Case Number : Case 2012 - 21 Feb 2018 Posted By: Iskander H. Chaudhry

Thanks for sharing clinical photographs. The epidermis shows parakeratosis with deficient granular layer, acanthosis, altered architecture of keratinocytes and a few apoptotic keratinocytes. Dermis shows edema, dilated vessels and perivascular lymphocytic infiltrate. Clinical photographs show a symmetric erythematous papulosquamous rash. This looks like a psoriasiform drug eruption.

Paraneoplastic Pityriasis Rubra Pilaris (PRP)>

Nice example of PRP, not sure labelling it as paraneoplastic just because of the background is justified. 

I agree drugs and psoriasiform/PRP-like drug or just PRP. I was not actively aware PRP could be paraneoplastic (cue a google!). I'd also add in some other "histological" differentials such as the nutritional deficiency group here (including necrolytic migratory erythema, Zinc deficiency etc). I thought there might be some neutrophils. I'd would do a PAS for fungi in routine sign-out..

One clinical point against PRP is the absence of follicular keratotic papules. Secondly, PRP's association with neoplasia could be fortuitous as Dr Saman has pointed out. It doesn't fulfill Curth's criteria.

Dr Chaudhry's Final diagnosis: PRP as it fitted with the clinical - differential was a PRP like drug eruption. Interestingly the typical alternating para and hyperkeratosis are not clearly seen - is that other people's experience ? 

An older version of Weedon says it's one of the diagnoses he missed most frequently. We rarely see it biopsied here because clinicians don't necessarily biopsy clear-cut cases or it's just uncommon, so I tend to collect them in my slide collection (just searched the database and I have 9 collected, 4 photographed, only 3 cases suggested PRP on the histo request form clinically which is interesting). In my overall experience they don't tend to read the textbook! We usually need our clinical colleagues to give us this diagnosis although I have suggested it a few times with variable clinical correlation.