Search

Introduction: Mycosis fungoides (MF) is the most common type of primary cutaneous T cell lymphoma. Many clinicopathological variants of MF have been described in the literature, though only a few presented in a segmental pattern. There are several unique patterns of distribution of skin diseases, one of which is the Blaschko Lines. Congenital skin diseases develop in a Blaschkoid pattern due to mosaicism. In contrast, according to Happle, the development of acquired skin diseases in a similar pattern is explained by superimposed segmental manifestation - a process which involves mosaicism overlapping a preexisting congenital mutation. The theories by which previous case reports explained the segmental appearance of MF did not cover the molecular basis for their development. We report a case of a patient who presented with MF in a unique segmental distribution consistent with the Blaschko lines. The patient was found to have an acquired mosaic mutation in GNAS gene exclusively in the involved skin which represents a superimposed segmental manifestation according to Happle's theory. This case demonstrates the hidden potential of these rare cases which allows a better understanding of the pathogenesis by which acquired diseases develop. This is a basis for further research that could help identify new therapeutic targets for MF and other diseases that share its genetic etiology.

Mycosis fungoides (MF) is the most prevalent cutaneous lymphoma, characterized by uncontrolled growth of T cells within the skin. The diagnosis in the early stages may be difficult, since, in these stages, the disease can imitate benign inflammatory processes, both clinically and histologically. One of the difficulties in determining diagnostic criteria for early MF is the existing terminology of parapsoriasis. There is disagreement concerning the exact definition and whether it is a chronic benign condition with similar clinical and histological characteristics as MF, or rather it is part of the disease spectrum itself. There is a need for uniformity in the definition for treatment decisions, for epidemiological purposes and for clinical and experimental research. This article reviews the different approaches to parapsoriasis as part of MF over the years.