Quiz 54: What is your diagnosis?

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Diagnosis: Quiz 54

Quiz 54

Answer:  Viral exanthem

Criteria for diagnosis clinically: A widespread eruption of pink papules with a subtle violaceous cast, some of which, by virtue of confluence, have assumed configurations somewhat annular and polycyclic, is that of a viral exanthem.

Differential diagnosis clinically: This could be a drug eruption or a manifestation of lupus erythematosus, analogous to that pictured in Quiz 759. Biopsy is the arbiter of the matter.

Criteria for diagnosis histopathologically: A very sparse superficial perivascular infiltrate of lymphocytes, a few extravasated erythrocytes in the papillary dermis, a few lymphocytes scattered along the dermoepidermal junction in conjunction with a hint of vacuolar alteration, and a few lymphocytes present in the spinous zone in association with a rare necrotic keratocyte, but no spongiosis, are findings most in synchrony with a viral exanthem.

Differential diagnosis histopathologically: This could be a drug eruption of one type. Although no criteria histopathologic exist which enable that possibility to be excluded with surety, the extraordinary paucity of lymphocytes favors strongly a cause viral.

Clinicopathologic correlation: The lesions are elevated only slightly because the infiltrate of inflammatory cells is so sparse, the redness resulted from venules and capillaries dilated widely in vivo and there stuffed with red blood cells, the very slight violaceous hue is a reflection of some erythrocytes having been extravasated in the papillary dermis, and the surface is smooth because the stratum corneum is normal.

Options for therapy predicated on knowledge of histopathologic findings: If the diagnosis of viral exanthem correlates with the features clinical, then an eruption such as this one would be expected to wane in a matter of days. That is what did transpire. Moreover, the patient denied taking any drugs.

1) The presentation clinical is consonant with a manifestation of lupus erythematosus and of a drug eruption. The findings histopathologic, especially the absence of mucin from the reticular dermis, the absence of a "smudged" appearance of the dermoepidermal junction in even a single locus, and the absence of focal thinning of the epidermis militate against lupus erythematosus. On morphologic grounds alone, i.e., clinical and histopathologic, a drug eruption cannot be excluded, but, as already was mentioned, the sparseness of the infiltrate of lymphocytes is more in keeping with a viral exanthem than with a drug eruption of any kind. The possibility of a drug eruption seems to have been eliminated by the patient's claim to be taking no drugs. In short, although we favor a diagnosis of viral exanthem, the possibility of drug eruption cannot be excluded with finality solely on the basis of the evidence morphologic. 

2) This Quiz instructs, once again, that there are outer limits to what the eye (attached to a brain) is capable of concluding about changes in a particular section of tissue. In the majority of instances, a histopathologist is able to come to a diagnosis of disease of the skin with exactness. In other circumstances, such as this one (and also in that of Quiz 759), a reasonable differential diagnosis can be proposed, but some degree of uncertainty still must obtain. Acknowledgement of that lack of surety is essential to both growth intellectual and competence, ever-increasing, of a histopathologist.

3) Perhaps the greatest failure of pathologists in general and of dermatopathologists in particular is inability to recognize their own limitations and, most egregious of all, incapability of acknowledging error. All of us know fellow pathologists who, at least in their own mind, are never wrong. They are dangerous! Be good enough to call to my attention the next time you hear a kindred pathologist admit, forthright and unflinching, an error incontestable in diagnosis with these three words, "I was wrong."

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