Cardiac Iron Overload in Sickle Cell Disease: When to Screen and How to Intervene

Background

Iron overload is a recognized consequence of chronic transfusion therapy in patients with sickle cell disease (SCD), but most of the focus to date has been on the effects of increased liver iron concentration (LIC) with increasing transfusion burden. Even though there is a robust body of literature concerning cardiac iron overload (CIO) in patients with thalassemia major, there remains a paucity of data in how to detect and treat CIO in patients with SCD, particularly in the pediatric and young adult population. While CIO is seen less commonly in sickle cell disease than in thalassemia, patients with SCD remain at risk, with recent studies demonstrating an incidence of 2-5% of CIO in chronically transfused patients with SCD. We performed a retrospective chart review of patients with cardiac MRIs (cMRIs) and LICs by Ferriscan performed at our institution to identify risk factors for CIO, as well as to characterize institutional practice for assessing cardiac iron in the absence of defined practice guidelines.

Methods

We reviewed clinical characteristics of all patients with SCD who had cMRIs performed at Children's Healthcare of Atlanta between June 2012 and December 2017. We then queried our institutional sickle cell database for patients who were at least 3 years old in 2010, genotype SS or S Beta zero thalassemia, were on chronic transfusions for at least 5 years by 2017, and had not undergone a cMRI. Patients who were status post bone marrow transplant were excluded. For comparison of age, average ferritin, and transfusion duration, significance among means between patients with and without CIO was calculated using a two-tailed unpaired t-test. For comparison of LIC, significance among medians was calculated using the Mann Whitney test. A p value of <0.05 was considered significant. Statistical analyses were performed using Prism 6 (GraphPad Software, Inc.).

Results

Of 36 evaluable patients who had undergone cMRI, there were 11 with CIO, as defined by a T2* < 20ms. Clinical characteristics are shown in Figure 1. Patients were 7-28 years of age, and had received chronic transfusion therapy for a range of 22 months to 228 months. Between patients who did and did not have CIO, there was no significant difference in average 1-year ferritin level (6786 vs 6373 ng/mL, p=0.79), transfusion duration (103 vs 123 months, p=0.41), or age (15 vs 18 years, p=0.12). There was a higher median LIC by Ferriscan of > 43 mg/g in those with CIO vs 34 mg/g in those without CIO, although this was not statistically significant (Figure 1). Interestingly, CIO was seen as young as 7 years of age and after as little as 22 months of chronic transfusions, and with concurrent LIC values as low as 8.1 mg/g.

Of the 11 patients with CIO, 6 had follow-up cMRI data available, and all 6 had normalization of cardiac iron (T2* > 20ms) on subsequent MRIs (Figure 2 and Table 2). There was 1 patient who did not have full transfusion and chelation history available for analysis. Of the remaining 5, 5/5 had increased or more aggressive chelation added, including 2 who were started on high-dose IV Desferal every 2 weeks; 3/5 also had partial manual exchange (PME) added to their chronic transfusion regimens.

There were 80 patients who were on chronic transfusions but did not have a cMRI performed; as a group, they had a median LIC of 17 mg/g (range: 1.7 - >43 mg/g), an average 1-year ferritin of 3641 ng/mL (range: 520 - 8478 ng/mL), and had been on chronic transfusions for a mean of 87 months at time of Ferriscan study (range: 14 - 192 months). Overall, these patients had a lower transfusion burden than those who received cMRIs, but there were several in this group who had significant iron overload, including 10 who had LIC values of > 43mg/g.

Conclusion

CIO in SCD may be a more salient issue, and occur earlier, than previously described. We did not find a strong relationship between CIO and ferritin levels or LIC by Ferriscan, but we did find that CIO was reversible with more aggressive chelation or the addition of PME. While guidelines for monitoring for CIO in SCD are largely extrapolated from thalassemia data, the rate and physiology of iron loading may be completely different. Due to a paucity of information in this area, more studies are needed to guide screening and to fully assess risk factors that may put certain individuals more at risk for cardiac iron loading.

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