Case Number : Case 2314 - 30 April 2019 Posted By: Uma Sundram

Subepidermal split with mononuclear cells and eosinophils  along with the age of the patient are the features that are suggestive of pemphigoid

IgA Pemphigus, Intraepidermal Neutrophilic Variant

Im not sure of the level of the blister, for me it seems more intraepidermal than subepidermal, i dont know what is trying of show in image 3 but i think that is something important.

My differential would be IgA Pemphigus and i cant rule out a frictional etiology.

I see an erythema multiforme-like pattern and a large bulls pemphigoid-like blister, without eosinophils...why not a paraneoplastic pemphigus?

sub epidermal bulla with necrotic keratinocytes and bulla space continue necrotic large cells

? drug rash

Great differential. Yes, the keratinocytes high in the epidermis is supposed to make people think of a drug rash. This is an older blister with some re epithelialization; the difficulty in understanding where the split is, contributes a little to the confusion regarding the differential. I like that the ddx offered includes many different primary autoimmune blistering diseases, which would be difficult to rule out without DIF. The DIF is negative. The patient is on Keytruda (anti PD1) and developed this rash. It's important to think drug when you see a blister and necrotic keratinocytes, especially in the stratum spinosum.

BTW, in panel 4, you see a lot of intra-blister necrotic debris, which looks like dying cells. This should also lead one to favor a drug eruption, as it would be an unusual finding in a true primary auto immune blistering disease. That said, when the clinician biopsies an older blister, all bets are off (as they say around here).

Good learning case. Thanks Uma.