Making a differential diagnosis between early
mycosis fungoides and
parapsoriasis is often difficult at the clinical and histological level. The aim of this study was to explore markers that could help in this process. A total of 88 patients were included in 2 categories: large plaque
parapsoriasis and digitiform
parapsoriasis. A histological examination was performed for each patient, and expression of the
antigen My7 (CD13), which is lacking in cutaneous T-
lymphomas (but not in inflammatory lesions) and rearrangement of the T-cell receptor gene were analysed. A histological aspect of epidermotropic
cutaneous T-cell lymphoma was observed in 23.5% of cases of large plaque
parapsoriasis and 15% of cases of digitiform
parapsoriasis. A disappearance of My7
antigen was noted in the 2 forms of
parapsoriasis, more frequently when there was
cutaneous T-cell lymphoma histology. A cutaneous clone was observed in 10.3% of cases of large plaque
parapsoriasis, but not of digitiform
parapsoriasis. For 3 patients, a cutaneous clone and a disappearance of My7 were associated with a non-specific histology. Considering these histological, immunological and molecular
biological data, it appears that My7
antigen combined with T-cell clone may help the dermatologist to confirm the diagnosis of early
mycosis fungoides. Moreover, further studies will determine whether CD13 is an early prognostic marker of evolution of a
parapsoriasis to
mycosis fungoides. Finally, these results demonstrate that digitiform
parapsoriasis can be an early stage of MF.