Which came first, purpuric mycosis fungoides or pigmented purpuric dermatosis? A diagnostic dilemma

Pigmented purpuric dermatoses (PPD) are a unique group of vascular disorders with a range of clinical presentations of unknown aetiology. They have a unique histopathological profile, however overlap with a rare form of mycosis fungoides (MF) called purpuric MF. Purpuric MF cannot be excluded on histology and often requires an additional T cell gene re‐arrangement study to further delineate the diagnosis. This study is often out of pocket for the patient and may mislead as there are rare variants of PPD that exhibit monoclonality. In this poster we discuss the case of a 51 year old man who presented with a clinical and histopathological diagnosis of PPD, which on T cell gene re‐arrangement study demonstrated a clonal T cell population which could be consistent with a lymphoproliferative disorder like purpuric MF. We offer clinical photographs since his initial presentation, his biopsy histopathology slides and his T cell gene re‐arangement study. We also gleam valuable insight from a dermatopathologist's interpretation and advice on this case. This case serves to highlight the limitations of our current diagnostic modalities in accurately distinguishing PPD and MF, and aims to add to the literature to enable us to formulate more comprehensive diagnostic definitions and gain a better understanding of the relationship between these two conditions.