Case Number : Case 2611 - 09 July 2020 Posted By: Saleem Taibjee

There is not much change in the stratum corneum for asteatotic eczema and eosinophils are not a feature of that disorder.  The inflammation isn't showing much interest in the papillary dermis or basal layer for pre-bullous pemphigoid.  I favour scabies and would do some deeper levels.  A drug reaction is also possible of course.

The most enigmatic group of tissue reactions in inflammatory dermatopathology, Dermal Hypersensitivity Reactions (DHR). As a Clinician I approach it as a PATTERN of inflammation with a wide range of the clinical appearance of the eruption and a plethora of terminology over years. Below is a few to name:

When urticated plaques mixed/alternates with eczematous patches especially in elderly, a pre-blistering stage of BP is often suspected. Once DIF/ELISA for BP180/230 excludes this then some will be labelled as urticarial dermatitis or urticated eczema.

Intensely pruritic discrete erythematous papules scattered randomly on trunk and limbs is another not uncommon clinical presentation and these will be named Itchy Red Bumps Disease or papular dermatitis or urticarial papulosis or even some include papular urticaria among this papular presentation. (though the latter is different clinically with some differences histologically in certain cases while others may overlap histologically).

“bite, bugs and drugs”, some cases of malignancy as a paraneoplasia and even polymorphic eruption of pregnancy are reported to induce DHR patterns.

Lastly, in a large proportion of cases no convincing trigger can be found despite of extensive investigations, one then need to focus on management which is not easy and some patients ends up seeking more than one opinion to relief their disabling itch which impairs their sleep at night/quality of life.

Hope Dermpathpro team does not mind my slightly lengthy comment of this subject with a focus on some clinical aspects and re-enforcing it is not a single diagnosis and it must be correlated to the clinical presentation rather than trying to make a diagnosis on histology alone.

PAS? Silver methenamine?

elderly person with dermal perivascular eosinophils with mild irregular acanthuses and spongiosis

is there any peripheral eosinophilia in the blood counts

is he on any medications 

can we get a DIF done

Given the clinical differential between scabies, eczema and BP, I favor scabies. There aren’t any junctional eosinophils for BP, and no spongiosis and too eosinophils for eczema..Difficult, because I don’t see true pink pigtails. 

Unless the patient has "Norwegian" scabies (not uncommon in this age group) the thigh is an unlikely place to actually find the acarus.  However, the suggested clinical diagnosis of asteatotic eczema might suggest Norwegian scabies, as they are not dissimilar in appearance clinically.

Great responses! I particularly like the discussion about the location / distribution of the eosinophils in helping to discriminate between the differential diagnoses.

Quod erat demonstrandum....

Additional level below. This is the first and only case I have had in my career in which scabetic mites were not evident in the initial section, but then revealed in the levels. It was actually a case from a few years ago in which I was asked for a second opinion by a general pathologist in the department. I advised the colleague to request more levels. Presumably my colleague had then assumed that finding scabetic mites on histology is not so uncommon, and he issued a supplementary report without feeding back to me. I only became aware that the levels had confirmed scabies when the dermatologist looking after the patient mentioned the case in passing a few day later! 

Saleem - what were your final thoughts on case 2606?

Hi Richard

Sorry for the delay on case 2606.

That case is Clear Cell sarcoma.

As Vincenzo pointed out, the prominent fibrous septae are a good clue, as well prominent nucleoli. I could not identify wreath like giant cells (an additional clue) despite careful scrutiny.

As you probably all know, immunohistochemistry isn't so helpful in such cases, because clear cell sarcoma is often positive for melanocytic markers.

EWSR1 rearrangement was confirmed, supporting the diagnosis.