After 1.5 years of treatment with dimethyl fumarate (DMF) for multiple sclerosis, preceded 8 years earlier by intravenous (IV) cladribine and 1 year earlier by natalizumab, our patient developed myelodysplastic syndrome (MDS). The initial manifestation was a severe drop in absolute neutrophil and lymphocyte counts. Repeat bone marrow biopsy demonstrated a new unbalanced translocation (between the chromosome 1 long arm and chromosome 7 short arm). This case report, to our knowledge, is the first linking iatrogenic MDS to DMF and cladribine, while also suggesting caution with immunosuppressants in multiple sclerosis patients.
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