Epidermotropic secondary cutaneous involvement by relapsed angioimmunoblastic T-cell lymphoma mimicking mycosis fungoides: a case report.

Angioimmunoblastic T-cell lymphoma (AITL) is frequently associated with skin lesions, but epidermotropic cutaneous involvement has never been described. A 37-year-old man presented with erythematous and pruriginous plaques, clinically suggestive of mycosis fungoides, distributed all over the body, 3 weeks after the last line of a polychemotherapy, given for an AITL diagnosed 1 year earlier on a lymph node biopsy. Skin biopsy showed an epidermotropic CD4(+) T-cell lymphoma, so that a diagnosis of mycosis fungoides was first proposed. Further investigations showed that atypical lymphocytes strongly expressed CD10 and markers of follicular helper T cells (T(FH) ) including PD1, BCL-6 and CXCL13. The diagnosis of an unusual epidermotropic cutaneous localization of the AITL was finally made, supported by the presence of the same T-cell clone in the initial lymph node biopsy and the skin. We therefore recommend performing markers of T(FH) cells in patients with unusual epidermotropic cutaneous T-cell lymphomas, particularly if they have any clinical features suggestive of AITL.