pustular rashes

Introduction

follicular (centred on hair follicle units):
- folliculitis
  - bacterial
  - viral
  - fungal
- acne vulgaris
- acne rosacea
non-follicular:
- superficial subcorneal pustules
  - generalised pustular psoriasis
  - AGEP drug reaction
  - IgA pemphigus
  - Sneddon Wilkinson disease
- deeper pustules
  - acneiform drug eruptions
  - palmoplantar pustulosis
  - miliaria (heat rash)
  - infections:
    - herpes zoster (shingles)
    - fungal - tinea incognito, kerion (fungal abscess), candida
    - scabies
  - neutrophilic dermatoses:
    - Sweets syndrome
    - Behcets disease
    - Bowel-Associated Dermatitis-Arthritis Syndrome (BADAS)
    - pustular type of pyoderma gangrenosum
    - pyostomatitis pyodermatitis vegetans
      - involves skin folds, oral mucosa with snail-track erosions and cobblestoning
      - often due to known or occult inflammatory bowel disease (IBD) so once diagnosed, may respond to empirical IBD Rx such as sulfasalazine, TNF-a inhibitors.
  - immunobullous conditions:
    - pemphigus vulgaris
    - bullous pemphigoid

exclude infection:
- wound swabs:
  - pierce intact pustule and swab for bacteria m/c/s, HSV, VZV viral PCR
- skin scrapings for fungal m/c/s and scabies if suspected
general workup:
- FBE, UEC, LFT, CRP, ESR
additional workup if suspicious of neutrophilic dermatoses or immunobullous condition:
- vasculitis screen
- connective tissue screen
- skin antibodies for immunobullous DDx
- pre-treatment immunosuppressive screen:
  - Hep B/C, HIV, syphilis, strongyloides serology
  - Quantiferon Gold
  - G6PD (if plan to use dapsone)
    - HLA-B*1301 if suspect risk of hypersensitivity (esp. those of Asian descent)
  - VZV and MMR antibodies
- multiple punch biopsies
  - histology (sent in formalin) - take from edge of pustule or intact pustule
  - culture (sent fresh in saline) - take from centre of lesion
  - direct immunoflourescence (sent fresh in saline) - take from around the lesion in normal skin within 1cm of pustule