CMV, EBV, Hep (all), VZV

Bacterial

  • Strep, Mycoplasma P

Drugs

  • Sulfa/penicillin based
  • Anticonvulsants

Clinical

Symptoms

  • Prodromal "URTI" → (day 3+) non-itchy rash
  • Peripheral (incl. palms/soles) ache/rash spreads centrally
  • ± mucous memb. (eyes, mouth, genital)
  • Heal (no scar, possible ↑/↓ pigmentation) after 7 days

Signs

  • ±SIRS (beware SJS-TEN)
  • Papules → tender target lesions
  • Dull-red macule, central vesicle/bulla
  • Target lesions (enflamed edges)
  • Nikolsky's negative (rub ≠ shear upper dermal layers)
target lesions

Differential Dx

  • Septicaemia (incl. meningococcal/nec. fasc.)
  • Herpes simplex virus (HSV)
  • Mycoplasma pneumoniae (±CXR)
  • Burns (chemical etc
  • Pemphigoid (beware elderly)
  • Vasculitis (tender infarcted "bruises") e.g SLE
  • Erythroderma (usually very unwell)
  • Viral exanthems (commonest in children)

Investigations

Only if clinically indicated:

  • Clinical Dx so only Ix if clinically unwell (? SJS-TEN)
  • ± CXR (pneumonia)

Management

  • Stop trigger if possible
  • Analgesia, explanation
  • Antihistamines
  • ±mouth wash
  • Consider po antivirals in (well) HSV


Content by Dr Íomhar O' Sullivan. Last review Dr ÍOS 11/04/23.