Dr. Ted Rosen and Dr. April Armstrong discuss highlights from their panel discussion on Medical Dermatology Mysteries on Wednesday, November 8, 2023, at the 4th Annual Elevate-Derm PA/NP Conference in Coachella Valley, California.

In this video

Interviewed by Veronica Richardson, DCNP, both speakers describe how they approach a case when the diagnosis isn't obvious. Dr. Rosen literally writes his differential on paper so he can systematically rule entities in or out, noting this happens "more often than I think we care to admit." Dr. Armstrong sorts cases into large categories first — medication, autoimmune disease, infection, malignancy — and warns against "premature closure," the leading cause of misdiagnosis, and against anchoring bias when inheriting a patient's prior diagnosis. She documents her uncertainty in the note ("favor eczema, but differential may also include X, Y, and Z") and stresses giving patients a fresh pair of eyes.

Dr. Rosen walks through a 48-year-old man with explosive lower-extremity ulcers that proved to be severe ulcerative sarcoidosis, reminding listeners that sarcoid — like syphilis and tuberculosis — is a "great mimicker" and that once tissue is obtained it can be pushed further with special stains, immunohistochemistry, PCR, and imaging. Dr. Armstrong reviews her differential for erythroderma, from erythrodermic psoriasis, PRP, and severe eczema to drug eruptions, staph scalded skin syndrome, cutaneous T-cell lymphoma/Sézary, and rarely internal malignancy in the elderly. Both close on framing complex cases as an opportunity, being honest with patients about a long "journey together," and repeating prior tests because "diseases evolve."

  • Write your differential down on paper so you can systematically rule entities in or out — it checks you against a long list you can't hold in memory.
  • Sort tough cases into big buckets first — medication, autoimmune, infection, malignancy — then work down within each.
  • Avoid premature closure and anchoring bias; give inherited patients a fresh evaluation and document your uncertainty in the note.
  • Keep the "great mimickers" — sarcoid, syphilis, tuberculosis — in every differential; granulomas should raise sarcoid, and tissue can be pushed with special stains, IHC, PCR, and imaging.
  • For erythroderma, don't miss CTCL/Sézary and, in the elderly, internal malignancy after a negative workup.
  • Set expectations with patients that this is complex and may be a long journey — and repeat prior tests when needed, because "that was then, now is now."