Secondary myelodysplastic syndrome after hydroxychloroquine therapy.

Primary myelodysplastic syndromes (MDS) occur in the absence of exposure to ionizing radiation, chemotherapeutic agents or myelotoxic drugs, whereas secondary MDS occurs in the presence of such exposure. We encountered 4 patients among 217 patients on hydroxychloroquine for rheumatological conditions in 2005 diagnosed with MDS. Two patients were male and two were female; the median age was 69.75 years, (range 65-76). The dose of hydroxychloroquine for all patients was 400 mg daily with median treatment duration of 10.5 years and a range of 6-16. All patients had bone marrow biopsy confirmation of the diagnosis of MDS. The incidence of MDS in a group older than 70 years ranges from 15 to 50/100,000 persons per year. The diagnosis of 4 cases of MDS among 217 patients in 1 year is approximately 123-137-fold higher than the risk of MDS in the general population aged more than 70 years (P < 0.001) and suggests that long-term treatment with hydroxychloroquine is associated with an increased risk of developing secondary MDS.