Why You Might Miss This Case of Pyoderma Gangrenosum
I used to write single-dose fosfomycin prescriptions all the time, but a new Lancet trial showed me convenience is a liar. Paul and I break down why it came in last place and what we're prescribing instead, watch here.
-Simon
The diagnostic score with the highest reported sensitivity for pyoderma gangrenosum, and why colour still trips it up.
Picture the classic teaching photo of pyoderma gangrenosum: an angry red-violet border ringing a punched-out ulcer. Now picture a patient whose skin never turns that colour. A case report in the July 2026 issue of CMAJ tracks a 26-year-old South Asian woman whose ulcer edges stayed grey-brown, not red, while clinicians treated her for folliculitis and then cellulitis for weeks. What should you look for instead?
In patients with Fitzpatrick IV to VI skin, that classic redness often never shows up. Look instead for hyperpigmented, dusky, grey, or even black discolouration at the ulcer's edges. The case adds a second clue: the patient's lesions worsened every time her skin was disturbed, first from a cat scratch, then from surgical debridement, a reaction called pathergy. Pathergy plus atypical colour plus a wound that shrugs off antibiotics should move pyoderma gangrenosum up your differential. Confirm with biopsy.
In the case report, the authors used three validated scoring tools, including the PARACELSUS score, which reportedly has the highest sensitivity of the three. They compared the patient's clinical picture, biopsy, and disease course against each tool's criteria for progressive disease, pathergy, and border appearance. They found she satisfied nearly every PARACELSUS category, missing only the point tied to an associated systemic disease, since her colonoscopy ruled out inflammatory bowel disease.
If you take one thing from this post: a low PARACELSUS score in a patient with darker skin might just reflect skin tone, not milder disease. Once biopsy and culture confirm pyoderma gangrenosum, management leans on:
- Corticosteroids (e.g. prednisone, dexamethasone) or steroid-sparing cyclosporine
- Topical tacrolimus or clobetasol under wound-care guidance
- Screening for an associated systemic disease, especially inflammatory bowel disease
- Early dermatology referral, with surgical debridement avoided
Even with the right treatment, darker skin can show more visible cribriform scarring and pigment change, so it's worth discussing scar-directed therapy once the ulcer settles. On a SOO you could refer to these, and if your examiner asks "what kinds of scar-directed therapy?" you could mention:
- daily UV protection (e.g. sunscreen)
- Silicone Gel or Sheeting
- Intralesional Corticosteroids
- Referral for laser treatment
Exam tip:
If a SAMP (Select-Answer Management Problem) describes an expanding leg ulcer that has failed two courses of antibiotics, do not let the absence of redness talk you out of pyoderma gangrenosum, especially if the patient's skin tone is described as darker or the vignette mentions recent minor trauma. Pathergy and treatment failure are your distractor-proof clues, so you don't miss this.
What do attendees say about The Review Course?
"Good way to guide further studying, gives lots to build on on your own, good clinical pearls."
The Review Course 2024 Attendee
Register here!
References
Pyoderma gangrenosum in a 26-year-old woman. CMAJ. 2026. https://www.cmaj.ca/content/198/27/E1065
Comments