Transformed Mycosis Fungoides (MF) is a rare disease associated with an aggressive clinical course and shortened survival. Central nervous system (CNS) involvement has been sporadically described, with frequency between 1.3% and 11% and often diagnosed on postmortem setting. Given the rarity of CNS occurrence, we present a unique case of transformated MF with CNS relapse after Allogeneic Bone Marrow Transplantation (Allo-BMT).

We report a case of a 54 years-old male patient that was diagnosed with Mycosis Fungoides in 2016 and treated with systemic corticosteroids and PUVA until 2018 with slight improvement. In 2019, the lesions got worse and adenomegalies appeared. At that moment he was referred to our service. A biopsy of the inguinal lymph node was performed and diagnosis of Transformed Mycosis Fungoides was made with staging compatible with T4N3M0B0, and clinical stage IV A. At that time the patient didn't presented abnormal cell population in immunophenotyping of peripheral blood. He started methotrexate in weekly doses and presented a partial response after that. Treatment with brentuximab Vedotin (BV) followed by Allo-BMT was proposed. After 16 cycles of BV he presented a complete response at Positron Emission Tomography and Computed Tomography (PET-CT) and underwent haploidentical Allo-BMT with reduced intensity conditioning regimen (FLUMEL) and TBI. After Allo-BMT, he maintained complete response at PET-CT. After 14 months of Allo-BMT, the patient was readmitted to the service due to symptoms of headache, vomiting and right hemianopsia. Skull magnetic resonance imaging showed an expansive and infiltrative mass of 45 x 29 x 29 mm in the left parieto-occipital transition. Cerebrospinal fluid evaluation showed atypical cells on oncotic cytology with immunophenotyping showing 3% of mature lymphocytes with positive CD4 and negative CD7 and CD26. After 15 days of hospitalization, the patient had a subfalcine herniation and underwent emergency neurosurgery for lobectomy. The lobectomy material was sent to anatomopathological analysis and the immunohistochemistry showed neoplastic cells with expression of CD3 and CD4 and of loss of CD2, CD5, CD7 suggesting Mycosis Fungoides. A treatment with high dose methotrexate and intermediate dose of cytarabine was started. Patient is currently hospitalized in the Intensive Care Unit intubated due to alveolar hemorrhage on a postoperative setting.

We searched articles in the Pubmed database using the following MESH terms: “Mycosis fungoides”AND “central nervous system”between 1955 and 2021. We found 88 results and 52 matched criteria with patients with mycosis fungoides diagnosis with central nervous system commitment. It is known that CNS involvement by MF is infrequent and clinically detected CNS disease in MF patients is even rarer. Nguyen, GH recently reported a review describing 71 cases of confirmed CNS involvement in MF patients. No other cases have been reported since that publication. The aim of this case report is to show that aggressive T-cell neoplasias still have a very bad prognosis even with intensive approaches. The studies of new treatments are an urgent unmet need.