Clone to the rescue: a challenging case of granulomatous mycosis fungoides diagnosed by gene rearrangement studies.

Granulomatous mycosis fungoides (MF) poses multiple diagnostic challenges, which commonly delay diagnosis. The clinical morphology of the lesions mimic other granulomatous disorders. Biopsy findings of lymphocyte epidermotropism and an elevated CD4:CD8 ratio are suggestive of MF, but are not always noted.1 We present a patient with a decade-long history of progressive ulcerating plaques who was ultimately diagnosed with granulomatous MF using T-cell receptor rearrangement (TCR) studies. A 74-year-old man with a history of sun-damaged skin and stage 1A melanoma presented to dermatology clinic for an 11-year history of progressive indurated plaques on the arms, legs, face and trunk. The lesions were asymptomatic and began as pink atrophic macules on the arm that progressed into enlarging hard sclerotic plaques. Prior extensive workups at multiple institutions had been inconclusive. Four biopsies had been performed during his disease course, all of which showed dense dermal necrotising and mixed granulomatous inflammation. Mycobacterial, fungal and bacterial tissue cultures had been negative. Studies including fungal serology panels, purified protein derivative, liver function testing, complete blood count, serum protein electrophoresis and chest X-ray were unremarkable. Due to past presumed diagnoses of sarcoidosis, necrobiosis lipoidica, superficial fungal infection and granuloma annulare, he had trialled a series of ineffective treatments including high-potency topical steroids, intralesional steroids, V-beam laser, topical antifungals, topical calcineurin inhibitors, oral tetracyclines and oral dapsone. Initial examination revealed pink …