Quiz 8: What is your diagnosis?

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Diagnosis: Quiz 8

Quiz 8

Answer:  Insect "bite"

Criteria for diagnosis clinically: Acuminate red papules, some solitary and others arranged in a cluster, are typical of those of insect "bites."

Differential diagnosis clinically: Lesions like these may be seen in scabies.

Criteria for diagnosis histopathologically: A "top heavy," somewhat wedge-shaped, superficial and deep, perivascular and interstitial infiltrate made up of lymphocytes overwhelmingly, but also of a few eosinophils along with some erythrocytes extravasated in the upper part of the dermis, the papillae of which are edematous, is that of a response to an insect "bite."

Differential diagnosis histopathologically: There is none except for lesions induced by arthropods other than insects.

Clinicopathologic correlation: The papule was brought into being by virtue of the infiltrate of inflammatory cells coupled with edema of the papillary dermis; the redness of it derives from venules in the upper part of the reticular dermis, in vivo,  having been dilated widely and filled with erythrocytes; and the surface is smooth because the stratum corneum is normal for epidermis in the vicinity of an elbow. 

Options for therapy predicated on knowledge of histopathologic findings: Once a diagnosis of insect "bite" has been rendered histopathologically, a clinician knows that it is merely a question of time before the lesions wane and disappear. If a patient is uncomfortable sufficiently, a fluorinated corticosteroid can be applied topically, it functioning as an "anti-inflammatory" agent by banishing lymphocytes and constricting small blood vessels.

1) The word "bite" is placed in quotation marks because an insect, such as a mosquito, does not have mouth parts analogous to those of a tick, that latter creature actually taking a nip of human skin.

2) The features clinical are stereotypical of a reaction to the "bite" of an insect. Such a fully formed lesion may be a red papule or a papulovesicle, and, episodically, even a vesicle devoid of a papular component. The infiltrate of an insect "bite" in a lesion developed fully tends to be wedge-shaped and made up of lymphocytes and eosinophils, those findings being present here, but the number of eosinophils in this instance is rather few. Of course, there are numerous variations on the themes clinical and histopathologic. For example, lesions may be bullous and be composed nearly entirely of lymphocytes.

3) The cornified layer of the lesion shown here is thicker and more compact than is expected for glabrous skin, the reason being that the one biopsied was situated on an elbow, a site that in the normal course of events is rubbed for long over many years. In short, the changes pictured in the stratum corneum of this lesion are those of lichen simplex chronicus developed incidentally rather than deliberately.

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