Case Number : Case 4049 - 28 July 2022 Posted By: Saleem Taibjee

I'd like a spirochete stain to rule out syphilis

Secondary syphilis is a good suggestion but the duration and pruritus do not favour it. Interface dermatitis, lymphocytic exocytosis, neutrophilic parakeratotic crust and perivascular lymphocytic infiltrate are the features suggestive of pityriasis lichenoids.

agree, but Plasma cells are seen. In classic Pityriasis lichenoides plasma cell should not be there

. how to explain here 

Combined reaction pattern, lichenoid and spongiotic..Many DD needs clinical correlation indeed..Parakerstosis with neutrophils and neutrophilic subcorneal abcsess (together with itching must exclude fungal infection!).. ?Id reaction..?Lichenoid drug reaction..

Agree with ba MH-like reaction of secondary syphilis. 

Yes, well done. This is a recent case of syphilis. The mixed pattern, and additional plasma cells, are clues. Here is the Trepenema stain below.

BW, Saleem