Paroxysmal nocturnal hemoglobinuria as a marker for clonal myelopathy.

Paroxysmal nocturnal hemoglobinuria (PNH) is recognized as a clonal disorder manifested as increased sensitivity of marrow cells to complement. Case reports have associated this condition with leukemia, myelodysplasia, and myeloproliferative disorders. We identified 47 patients with PNH from 1976 to 1990. In 9 of the 47 patients, PNH was associated with another clonal myelopathy. Five patients had PNH and a myelodysplastic syndrome, and four had PNH and agnogenic myeloid metaplasia. PNH preceded the development of myelodysplastic syndrome but occurred after the development of agnogenic myeloid metaplasia. This is the largest series of PNH and other clonal myelopathies. We suggest that the PNH defect may represent a second manifestation of a single stem cell disorder.