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Pityriasis lichenoides: a clonal T-cell lymphoproliferative disorder
Cynthia Magro1, A Neil Crowson, Al Kovatich
1Department of Pathology Ohio State University Medical Center, Columbus, OH 43210, USA.
Human Pathology
|August 31, 2002
Summary
Pityriasis lichenoides (PL) may be a T-cell dyscrasia, not just a reactive dermatosis. Research found atypical T-cells and clonality in PL, suggesting links to mycosis fungoides (MF) and large plaque parapsoriasis (LPP).
Area of Science:
- Dermatopathology
- Immunodermatology
- Oncodermatology
Background:
- Pityriasis lichenoides (PL) is typically classified as a reactive dermatosis.
- However, associations with large plaque parapsoriasis (LPP) and mycosis fungoides (MF), along with lymphoid atypia and T-cell clonality in PL lesions, suggest a potential T-cell dyscrasia.
Purpose of the Study:
- To investigate the hypothesis that Pityriasis lichenoides (PL) represents a form of T-cell dyscrasia.
- To analyze the immunophenotypic and molecular characteristics of T-cells within PL lesions.
Main Methods:
- Review of 35 dermatopathology cases diagnosed with Pityriasis lichenoides chronica (PLC) and/or Pityriasis lichenoides et varioliformis acuta (PLEVA).
- Hematoxylin and eosin staining, immunophenotyping (CD2, CD3, CD4, CD5, CD7, CD8, CD20, CD30, CD56), and T-cell receptor (TCR)-gamma chain rearrangement analysis via PCR single-stranded conformational polymorphism.
- Clinical correlation, including tracking progression to MF or LPP.
Main Results:
- Five patients progressed to conditions consistent with MF and/or LPP.
- Biopsies revealed T-cell tropism to the epidermis with characteristic changes; epidermal atrophy and cerebriform cells were noted in chronic PLC, correlating with MF progression.
- A T-cell dominant infiltrate was observed, with CD7 deletion in 21/32 biopsies, particularly in atypical intraepidermal CD4+ cells. CD8+ lymphocytes showed directed migration patterns. Clonality was detected in 25/27 evaluable biopsies.
- Aberrant T-cell phenotype (CD4+, CD5-, CD7-) was identified, similar to MF.
Conclusions:
- The findings of intraepithelial atypical lymphocytes, phenotypic abnormalities, and TCR-gamma rearrangements support the classification of PLC and PLEVA as T-cell dyscrasias.
- PL lesions may exhibit a recalcitrant course, characteristic of MF and pre-mycotic disorders like LPP.
- An abnormal immune response to an antigenic trigger is suggested as the inciting event for this T-cell dyscrasia.