Abstract:

Mycosis fungoides (MF) represents the most common type of primary cutaneous T-cell lymphoma. Recognition of MF variants with divergent immunophenotypes is important for accurate diagnosis and appropriate management, as they can be confused with other lymphoma subtypes. We present a case of a 49-year-old male previously diagnosed with a cutaneous lymphoproliferative disorder with an unusual NK/T-cell phenotype. He presented with a 10-year history of pelvic girdle rash including involvement of the right hip and right upper thigh. The clinical lesions were characterized as atrophic patches, particularly more accentuated in sun-protected areas. Approximately 10% of the body surface was involved. Shave biopsies revealed an atypical epidermotropic lymphocytic infiltrate that included a band-like pattern in the superficial reticular dermis, and was associated with fibroplasia. The epidermotropic cells included hyperchromatic small to medium sized lymphocytes, with perinuclear halos, and ‘tagging’ along the dermal-epidermal junction. Rare small intraepidermal microcollections of lymphocytes were also seen. The immunophenotype, however, was unusual in that the neoplastic lymphocytes showed complete loss of pan T-cell antigens (CD2, CD3, CD5, CD7, CD4, CD8, TCR-beta, TCR-gamma) along with expression of CD56, CD43, cytotoxic markers (TIA-1, granzyme B and perforin), and weak CD20. All other B-cell markers were negative. In situ hybridization for EBV RNA was negative, and the proliferation index by Ki-67 staining was very low (<5%). T-cell gene rearrangement studies demonstrated clonal gamma chain gene rearrangement. The combination of clinical findings, in addition to the histopathologic and immunophenotypic profile, were diagnostic of null T-cell phenotype MF with aberrant expression of CD56 and CD20. Null T-cell phenotype MF is very uncommon, can be diagnostically challenging, and mislead to the diagnosis of aggressive lymphoma subtypes.

Financial Disclosure:
No current or relevant financial relationships exist.

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Regina Burton, MD