Essential thrombocythemia with ringed sideroblasts: a heterogeneous spectrum of diseases, but not a distinct entity

According to the recently published WHO-classification essential thrombocythemia with ringed sideroblasts (ET/RS) remains an ambiguous category which may be considered as myelodysplastic/myeloproliferative disease, unclassifiable. Because until now only case reports or very small series of patients have been described, a more systematically performed study is warranted.

A retrospective evaluation was carried out on 38 patients with the diagnosis of ET/RS and more than 15 % ringed sideroblasts on smears. Simultaneously performed bone marrow biopsies, follow-up examinations and survival data were also available.

Based on cytological features and particular bone marrow findings including immunohistochemistry three patterns could be determined. These were associated with different clinical features and in particular prognosis. Group I included six patients whose diagnosis was consistent with ET, group II comprised 21 patients revealing prefibrotic and early fibrotic chronic idiopathic myelofibrosis (CIMF) and finally 11 patients (group III) displayed myelodysplastic syndromes (MDS). Follow-up studies revealed that no patient with ET showed a fiber increase but eight CIMF patients developed overt myelofibrosis and four patients of the MDS group developed secondary acute myeloid leukemia. In comparison with a control group of 39 patients with true ET, prognosis was significantly different because our cohort showed a median survival of 100 months that contrasted significantly with the 170 months in the patients with true ET.

Ringed sideroblasts are not a pathognomonic feature of MDS, but may indicate a dysplasia probably associated with a primary or secondary disturbance of iron metabolism in a variety of disorders. For this reason, a more accurate classification of so-called ET/RS patients is warranted by evaluation of smears and in particular bone marrow biopsy specimens. According to our findings these patients should be classified as having either ET, CIMF or MDS and show a significantly different survival pattern.