Microcytosis in Myelofibrosis with Myeloid Metaplasia: Prevalence and Clinical Correlates.

Background:

Microcytosis is a characteristic laboratory feature for both iron deficiency anemia and thalassemia. Microcytosis is also infrequently seen with “anemia of chronic disease”. A partial list of the latter include rheumatoid arthritis, polymyalgia rheumatica, diabetes mellitus, connective tissue disease, chronic infection, Hodgkin’s lymphoma, Castleman’s disease, and renal cell carcinoma. In the current study, we show that microcytosis is a frequent laboratory feature in myelofibrosis with myeloid metaplasia (MMM) and investigate its clinical relevance in the particular setting.

Methods:

In order to minimize the confounding effects of nutritional deficiencies, red blood cell transfusion, and drug therapy on mean corpuscular volume (MCV), the current study was limited to young patients (age < 60 years) that had not received either red blood cell transfusion or drug therapy for MMM during the time of their initial laboratory investigation.

Results:

The study population consisted of 102 consecutive patients with MMM (median age 51 years, range 18–60) including 60 males. At diagnosis, the median (range) values for hemoglobin, leukocyte count, and platelet count were 11 gm/dL (7.4–14.9), 8.3 x 10⁹/L (1–40) and 357 x 10⁹/L (14–1512), respectively. Spleen measurements were documented in 78 patients (median 6 cm below the left costal margin, range 0–24) and the incidence of hypercatabolic symptoms was 18% (12 of 67 evaluable patients). The Dupriez prognostic score distribution included low-risk (n=73), intermediate-risk (n=19), and high-risk (n=10) disease categories.

The overall incidence of microcytosis (MCV < 80 fL) was 28%; median MCV was 84.3 fL (range, 60.6–99.1). Among the 28 patients with microcytosis, MCV was less than 70 fL in 4 patients. Concomitant serum ferritin levels were available in 44 patients (median, 92 μg/L; range, 4–6440) and the levels were below 30 μg/L in 7 patients including 4 with microcytosis. Bone marrow iron stains were sporadically performed and showed normal iron stores in the majority of evaluable cases. The study cohort was followed for a median of 70 months (range 0–300). Multivariate analysis of variable that were measured in all study patients identified anemia, thrombocytopenia, and age but not MCV as independent prognostic indicators of inferior survival. The addition of variables that were measured in a variable proportion of the study population disclosed additional prognostic value for hypercatabolic symptoms and abnormal cytogenetics. Interestingly, microcytosis was significantly associated with the absence of cytogenetic abnormalities (p=0.04); among the 10 patients with abnormal cytogenetic findings, 9 had an MCV of ≥ 80 fL. Microcytosis did not correlate with several other clinical and laboratory features including gender, presence of hypercatabolic symptoms, spleen size, hemoglobin level, platelet count, leukocyte count, serum lactate dehydrogenase level, and the Dupriez prognostic score.

Conclusion:

Microcytosis with a normal or elevated serum ferritin level is a frequent laboratory feature in MMM but does not appear to influence survival. The observation regarding the low incidence of cytogenetic abnormalities in MMM patients with microcytosis is intriguing but requires validation by a prospective study. Whether or not MMM-associated microcytosis represents an acquired defect of globin synthesis, as might be the case in some patients with myelodysplastic syndrome, remains to be elucidated.