Persistent pigmented purpuric dermatitis and mycosis fungoides: simulant, precursor, or both? A study by light microscopy and molecular methods.

Mycosis fungoides (MF) can present with purpuric lesions, and rare patients who seemed to have persistent pigmented purpuric dermatitis (PPPD) have developed MF. We recently encountered two patients referred to our cutaneous lymphoma clinic who had PPPD rather than MF and two others who appeared to have both conditions, leading us to explore the histologic similarities of these diseases. We examined specimens from 56 patients with PPPD to determine the frequency of MF-like histologic configurations, namely, the psoriasiform lichenoid, psoriasiform spongiotic lichenoid, and atrophic lichenoid patterns. We also noted the degree of spongiosis, epidermotropism, papillary dermal fibrosis, lymphocytic atypia, and epidermal hyperplasia, the number of extravasated erythrocytes and siderophages, and the distribution of lymphocytic infiltrate within the epidermis. In 29 of 56 patients, there were patterns typically seen in MF. PPPD can feature lymphocytes aligned along the epidermal side of the dermoepidermal junction, with few necrotic keratinocytes, as can MF. Papillary dermal edema occurred frequently in PPPD but not in MF, while lymphocytes in MF but not PPPD had markedly atypical nuclei and had ascended into the upper spinous layer. Given these similarities, we tested for clonality of the T-cell population using a polymerase chain reaction assay for gamma-chain rearrangements. Clonal populations were present in three of three and one of two specimens from patients with both PPPD and MF, but also in 8 of 12 specimens typical of lichenoid patterns of PPPD. These findings raise the possibility that the lichenoid variants of PPPD are biologically related to MF.