T2* MRI Provides No Evidence for Myocardial and Pancreatic Iron Overload in Multitransfused Patients with Sickle/β-Thalassemia.

Introduction: Transfusion-dependent hemolytic anemias particularly thalassemia major (thal.m) and also sickle cell disease (SCD) result in iron deposition in the reticuloendothelial system in major organs, mainly in the liver and also in the heart and endocrine glands. However, liver iron levels in patients with thal.m measured by other techniques were found to have no predictive values for the extent of their cardiac iron deposition. T2* MRI sequences have been previously addressed as a reliable tool for non invasive evaluation of iron load in the liver, heart and pancreas. Patients with T2* value > 20 ms have normal cardiac function while the prevalence of myocardial dysfunction and arrhythmias increases as a consequence of cardiac iron overload (T2* < 20 ms). A previous study comparing cardiac iron overload in transfusion dependent thal.m and SCD patients matched for age and liver iron content, found abnormally low cardiac T2* values (<20 ms) in nearly 40% of patients with thal.m, while the T2* values were normal in the patients with SCD (1) (

Patients and Methods: Eleven patients with sickle/β-thal., 3 males and 8 females, mean age 31 years ± 9.5 (SD) were analyzed, 6 of them were splenectomized. Their mean ± SD values for hemoglobin was 9.0 gr/dl, for serum ferritin - 3900 ng/ml ± 3944 and for transferrin saturation - 80% ± 23. All of them were transfused and received a mean of 97 packed cell units ± 88 (SD). Only one patient received iron chelation for 10 months until 6 months prior to entering the study. Seven patients received regularly Hydrea 1–1.5 gr/day for > 10 years. MRI evaluation (1.5T, GE MRI system) included: Left ventricular (LV) function (ejection fraction)- steady-state free procession (SSFP) cine sequence as well as iron load quantification- breath-hold multi echo gradient echo T₂*, sampled across regions of interest in the LV septum, liver parenchyma and pancreatic tissue. (

Results: All patients had normal T2* values in the heart (>20ms) and in the pancreas (>30ms). The left ventricular ejection fraction, left ventricular endsystolic and endiastolic volumes (evaluated both by echo-cardiography and by cine function MRI) were normal in all patients. There was no evidence for pleural or pericardial effusion. The diameter of the pulmonary artery and right ventricle were normal. Seven patients demonstrated evidence of mild to moderate iron deposition in the liver (T2* <6.3 ms). In these patients mean serum ferritin (5656 ng/ml) and transferrin saturation (92.4%) were significantly higher (p=0.001) than in 4 patients with normal T2* levels in the liver (>6.3ms) where mean serum ferritin was 872ng/ml and transferrin saturation 59.5%.

Conclusion: The T2* MRI values of 11 patients with sickle/β-thal. showed that whereas 7 patients had a certain degree of iron deposition in the liver, none demonstrated cardiac or pancreatic iron deposition. Therefore, with respect to iron deposition, multitransfused patients with sickle/β-thal. are similar to patients with homozygous SCD and not to patients with thal.m and thal intermedia. The reasons for this observation are still unclear. This similarity could be related in part to the relativly low number of transfusions, starting later in life, of patients with homozygous SCD or sickle/β- thal. compared to patients with thal.m. (1) The liver is the dominant iron storage organ and iron liver concentration correlates closely with the total body iron content. While iron uptake by hepatocytes is predominately mediated via transferrin and correlates with serum ferritin levels, as confirmed in the present study, this is not the case in regulation of cardiac and endocrine iron uptake. These organs might acquire the excess metal differently. It is possible that additional and/or different forms of iron, which have been identified, such as non-transferrin bound iron and labile plasma iron, are involved in determining iron loading in the heart and endocrine glands and/or because regulation of iron entry into the plasma by hepcidin might differ. Additional studies are in progress to address these issues.