Quiz 56: What is your diagnosis?

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Diagnosis: Quiz 56

Quiz 56

Answer: Solar lentigo

Criteria for diagnosis clinically: A J-shaped brown lesion, mostly macular at the hook and papular along the long axis, is a solar lentigo in the midst of other solar lentigines.

Differential diagnosis clinically: There is none.

Criteria for diagnosis histopathologically: On the left side of this section of tissue, as viewed at scanning power magnification, are nubbins of keratocytes pigmented prominently, and in the center and on the right is a lesion papillate made up of similar-appearing keratocytes pigmented by melanin, but less apparently than on the left, exhibiting a thickened cornified layer that has maintained its basket-woven configuration-the findings, in toto, being those of solar lentigo at different stages in its development.

Differential diagnosis histopathologically: There is none. 

Clinicopathologic correlation: The lesion is brown because of the increase in the amount of melanin within epidermal keratocytes; the hook of the "J" is flattish because the epidermis is but slightly thickened there; the long axis has a slightly mammillate surface because of the papillations observable histopathologically; and the surface is smooth because the cornified layer, although thickened, too, has maintained its basket-woven pattern.

Options for therapy predicated on knowledge of histopathologic findings: The lesion is benign and, therefore, no additional surgery is warranted.

1) What is pictured here, clinically and histopathologically, illustrates well the evolution of a single pathologic process, it being known conventionally at the outset as  solar lentigo and later in its development as seborrheic keratosis. We unconventionally consider this benign neoplasm to be a single pathologic process and for that reason give it, in its entirety, a single name-solar lentigo.

(2) The authentic  seborrheic keratosis that occurs especially on the trunk of older persons is independent completely of a solar lentigo, coming into existence as it does wholly removed from the effects of ultraviolet radiation. Just the opposite is the case for solar lentigo; in every instance, it is brought about by the effects of UVR, usually in the form of sunlight.

3) Because the condition known universally as  seborrheic keratosis beginning as a solar lentigo and the one deemed universally to be seborrheic keratosis originating de novo and independent of a solar lentigo are patently different conceptually, clinically, and histopathologically,it is confusing to diagnose both of them as "seborrheic keratosis." The former should be known as solar lentigo, understanding full well that some flat examples will, in time, progress to a lesion elevated and papillate, it vaguely resembling seborrheic keratosis histopathologically as it presents itself on a trunk. Only the latter can, and should, be designated rightfully seborrheic keratosis.

4) Some solar lentigines are typified by large and monomorphic nuclei. Although that lesion has been termed  large-cell acanthoma by some dermatopathologists, it is nothing other than a solar lentigo.

5) When a solar lentigo, usually one in the skin in the vicinity of the sternum and usually in older individuals, attracts to it a lichenoid infiltrate of lymphocytes, the effects of which result in regression of the benign neoplasm of pigmented keratocytes, the lesion has been designated  lichen planus-like keratosis. In actuality, a so-called lichen planus-like keratosis is nothing other than a solar lentigo in the process of involution secondary to the influence on it of products of lymphocytes.

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