epidermis looks normal. there is one or two superficial dermal perivascular eosinophil and lymphocyte

? drug rash [ no basal cell damage]

Patch stage kaposi sarcoma. Nice promontory!

Finding this difficult. There are some extravasated erythrocytes, made me consider a pigmented purpuric dermatosis, but no haemosiderin deposition! Would do levels, subtle changes in what we have here. 

Lymphocytic vasculitis, tight cuffing of blood vessels with lymphocytes, some extravasated RBCs, May be a sort of pigmented purpuric dermatosis

It's a tough case. No-one has got it right yet. It appears in the list of 'invisible dermatoses'. See https://link.springer.com/content/pdf/bbm%3A978-1-4612-5264-1%2F1.pdf

? Telangiectasia macularis eruptiva perstans. 

7 hours ago, Eman El-Nabarawy said:

? Telangiectasia macularis eruptiva perstans. 

Very difficult. But I would agree with Eman. 

After the clue of "invisible dermatoses" agree with mastocytosis (TEMP)

Thanks a lot sir for discussing this important topic

TMEP

Yes, this is a recent case of mastocytosis. But I have to give all the credit to the clinician who had suggested mastocytosis. This prompted the original pathologist to request CD117 (shown below). The case was passed to me to report in the absence of the original pathologist since the report was required urgently with the patient due back to clinic. I was quite surprised when I saw the CD117, and I am certain I would have missed the diagnosis otherwise. I can see that some of you have got the diagnosis, perhaps slightly aided my clue of 'invisible diagnosis'. Certainly it would have been invisible to me but for the CD117 already requested. Many of the mast cells are rather spindly and easily missed on the H&E. The clinician did not suggest a subtype of mastocytosis, and I would probably not attempt to subtype based on the histology. I don't think the vessels are particularly telangiectatic, and would probably favour urticaria pigmentosa (macular-papular cutaneous mastocytosis), but as I say. this aspect needs clinical correlation. Of course, such a patient also needs a work up for potential systemic involvement.

BW, Saleem

Thanks for sharing this great case.

From clinical prospective maculopapular cutaneous mastocytosis in increasing used that encompass both UP/TMEP and much easier for “lumpers”. TMEP is not a common clinical pattern of presentation and even in such cases one can still see tan brown macules and barely raised papules of UP if you look hard enough for them. 
 

Saleem, the reference you kindly provided looks like a possible book chapter in PDF rather than an article. Would you kindly be able to provide further details of that source please (if feasible)?

Hi Saman. Unfortunately I don't know the source of the list, it came up directly from Google.

Here is another article which looks useful https://www.diagnostichistopathology.co.uk/article/S1756-2317(18)30107-5/fulltext but I don't have access to the pdf. I think I will ask our hospital library to request this article. I have heard Dr Tomasini previously lecture on this subject.

BW
Saleem

Thanks very much Saleem, will source the other article too. 

I have the pdf of the article. If you want to give me your email address, I can email it to you.

Very noble of you Saleem, I sent a separate message which I hope you will be able to access in the top right corner next to the bell once you signed in.

On 07/07/2021 at 09:29, Saleem Taibjee said:

Here is another article which looks useful https://www.diagnostichistopathology.co.uk/article/S1756-2317(18)30107-5/fulltext 

Difficult case and great article Thanks!

Very interesting discussion about mastocytosis as an "invinsive dermatosis". I think there has been quite some arguments about "how much" is "too much" as for the exact numbers of mast cells count. what criteria you guys use to define it is too much and need be consider as cutanoeus mastocytosis? and then when you think it is too much, how do you define the increased mast cells are reactive like those seen in inflmmatory dermatosis, or neoplastic as in mastocytosis? love to hear your input. Saleem.

On 06/07/2021 at 12:12, Saleem Taibjee said:

Yes, this is a recent case of mastocytosis. But I have to give all the credit to the clinician who had suggested mastocytosis. This prompted the original pathologist to request CD117 (shown below). The case was passed to me to report in the absence of the original pathologist since the report was required urgently with the patient due back to clinic. I was quite surprised when I saw the CD117, and I am certain I would have missed the diagnosis otherwise. I can see that some of you have got the diagnosis, perhaps slightly aided my clue of 'invisible diagnosis'. Certainly it would have been invisible to me but for the CD117 already requested. Many of the mast cells are rather spindly and easily missed on the H&E. The clinician did not suggest a subtype of mastocytosis, and I would probably not attempt to subtype based on the histology. I don't think the vessels are particularly telangiectatic, and would probably favour urticaria pigmentosa (macular-papular cutaneous mastocytosis), but as I say. this aspect needs clinical correlation. Of course, such a patient also needs a work up for potential systemic involvement.

BW, Saleem

Hi Henry

Honest truth is that I don't have good criteria for how many mast cells are too many i.e. for when it is mastocytosis, and this is an area which also vexes me.

I don't know whether this has been systematically studied?

BW

Saleem

9 hours ago, Saleem Taibjee said:

Hi Henry

Honest truth is that I don't have good criteria for how many mast cells are too many i.e. for when it is mastocytosis, and this is an area which also vexes me.

I don't know whether this has been systematically studied?

BW

Saleem

Thank you Saleem. here are some from the Steven Billings book. but still not clear as to what about cases with  12 mast cell/HPF? 

In the following book, For TMEP, the criteria is : 

on special stains:

>=10 masts/HPF/perivacular: Dx

6-9/HPF: Suspicious

3-5/HPF: Typical Clinical Features for Dx

Then, there are papers stating this:  https://pubmed.ncbi.nlm.nih.gov/19719830/   ( All these materials are courtesy from Twitter discussions about TMEP)

It's a confusing area. I found this table from a recent paper Kirsten N et al, JEADV 2017, but noting that the numbers are /mm2 rather than /HPF. One of the authors' message is that mast cell number count can vary significantly from one section to the next in the same biopsy. There did not seem to be significant differences in staining between IHC for CD117 and tryptase. The mean values in TMEP are really quite low, very much seeming to emphasise that the mast cell numbers can be at the upper end of 'normal'. The diagnosis seems to depend very much on Clinicopathological correlation, which does feel a bit unsatisfactory from an objective aspect, and one also wonders the effect of anatomical site. This is starting to show some parallels with examples of paucicellular lentigo maligna, where again absolute numbers of cells can be unreliable.

It's a confusing area. I found this table from a recent paper Kirsten N et al, JEADV 2017, but noting that the numbers are /mm2 rather than /HPF. One of the authors' message is that mast cell number count can vary significantly from one section to the next in the same biopsy. There did not seem to be significant differences in staining between IHC for CD117 and tryptase. The mean values in TMEP are really quite low, very much seeming to emphasise that the mast cell numbers can be at the upper end of 'normal'. The diagnosis seems to depend very much on Clinicopathological correlation, which does feel a bit unsatisfactory from an objective aspect, and one also wonders the effect of anatomical site. This is starting to show some parallels with examples of paucicellular lentigo maligna, where again absolute numbers of cells can be unreliable.

Going forwards, ideally we need a marker of neoplastic vs reactive mast cells, if such will ever exist, assuming that the mast cells in mastocytosis are clonally expanded/neoplastic? I don't get the impression that histology morphology of the mast cells allows us to distinguish cutaneous mastocytosis from normal.

The paper above on p16 looks interesting. I think I might try it out!