Interstitial granuloma after interferon-gamma and narrowband UVB therapy in a patient with mycosis fungoides: Immunological and histopathological considerations.

In mycosis fungoides (MF), cutaneous granuloma formation is unusual. Furthermore, MF showing interstitial granuloma, a rare type, after combination therapy with interferon-gamma (IFN-γ) and narrowband UVB (nbUVB) has not been previously reported. A 77-year-old man was referred to our hospital with a 2-month history of erythroderma. Biopsied specimens revealed infiltration of atypical lymphocytes and eosinophils. A diagnosis of an erythrodermic variant of MF was made. He was treated with combination therapy of IFN-γ and nbUVB. After the therapy, papules newly appeared and a histopathological specimen revealed interstitial granuloma. There were several CXCR3-positive cells around the granuloma. We speculated that the combination therapy made T-helper 1 cells migrate to the cutaneous lesion and resulted in the granuloma formation. Furthermore, judging from the disappearance of elastic fibers around the interstitial granuloma, we considered that IFN-γ may induce the infiltration of histiocytes interstitially after damage of elastic fibers caused by nbUVB therapy, and both IFN-γ and nbUVB may thus play an important role in the histogenesis. Not only histopathology but also immunological observations are needed to elucidate the mechanisms underlying the development of different types of granuloma in MF.