Paroxysmal nocturnal hemoglobinuria and myelodysplastic syndrome: Disappearance of cytogenetic abnormalities

•Our report highlights the importance of PNH testing even in patients with an established MDS diagnosis when hypoplastic bone marrow and/or dysplasia with cytogenetic abnormalities are present.•It adds significant information on the complex link between MDS and PNH, suggesting that distinction between these entities may be difficult in some cases.•The transient presence of cytogenetic abnormalities is a unique characteristic of our patients’ course that needs to be further elucidated in larger studies of MDS and PNH patients. Paroxysmal nocturnal hemoglobinuria (PNH) is a rare life-threatening disease resulting from clonal hematopoietic stem cell evolution. There is a strong link between PNH and other acquired bone marrow failure syndromes, including myelodysplastic syndrome (MDS). Cytogenetic, morphological abnormalities or both are observed in the range of MDS/PNH diagnosis. Herein, we investigate cytogenetic abnormalities in PNH patients. We found two patients with PNH clones and MDS-associated abnormalities that later disappeared. The first patient, originally diagnosed with MDS and Trisomy 6, developed a large PNH clone. At the time of PNH diagnosis, the abnormal cytogenetic clone was no longer detectable despite persistent trilineage dysplasia. In the second patient, a large PNH clone and MDS-defining abnormality were detected at diagnosis, without evidence of dysplasia. No cytogenetic abnormalities were evident after complement inhibition. Our report adds significant information on the complex link between MDS and PNH, suggesting that distinction between these entities may be difficult in some cases. Especially in transplant eligible patients, the clinical phenotype may be the leading feature for treatment decisions in the era of complement inhibition. Lastly, the transient presence of cytogenetic abnormalities is a unique characteristic of our patients’ course that needs to be further elucidated in larger studies.