Epidemiology of the Myelodysplastic Syndromes
The true incidence of the myelodysplastic syndromes (MDS) is not known because these disorders were defined only relatively recently. The 9th edition of the International Classification of Diseases (ICD-9) (published in 1977) (1) did not recognize them as distinct nosological entities, and therefore they tended to get lost under a variety of headings. Chronic myelomonocytic leukemia (CMML) was included in ICD-9, but only as a variety of chronic myeloid leukemia (ICD-9 code 205.1). In addition, in the ICD-9 manual, the term “myelodysplasia” refers to congenital defects of the spinal canal, further confusing the matter. The more specialized diagnostic manual, the International Classification of Diseases for Oncology (ICD-O series), suffers from similar defects. Therefore, cancer registries, death certificates, and hospital discharge data have been of little value in establishing the prevalence of MDS. Indeed, the nonuniform classification schemes for MDS are exemplified by a Swedish study that found MDS recorded in cancer registries under five different diagnoses (2).