Introduction
Mycosis fungoides (MF) is the the most common cutaneous T-cell lymphoma. 3 variants are described in the last WHO 2018: folliculotropic, pagetoid and granulomatous slack skin. The evolution is chronic with a 5-year survival of 88%. The prognosis depends on age, clinical stage, and histological transformation into large cells. Pustular variants of MF (pMF) are rare. Isolated case reports suggest that pMF may have unfavorable prognosis. We conducted a prospective study of a series of pMF to further describe their clinical and pathological cahacteristics and outcome.
Methods
Prospective study, including all MF with histological pustules (follicular or not), diagnosed in expert center since 01/01/2019, and a literature review. Clinical and histological data, immunophenotype and clonality were collected using standardized datasheets. Outcomes of pMF were compared to another prospective cohort of non pustular MF (PHRC KIRs, n=78) established within the GFELC, from 2009 to 2011.
Results
We included 22 patients, representing 6.2% of all MF diagnosed in the expert center in the same period (n=352), associated with the 14 cases from litterature. In all, 78% (28/36) were men (male to femal ratio: 3.5/1), with a median age at diagnosis of 62.5 years (30 to 88 years). More than one biopsy was required in 61% (20/31) to establish the diagnostic of MF (median time before diagnostic: 14.5 months), with a diagnosis of inflammatory disease proposed at first in 24% (8/34) (3 suppurative acute folliculitis, 2 psoriasiform dermatitis and 2 pustular dermatitis). Clinically, 91% (31/34) had patches or plaque, 52% (18/34) pustules and 24% (8/34) flaking, suggestive of post-pustular desquamation (FigA). Progression towards tumor(s) (FigB), or lymphadenopathy, or visceral involvement developed in 78.6% of cases (22/28) (versus 9% (8/78) in KIRs’ cohort, p<0,001, OR: 0.03 with CI95% [0.01 ; 0.10]). 19 of 32 patients (59%) had a transformation in large cell lymphoma (versus 5% (4/78) in KIRs cohort, p<0,001, OR: 0.04 with CI95% [0.01 ; 0.14]), with a median of progression free survival of 24 months (0-180) (FigG). 17/31 patients died (61%), with an overall survival of 20 months (1-180) after pMF diagnostic (versus 6.4% (6/78) in KIRs cohort, p<0,001, OR: 0.05 with CI95% [0.01 ; 0.16]). In 55% of cases (17/31), the dermal infiltrates showed neutrophils. Corneal pustules (FigsC-E) and/or follicular pustules (FigsD-F) were observed in 87% (27/31) and 29% (9/31) of cases, respectively. A loss of CD7 expression was found in 25% (6/24) of pMF before transformation. A dominant T-cell clone was present in 74% (14/19) of all cases, versus 61.8% (48/78) of cases from the in KIRs cohort.
Conclusion
pMF follows an aggressive course, with a high risk of transformation or systemic involvement. Histopathological diagnosis is challenging because pMF may be confused with an inflammatory disease. At the pathophysiological level, it can be hypothesized that neutrophils in pMF may reflect an inflammatory or infectious background promoting malignant T-cell growth. Given the poor outcome of pMF, the presence of pustules in MF lesions needs to be stressed histopathologically and a more intensive therapeutic strategy should be considered in these patients.
