Origin Use of CD4, CD8, and CD1a Immunostains in Distinguishing Mycosis Fungoides from its Inflammatory Mimics: A Pilot Study

Patch-stage/early mycosis fungoides (MF) is difficult to differentiate from benign dermatoses, despite several robust histologic criteria. Most studies include advanced lesions and data about early disease is limited. OBJECTIVES: (1) To compare the CD4:CD8 ratio in patch-stage MF versus inflammatory mimics. (2) To study patterns of CD1a expression in the epidermis and dermis in the two groups. MATERIALS AND METHODS: Twenty cases each of early MF and inflammatory dermatoses were selected. The diagnoses were established after clinicopathologic correlation, repeat biopsies, and follow-up. The inflammatory group included pityriasis lichenoides chronica, actinic reticuloid, lichenoid purpura, and various psoriasiform dermatoses. Immunohistochemistry was done for CD4, CD8, and CD1a. Epidermal CD4, CD8 cells were quantified and CD1a was graded semi-quantitatively in the epidermis and dermis. RESULTS: The average CD4:CD8 ratio was 4.2 in MF (range: 1-16.8), and 0.9 in inflammatory diseases (range: 0.43-5), which was statistically significant (P < 0.0001). None of the MF cases had a ratio <1. Four cases of pityriasis lichenoides chronica had a ratio >1. CD1a cells had a continuous or confluent epidermal pattern in almost all cases of MF, while they occurred as small or large groups in the dermis. In inflammatory dermatoses, there were either isolated or scattered CD1a+ cells in both epidermis and dermis. CONCLUSIONS: Elevated CD4:CD8 ratio favors MF. But there is an overlap in the lower range with pityriasis lichenoides chronica. These cases require good clinicopathologic correlation and follow-up. Patterns of CD1a expression are more reliable. Immunostains buttress morphology and are a valuable addition.