Differential Diagnosis

Common Diagnoses

Occasional Diagnoses

Rare Diagnoses

  • Dermatitis Herpetiformis
  • Behçet’s Syndrome
  • Viral: Cowpox and Orf (Note: Chickenpox is Vesicular, Not Pustular)
  • Hot Tub Folliculitis (Superficial Pseudomonas Infection)
  • Drug Induced

Ready Reckoner

Key distinguishing features of the most common diagnoses

ImpetigoOther Staphylococcal InfectionsHerpes Simplex or ZosterAcne VulgarisRosacea
Grouped or SinglePossiblePossibleYesNoNo
Affects EyeNoNoPossibleNoPossible
Tingling before LesionNoNoYesNoNo

Possible Investigations

  • There are very few investigations likely to prove useful or necessary in primary care. The presence of widespread or recurrent candidal or staphylococcal lesions might necessitate a urinalysis or blood sugar/HbA1c to exclude diabetes; a swab of pus may help confirm a clinically suspected infective agent; and in very obscure cases, a skin biopsy might prove helpful.

Top Tips

  • Take time to explain to the patient the nature of the problem in recurrent staphylococcal infections. Exclude diabetes, check carrier sites and reassure that the patient’s ‘hygiene’ is not in question. A prolonged course of antibiotics may be helpful.
  • Check self-treatment in rosacea and perioral dermatitis. Treatment with OTC topical steroids will exacerbate the problem. Warn the patient that the condition may worsen before it improves on withdrawal of this inappropriate treatment.
  • Papules and pustules around the mouth and eyes, often with a halo of pallor around the lip margin, are caused by perioral dermatitis. Treat with antibiotics, not topical steroids.

Red Flags

  • Widespread, severe and recurrent staphylococcal lesions suggest diabetes or possible immunosuppression.
  • Localised pustular psoriasis can be very resistant to standard treatments, so have a low threshold for referral. The very rare generalised form can make the patient dangerously ill – admit urgently
  • Remember that herpes simplex or zoster infections in the immunocompromised can become disseminated and severe.
  • Ocular problems in rosacea can be complicated and troublesome – refer to an ophthalmologist.
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