Quiz 12: What is your diagnosis?

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Diagnosis: Quiz 12

Quiz 12

Answer: Lichen planus-like keratosis

Criteria for diagnosis histopathologically: Zones of compact orthokeratosis with foci of parakeratosis, acanthosis, and hypergranulosis, together with a dense band-like infiltrate of lymphocytes obscuring the dermoepidermal junction, and signs of vacuolar alteration with necrotic keratocytes in the basal layer are concordant with lichen planus-like keratosis.

Differential diagnosis histopathologically: Lichenoid infiltrates of lichen planus, lichenoid drug eruption, and lichenoid lupus erythematosus have to be excluded. 

Criteria for diagnosis clinically: A single erythematous, flat plaque on the chest is a stereotypical expression of lichen planus-like keratosis.

Differential diagnosis clinically: Clinically lichen planus-like keratosis is often misdiagnosed as basal cell carcinoma.

Clinicopathologic correlation: The plaque is a result of the acanthosis and hypergranulosis and of the dense lymphocytic infiltrate at the dermoepidermal junction. The scaly surface corresponds histopathologically to zones of hyperkeratosis and parakeratosis

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

1) Compact orthokeratosis with foci of parakeratosis, variable presence of acanthosis, foci of hypergranulosis, and a dense band-like infiltrate of lymphocytes in combination with solar elastosis in the papillary dermis are criteria for the diagnosis of lichen planus-like keratosis. Those findings may be indistinguishable from lichen planus, and a clinical-pathologic correlation often is necessary to resolve this issue.

2) Lichen planus-like keratosis represents one stage in the regression of a solar lentigo or reticulated seborrheic keratosis. The dense lichenoid lymphocytic infiltrate is an expression of this process. Often, a residuum of the pre-existing solar lentigo or reticulated seborrheic keratosis can be seen at the edges of the lesion.

3) The distinction between lichen planus-like keratosis and lichen planus can be challenging. In sections prepared from shave biopsies one clue is the extension of the lichenoid infiltrate from one edge of the section to the other. Lesions of lichen planus are usually sampled by punch biopsy in which the lichenoid inflammatory infiltrate does not extend to the edges of the section. The clinical history of a solitary lesion on a sun-exposed site on the trunk is another clue to the diagnosis.

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