Question 15.1

A 64-year-old man with a past history of CLL presents with fever and malaise after an 8-day illness for which he was originally prescribed celecoxib.
The photographs below are of his forehead (figure 1) and back (figure 2).


What is your differential diagnosis?

Give two investigations that would aid diagnosis.

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College Answer


  • Severe drug hypersensitivity reaction
  • Erythema multiforme 
  • Stevens Johnson/TENS
  • Viral infection 
  • Herpes simplex
  • Varicella 
  • Bacterial infection – staphylococcal scalded skin syndrome 
  • Autoimmune bullous disease
  • Urticarial vasculitis


  • Skin biopsy 
  • HSV and varicella PCR
  • Viral serology 
  • Mycoplasma serology


The college did not provide us with a picture of the patient. Given the breadth of differential diagnosis offered, it is difficult to Google a satisfactory rash picture for this question. The picture of the back is a shot of somebody with Stevens-Johnson syndrome, stolen from Medscape; the face is apparently also SJS but it is from the slightly less reputable, where it is featured as a flashcard.

Without reliable pictures from the college paper, it is difficult to generate a sensible list of counter-differentials to match the college answer.

However, at this stage the author of these notes must humbly confess that even if the rash picture was available in high resolution, he would likely still be powerless against its mysteries.

In view of this, here is a generic list of differentials one could spout, for the question "name that rash". It is so generic that it is applicable even if one cannot see the skin.

Vascular causes:

  • Shower of emboli
  • Vascular insufficiency

Infectious causes:

  • Toxic epidermal necrolysis
  • Staphylococcal scalded skin syndrome
  • Viral exanthem/manifestations of viral infection
  • Fungal infection eg. candida
  • Streptococcal toxic shock syndrome (erythroderma)

Neoplastic causes:

  • Cutaneous lymphoma/leukaemia

Drug-related causes

  • Stevens Johnson syndrome
  • Red Man syndrome (vancomycin)

Autimmune cause

  • Allergic reaction
  • Vasculitis
  • Erythema multiforme
  • Graft-versus-host disease
  • Bullous pemphigoid

Traumatic causes

  • Burns

The standard work-up:

  • FBC for eosinophilia
  • Viral serology for HSV, VZV, HIV, EBC, CMV
  • Culture of exudate
  • Mycoplasma serology
  • Vasculitic screen
  • Skin biopsy


Ely, John W., and Mary Seabury Stone. "The generalized rash: Part I. Differential diagnosis." Am Fam Physician 81.6 (2010): 726-734.

Bachot, Nicolas, and Jean-Claude Roujeau. "Differential diagnosis of severe cutaneous drug eruptions." American journal of clinical dermatology 4.8 (2003): 561-572.