see also:

• dermatology

• pustule is a pus filled lesion < 1cm diameter usually filled with neutrophils
• it may be infected or sterile

• 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