Quiz 16: What is your diagnosis?

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Diagnosis: Quiz 16

Quiz 16

Answer:  Solar lentigo

Criteria for diagnosis histopathologically: Orthokeratosis, nubbins of pigmented epidermal keratocytes, and a slightly increased number of melanocytes at the dermoepidermal junction are features of a solar lentigo.

Differential diagnosis histopathologically: There is none. 

Criteria for diagnosis clinically: A tan, sharply circumscribed macule on sun-damaged skin is characteristic of a solar lentigo or flat seborrheic keratosis.

Differential diagnosis clinically: Clinically this lesion could be a basal cell carcinoma, Bowen`s disease or, given the close proximity of a scar, even a melanoma. Biopsy is necessary to come to the correct diagnosis. 

Clinicopathologic correlation: The central, irregularly pigmented papule is mirrored by a thickened epidermis with basal melanin hyperpigmentation.

Options for therapy predicated on knowledge of histopathologic findings: The lesion is benign and therefore no therapy is needed. 

1) Solar lentigo and reticulate seborrheic keratosis are different names for the same pathologic process at different stages of its development.

2) They usually develop on sun-damaged skin and therefore the presence of solar elastosis in the upper part of the dermis is typically seen by light microscopy.

3) Horn pseudocysts are tunnels of infundibular epidermis that contain corneocytes arranged in either basket-woven or laminate fashion, or both. They are characteristic of seborrheic keratosis but have not formed yet in solar lentigo, in which orthokeratosis with corneocytes arranged in laminated fashion is usually present.

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