Case Number : Case 1980 - 05 Jan 2018 Posted By: Dr. Richard Carr

Any mucin stains? Collagen is fenestrated, some fibroblasts (stellate forms) so I am thinking pretibial myxedema (clinically fits) but can not explain the associated lymphocytic infiltrate and eosinophils?? May be secondary to itching??

What about a Teleangiectasia Macularis Eruptiva Perstans?  I see some angiectatic vessels and there are some mastocytes ( aren't it?) But I find this case difficult ( and interesting ).

Agree with Vincenzo as it correlates well with clinical description

How about bug bites?

Favour TEMP but the differential is large would add spontaneous urticaria to the differential (although clinical findings are not typical)

Going back to first principles, given the eosinophils and itchy lesions noted clinically, I guess I would still favor something like bug bites or contact dermatitis (with lesions being so localized). The eosinophils seem deep for contact.

Okay I think this is one of the most common cases we see in our "non-cancer" MDMs. For years I have been seeing them and cannot label them. Basically it presents as very itchy lesions (usually erythematous macular/papular that may be excoriated or become lichenified - mild lichenification shown histologically in this case) without any obvious inciting cause. Histologically there are minimal epidermal changes, which would be odd for an arthropod reaction or contact reaction (a clue - the absence of spongiosis, like the dog that did not bark in the night - Sherlock Holmes reference) but with variable superficial perivascular lymphocytic infiltrate (generally lacks deeper component compared with arthropod reactions). Eosinophils vary from sparse to moderately numerous perivascular and scattered interstitial cells - look carefully at the sections. You may see slight "oedema" in the upper dermis.

I am now labelling this "pattern" under the rubric of "dermal hypersensitivity reaction" (AKA urticarial dermatitis, possibly AKA itchy red bump disease, possible AKA papular urticaria). I urge you to read the passage in Weedon on this. Weedon cites Steven Kossard and also others but admits to becoming a convert. But to quote from Weedon:

The author is also aware of the disdain held for converts by some persons: ‘the impudence of a bawd is as nothing to that of a convert’ – George Saville, Lord Halifax (1633–1695).

Basically we tell the clinician to look for possible causes of the pattern that might include arthropod & drugs and at least there may be a rational for treatment. I indicate to them it's a pattern (like leucocytoclastic vasculitis) not specific diagnosis as such.

This patient appears to have responded to potent topical steroid and has not come back so perhaps it was self-limiting.

I think having this pattern in your armamentarium will help you no end in these cases that are really quite common and sadly for patients often rather intractable - in some cases they seem to go from one dermatologist to the next seeking a diagnosis and more importantly relief from their symptoms and they have my sympathy as I refer to eosinophils as the nuclear weapons of the immune system - perhaps an over-statement!

Great case and discussion, Richard! I have struggled with this pattern too for many years and do use the term 'dermal hypersensitivity reaction' sometimes, although clinicians seem more comfortable with papular urticaria.