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Large plaque parapsoriasis or early patch stage mycosis fungoides? A continuous challenge.


Dr. Mona Abdel-Halim

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[center][b][i]Mona R.E. Abdel Halim[/i][/b][/center]
[center][b][i]MD, Diploma of Dermatopathology (ICDP-UEMS)[/i][/b][/center]

This area in dermatopathology has been always challenging to me. Many dermatopathologists consider large plaque parapsoriasis (LPP) equivalent to early patch stage mycosis fungoides (MF). I do believe that they are separate entities.
In Egypt, we see lots of cases presenting with light red-brown or salmon pink patches, of variable sizes, mostly larger than 5 cm, with small, scanty scales, sometimes associated with fine wrinkling, distributed mainly over the trunk, buttocks and thighs (bathing trunk) and have been there for few years. They are usually encountered in young adults. Always a clinical suspicion of patch stage mycosis fungoides is raised. However, upon pathological examination we see this mildly acanthotic spongiotic epidermis with spotty parakeratosis, superficial perivascular lymphohistiocytic infiltrate extending high up in the papillary dermis with interface lymphocytes and scattered focal single epidermotropic lymphocytes. Although the lymphocytes look cytologically normal, sometimes, it is challenging to rule out MF and there is sometimes great inter observer disagreement as regards the final signing out of these cases, some favoring to sign them out as MF, while others would prefer to sign them out as LPP.
I believe that this trend of considering LPP equivalent to patch stage MF has led to over diagnosis of MF in some centers in Egypt. Immunohistochemistry is usually not helpful as it can yield similar results and even TCR gene rearrangement studies can reveal clonal T cells in LPP. I would rather consider these cases as LPP and recommend rapid start of treatment (either topical steroids or phototherapy and follow up) rather than giving the patient a frightening diagnosis of patch stage MF and I believe that there is no need in such cases to consider any aggressive treatment. I believe that patch stage MF even in its early stages will show epidermotropism of atypical lymphocytes on a background of cold (non spongiotic epidermis) that is clear and not doubted. In other words, if it is really MF than it is MF!
In a country like Egypt, where immunohistochemistry and TCR gene rearrangement studies are expensive and diffficult to be carried out for every case, dermatopathologists should depend more on clinical and morphological criteria. I believe that scattered focal single cell epidermotropism of small lymphocytes on an inflammatory back ground favors LPP. Although there is a 10-30% incidence of LPP to progress to overt MF, LPP may persist as such for years and decades and thus treatment and follow up is important but there is no need to frighten the patient with a diagnosis of a cutaneous lymphoma.
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Dr. Phillip McKee

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Hi Mona, a very interesting blog which will be sure to cause controversy. I have always hated the term parapsoriasis because it has many variants all of which are different conditions! I am afriad that I am one of those dermatopathologists who regard large plaque parapsoriasis as synonymous with mycosis fungoides. I cannot see how one could make a pathological distinction since the features are basically the same. Spongiosis is sometimes a feature of mycosis fungoides anyway. The one thing in your blog that does raise doubts in my mind is the fact that you see these patients commonly and yet mycosis fungoides is a very rare condition. I think that you will have to embark upon a long term and complex research project to unravel this issue.
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I would agree with Prof. McKee here. Yes Large plaque psoriasis is a distinct entity but it should for practical purposes be considered as a precursor/ early form of MF, with a very good prognosis.

However you are right. The patients should not be told that this is MF, but should be told that this is a condition that has a significant overlap with MF, which in the majority runs a benign course. I would still advise long term follow-up and for practical purposes treat like early patch stage MF.

I think the analogy its akin to MELTUMP i,e, this is an atypical inflammatory rash of uncertain significance (I dare not suggest a new acronym AIRUS)

:)
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