Spreading disease with the greatest of ease
SEEING this red scaly rash with a spreading scaly edge, you might consider sending skin scrapings for microscopy and culture to look for tinea fungus.
When both culture and microscopy come back negative, it may be tempting to prescribe a topical or oral antifungal.
However, this would not respond, as this is the most extensive SCC in situ I have ever seen, involving virtually the whole of this lady’s lower leg.
A clue to the cause is that she is immunosuppressed, taking methotrexate for rheumatoid arthritis. PDT, Efudix and Aldara have all been tried, so far without success.