Pityriasis Lichenoides Chronica

The pattern is typical for pityriasis lichenoides chronica including the thick ichthyotic-like parakeratotic scale, pattern of psoriasiform epidermal hyperplasia, unusual tropism of lymphocytes and histiocytes through the more superficial layers of the epidermis accompanied by a superficial lymphocytic purpuric vascular reaction with overall mild lymphoid atypia. Mycosis fungoides can develop in a background of pityriasis lichenoides; however, the lymphoid atypia is insufficient to warrant categorization as mycosis fungoides.

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Slide 1: 16 year-old female with bilateral medial thigh lesions. The biopsy shows a mild epidermal hyperplasia whereby there is overlying striking hyperkeratosis with prominent parakeratosis.

Slide 2: There is infiltration of the epidermis by lymphocytes. As well there is an admixture of histiocytes. There is also a supervening angiocentric lymphohistiocytic infiltrate within the superficial corium.

Slide 3: There is infiltration of the epidermis by lymphocytes. As well there is an admixture of histiocytes. The lymphocytes exhibit a somewhat haphazard pattern of infiltration of the epidermis with a predilection to migrate towards the more superficial aspects of the epidermis whereby the lymphocytes are intimately admixed with histiocytic forms.

Slide 4: There is infiltration of the epidermis by lymphocytes. As well there is an admixture of histiocytes. The lymphocytes exhibit a somewhat haphazard pattern of infiltration of the epidermis with a predilection to migrate towards the more superficial aspects of the epidermis whereby the lymphocytes are intimately admixed with histiocytic forms.

Slide 5: CD3 immunostain. Comprehensive phenotypic studies were performed. The infiltrate was highlighted by Beta F1 and the pan T cell markers CD2, CD3 (shown here), and CD5.

Slide 6: CD8 immunostain. There was a predominance of CD8 lymphocytes within the epidermis compared to those of the CD4 subset whereby the CD4 to CD8 ratio is likely in the realm of 1:3.

Slide 7: CD5 immunostain. The histopathology is quite characteristic of pityriasis lichenoides chronica. From a cytomorphologic perspective the lymphocytes are small in size, appearing somewhat hyperchromatic with some degree of nuclear contour irregularity.