Mycosis Fungoides and Granulomatous Slack Skin: A Single Entity With Distinct Clinical Phenotypes.

Granulomatous cutaneous T-cell lymphoma includes mycosis fungoides with significant granulomatous inflammation (GMF) and granulomatous slack skin (GSS), listed in the WHO classification as a subtype of mycosis fungoides (MFs). 1 These overlapping entities have shared clinical and histopathologic features which can present a diagnostic challenge. The dominance of the granulomatous infiltrate and the often sparse lymphocytic infiltrate frequently with minimal cytological atypia are features that distract from the correct diagnosis, even when raised by the clinician. We describe the clinical and histopathologic characteristics of 3 cases of granulomatous cutaneous T-cell lymphoma, illustrate the close clinical and pathologic relationship between GMF and GSS and emphasize the diagnostic difficulties that the granulomatous infiltrate can present. Furthermore, we demonstrate, for the first time, considerable elastolysis in a significant proportion of classical (Alibert-Bazin) MF lesions and therefore postulate that the differences observed between GMF and GSS are one of degree and secondary to their anatomic location rather than reflecting meaningful separate entities.