Case Number : Case 2827- 7 May 2021 Posted By: Dr. Richard Carr

Superficial and deep relatively well circumscribed dermal infiltrate of neutrophil polmorphs, associated with more immature appearing cells. I can see any obvious vasculitic component but is difficult to see vessels clearly. I would consider histiocytoid Sweet's syndrome. Also need to correlate with microbiology to exclude infective process, although long history since surgery. The features are not typical of a chronic peri-prosthetic reaction. 

I agree that the histology is suggestive of Sweet's syndrome.  However, the localised and persistent nature of the lesion is odd for that diagnosis and I too would be wondering about an infective process.

leuko cytoclastic vasculitis histology with somewhat  ? pseudo-cryptococcal artefact, can we have a PAS stain

Intravascular histiocytosis

Infection requires exclusion first through appropriate stains and tissue cultures. If sterile nature of the infiltrate is established, the histiocytoid/cryptococcoid neutrophilic diseases is in the DDx and requires clinical correlation. Agree with Richard such localisation will be unusual clinically. 

The list of ....oid is getting bigger. 
 

It will be interesting to see the results of other premature granulocytic markers especially MPO (if performed) and any background haematological malignancy. 

?CML

Thanks for all the great discussion comments and suggestions. I'd like to have shared the clinicals but it's becoming difficult to do. The clinical distribution was very confined around the hip and buttock - large red blotches (so let's shelve CML and infection on that basis). Her prosthesis was ceramic and not metal. I neglected to say she has a 20 year history of polymyalgia rheumatica and had a raised CRP and PV. She initially was treated with dermovate but also was developing joint pain, intermittent chest cramps and lethargy. Her oral prednisolone was increased to 15mm OD and the skin eruption resolved completely. I favoured a diagnosis of Sweet's-like (Sweet-oid!) intravascular histiocytosis related to her PMR and previous joint replacement. I did not do any "bug" stains actually as I thought it was an "immunological" reaction. I guess this is a slightly unique case but I think you all did well.