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Pityriasis rubra pilaris ("checkerboard sign")

Differential Diagnosis

Except for attributes of the cornified layer, this psoriasiform dermatitis could be confused with psoriasis.

Alternation of orthokeratosis and parakeratosis in both vertical and horizontal directions is decisive for pityriasis rubra pilaris.

References

Ackerman AB. Sherlock Holmesian dermatopathology: Parakeratosis as a diagnostic clue. Am J Surg Pathol 1978;2:71-80.147632

Ragaz A, Ackerman AB. Evolution, maturation and regression of lesions of psoriasis. Am J Dermatopathol 1979;1:199-214.543520

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