Case Number : Case 4174 - 19 January 2023 Posted By: Saleem Taibjee

There is a nice subcorneal pustule with some surrounding spongiosis. At the extreme ends of the biopsy piece, neutrophils are seen in the stratum corneum on the left side and parakeratosis on the right. I would delve into any personal or family history of psoriasis and also into any history of drug therapy. I would also enquire whether the pustules are in a circinate or serpiginous arrangement. Having said that, the differentials here consist of generalized pustular psoriasis, acute generalized exanthematous pustulosis and subcorneal pustular dermatosis/IgA pemphigus. I would do DIF to rule out IgA pemphigus. Gram staining and culture of the pustular contents will rule out any infectious cause. Generalized pustular psoriasis and AGEP are the strongest possibilities and clinico pathological correlation will settle the issue.

To me there appear to be hyphae in last panel left image. Will do a PAS to check pustular Tinea. If that is ruled out pustular psoriasis, AGEP, SCPD and IgA pemphigus are the differential diagnosis. 

The patient is a 10 year old girl, making some of the above suggestions unlikely.  I suspect that Saleem has deliberately withheld some important clinical details in this case, perhaps relating to the patient's immune status.

Of the proferred suggestions I would go for pustular psoriasis, pending further information.

what about Impetigo?

Anil has very nicely taken us through the differential diagnosis for subcorneal pustules. Beyond that, unfortunately this type of case really depends upon clinical correlation, and sometimes the clinical evolution.

It transpired that this was a paediatric example of pustular psoriasis, but as I say, this only became evident at the MDT discussion when the clinical evolution had become apparent.

BW

Saleem