Case Number : Case 2066 - 8 May 2018 Posted By: Uma Sundram

PEM. 

Agree with Vincenzo. It's supposed to be a controversial entity. Cannot be distinguished from epithelioid blue nevus. 

There aren't well designed features of PEM ( istiocytoid macronucleolated cells ), but this spot could fit better the silhouette, the pigmentation and the spindle cell nests of this lesion.

For me there is phenotype heterogeneity, cellular blue nevus and banal? I would favour benign

Great ddx; I think cellular blue nevus, PEM/epithelioid BN, and epithelioid melanoma all come into the differential in this case. Ultimately we decided that cellular blue nevus may be a better fit; there are areas that raise the possibility of 'ancient change' within a CBN, a pattern that mimics melanoma. Sclerotic entrapment of melanocytic nests is a pattern often seen in CBN with ancient change. The lesion was completely excised and the patient had no adverse events 5 years later.