Case Number : Case 2487 - 16 January 2020 Posted By: Saleem Taibjee

There is a vague dermal elastosis.Elastic fibers  disorders (mid-dermal elastolysis,anetoderma,  ...etc) need to be excluded.

But this looks cutaneous mastocytosis.

Some vascular spaces in fig 2 and 3 look like a promontory sign...Favor Kaposi's sarcoma, patch stage.

Patch stage Kaposi's sarcoma.

Argee with SK.

sir, patch stage of KS is difficult histology diagnosis. I need IHC 

also the clinical description tells papules, 

However, there are perivascular lymphocytes and plasma cells and slit like vascular spaces. some actinic damage is seen in the dermis.

There's perivascular and interstitial mononuclear cell infiltrate with some mucin. There is also an incidental pseudolipomatosis cutis.। think that this is papular type of granuloma annulare presenting as multiple papules and histologically as interstitial type. 

Tricky. Blind H&E both mastocytosis & KS went through my head too. Not sure it's either to be honest. Are there colloid bodies? May be do some levels to find the "papule". 

There is an occasional eosinophils and probably mast cells. Need stains for mast cells. Could be cutaneous mastocytosis- TMEP. Otherwise some dermal hypersensitivity reaction although eosinophils are occasional.

Well done guys! Yes, this was a pretty subtle (not quite 'invisible') example of mastocytosis. Fortunately for me, the clinician had suggested the diagnosis. The case was passed to me by another pathologist who wasn't too sure. However, once aware of the clinical suspicion I was pretty confident. I did request a CD117 (see below) for confirmation, which shows there are many more mast cells than one first appreciates. The difficulty of the case is that many of the mast cells are rather spindled which I think is the pitfall, and when it can be missed. As Meenakshi mentions, occasional eosinophils can be a clue.

I tend not to try to subtype mastocytosis on the histology, because this aspect really depends on clinical correlation. Furthermore, the classification of mastocytosis seems to be constantly changing! See https://www.ncbi.nlm.nih.gov/pmc/articles/PMC5356454/?report=reader

I don't have clinical photos on the current case since it is a backlog case from another hospital. However, I include a couple of clinical photos on one of my own patients with confirmed mastocytosis. I suspect the current case might look somewhat similar.

Guys mastocytosis went through my mind too. Thanks God hhh . Thank you so much Saleem Taibjee for such a lovely case indeed