Case Number : Case 4163 - 04 January 2023 Posted By: Iskander H. Chaudhry

Lichen planus -like keratosis aka benign lichenoid keratosis.

I'd wonder about lichenoid drug eruption given the multiple lesions, scattered eos, and patient age.

Pityriasis Lichenoides Chronica?

I favour pityriasis lichenoides chronica but some of the keratinocytes in the 3rd picture look atypical and are pushing the boundary for reactive atypia.

Same differentials lichenoid drug and pityriasis lichenoides. Extravasated RBCs also raise suspicion of lichenoid PPD, although site is odd for it. 

Difficult. ? Extragenital LSA. 

Too much parakeratosis. ? Lichen planus like keratosis (Lichenoid keratosis)

PLC certainly a DD

Why not a Grover disease?

Tricky to give a single encompassing diagnosis. Papular lichen planus would be an obvious one from clinical and there is focal wedge-shaped hypergranulosis. I'd guess PLC unlikely from clinical. One must always consider the great modern mimic of MF but it rarely is truely lichenoid with civatte and colloid bodies so the suggesion of extra-genital LS is also not bad. Drug reaction can mimic most patterns but is this a "loco-regional" issue from the limited history. Okam's razor says try to make the simplest single unifying diagnosis but this is a challenge here so we should consider dual pathology. Lichenoid keratosis would be usually solitary on upper trunk in my experience and does not have acantholysis. The acantholysis might be focal and incidental but Grover's is also common at this age. Finally we have to address the atypia and "eye-liner" sign which might be clues to a subtle bowen's. Would be good to know what Iskander called it.

I personally favour Lichen Planus over Lichenoid drug reaction. The pointers towards a Lichenoid drug reaction over and above Lichen Planus are generally deeper infiltrates, presence of apoptotic keratinocytes and Eosinophils all of which are appreciably absent in this slide. For PLC lymphocytic vascultis is usually seen which is again missing here. SO I favour Lichen Planus over and above Lichenoid drug reaction.

Thank you very much for your comments. The images show skin with a parakeratotic mounds, psoriasi-form hyperplasia, moderate spongiosis, vascular ectasia, and neutrophilic debris. There are dysmaturative foci with keratinocyte atypia. Vacuolar interface and subtle apoptosis are seen. There is no acantholysis seen. Dermal pigment incontinence is seen.

The diagnosis is Grover Disease With Epidermal Dysmaturation and Lichenoid Patterns. 

As commented on the differential diagnoses include: Pityriasis lichenoid chronica and a drug eruption. Psoriasis is less likely despite the presence of neutrophils which may be due to excoriation.