Case Number : Case 2981 - 9 December 2021 Posted By: Saleem Taibjee

Inverted follicular keratosis with sebaceous differentiation in some areas.

agree to Inverted follicular keratosis of helwig with some amount of sebaceous differentiation

Agree with IFK admixed with sebaceoma 

Agree with seborrhoeic keratosis / IFK with sebaceous differentiation. According to a recent November 2021 article in AJDP, seborrhoeic keratosis is the preferred term unifying the entities variably labeled as superficial epithelioma with sebaceous differentiation and reticulated acanthoma with sebaceous differentiation. The same article also advocates exclusion of  Muir–Torre syndrome in such cases. 

Yes, well done. I also thought this is a great example of seborrheic keratosis/inverted follicular keratosis with sebaceous differentiation. The areas of typical seborrheic keratosis, including nice squamous eddies as shown in the images above, helps to distinguish between a primary sebaceous neoplasm (sebaceoma) in which the cells in the basal component tend to look more primitive and larger.

I’ve seen a few examples of this over the years, but this is the most striking example I’ve come across just recently. And as Meenakshi points out, it coincided rather fortuitously with the recent publication in American Journal of Dermatopathology, so I could not resist including it on Dermpath Pro.

In this particular case, the sebaceous differentiation was so prominent that I did request IHC for mismatch repair proteins. This showed no evidence of loss on MSH2, MSH6, MLH1 and PMS2.

BW, Saleem