Case Number : Case 2757 - 29 January 2021 Posted By: Dr. Richard Carr

I would take into consideration a pigmented epithelioid melanocytoma, mostly due to the presence of epidermal hyperplasia and prominent nucleoli.

Totally agree: PEM. It could show a PRKRA1 related cytoplasmic protein loss.  

My thought is also PEM..

I would consider what some call as BLITZ (combination of Blue nevyus+spitz nevus) or some other call such lesions as superficial DPN. PEMC also a possibility. Tough to differentiate between these lesions. 

Argee with PEM 

Agree with the favoured diagnosis of PEM. Clues here include a slightly more naevocellular junctional nest (PEM are often combined with naevocellular naevi that are BRAF positive - although this case was BRAF negative). They can be near impossible to distinguish from epithelioid variant of blue naevus but blue naevi are usually S100 weak or negative (compared with strong MelanA) and this case was S100 positive. DPN is another challenging differential but they usually show cytoplasmic & nuclear beta-catenin. We don't have PRKRA1 available but I think given the lesion is fairly typical for PEM and lacked worrying histological features I was happy to sign it out as a PEM. One should probably ensure complete removal and enquire as to the possibility of associated Carney's. Regarding BLITZ this is not a good term "blue" and "Spitz" are mutually exclusive based on driver mutations. So you can have a blue naevus-like Spitz or a Spitz-like blue neavus but BLITZ is not a thing. It should be noted that or two PEMs in one of the larger papers are re-classified as blue naevi based on their driver mutations. Also it is possible to have a blue naevus driver mutation with a PRKRA1 abnormality! i.e. a "blue PEM"

Thanks, Richard!!!