Pigmented purpura dermatosis-like mycosis fungoides: four case reports and a review of published cases.

Mycosis fungoides (MF) is the most prevalent type of cutaneous T-cell lymphoma and is generally characterized by multiple patches or plaques with fine scales. One of its variants manifests with multiple purpuric eruptions, mimicking benign pigmented purpuric dermatosis (PPD). To investigate clinicopathological features of PPD-like MF patients. We report four PPD-like MF cases and summarize the clinicopathological features described in reports of nine PPD-like MF cases published in the past 20 years. Compared with benign PPD, petechial lesions in PPD-like MF are more generalized, persistent, and resistant to conventional steroid treatment. Histologically, a superficial dermal band-like infiltrate of atypical lymphocytes with epidermotropism seems to be the most common feature of PPD-like MF. A lymphoid phenotype of CD4+ CD7- T cells and a monoclonal T-cell profile, demonstrated by T-cell receptor gene arrangement analysis, favour a diagnosis of PPD-like MF. Although the exact relationship between PPD and PPD-like MF remains unclear, our study has attached importance to the differential diagnosis of the two diseases in cases of overlooked MF variants. If persistent or generalized purpuric lesions are present, PPD-like MF should be taken into consideration. A thorough physical examination combined with pathological findings may lead to a correct diagnosis.