Progression of Central Nervous System Vasculopathy in Young Adults with Sickle Cell Anemia

Introduction

Silent cerebral infarcts (SCI) and cerebral vessel stenosis are common and progressive in sickle cell anemia (SCA). Most data regarding brain lesions in SCA are cross-sectional or derive from pediatric cohorts with short follow-up not spanning the transition into adulthood. While hydroxyurea and transfusions may reduce the incidence of SCI and abnormal transcranial Doppler (TCD) in children with SCA, data on the effectiveness of these therapies in young adults are lacking. We tested the hypothesis that SCI and cerebral vessel stenosis progressed in young adults with SCA, relative to their childhood years. In addition, we explored the relationship between progression of brain vasculopathy and exposure to disease-modifying therapy.

Methods

We obtained brain magnetic resonance imaging (MRI) and MR angiography (MRA) in adults with SCA (HbSS or HbSβ⁰-thalassemia) on chronic transfusions or hydroxyurea. Participants were recruited from the IRB-approved longitudinal cohort study, Sickle Cell Clinical Research and Intervention Program (Hankins et al., PBC 2018). Participants were ages 18.0 to 32.0 at adult imaging and had at least one prior MRI/MRA between 0 and 17.9 years. Pediatric MRI/MRAs were performed for clinical indications (e.g., neurologic concern). All pediatric and adult MRI/MRAs had similar imaging protocols and were centrally reviewed by a neuroradiologist. SCIs were defined as focal T2-weighted or FLAIR hyperintensity. MRIs were considered abnormal if SCI or overt strokes were present. MRI progression was defined as new SCI or new overt strokes. Vessel stenoses were graded using a validated vasculopathy scale from 0 to 6 (Helton et al., Blood 2014). Abnormal MRA was defined as a score ≥1 and progression as any increase in the vasculopathy grading. We retrospectively ascertained childhood TCDs, treatments, overt strokes, and transient ischemic attacks (TIA, <24 hours neurologic symptoms with no imaging change). The proportion of abnormal brain MRI/MRA was calculated for the participants' pediatric (0-11.9), adolescent (12.0-17.9), and young adult (18.0-32.0) years and compared using multivariate generalized linear mixed model. Multivariate logistic regression investigated the association of exposure to hydroxyurea or chronic transfusion with MRI/MRA progression from child to adulthood.

Results

Forty-one young adults with SCA, all African American, median age 19.0 years, (range 18.0-31.5) were included (Table 1). All received disease-modifying therapy prior to adult MRI/MRA; median duration of hydroxyurea was 10.4 years (range, 0.3 to 20.35) and chronic transfusion was 9.2 years (range, 2.5 to 14.6). Indications for chronic transfusion were: abnormal TCD (N=6), overt stroke (N=4), recurrent vaso-occlusive events (VOE) (N=1), and chronic kidney disease (N=1). Indications for hydroxyurea were: VOE (N=27), overt stroke (N=1), and abnormal TCD (N=1). The total follow-up time from pediatric to adult brain MRI/MRA was 804 person-years, during which 2 patients had new strokes and 5 had TIAs. Progression of MRI and MRA occurred in 12 (29%) and 8 (20%) young adults, respectively, in relation to their pediatric exams (p=0.04 and p=0.01), both among hydroxyurea (Figure 1a) and transfusion (Figure 1b) groups. Both MRI and MRA progression occurred more frequently among those with prior stroke or conditional or abnormal TCD velocities, p=0.015. Controlling for age at adult imaging, exposure to hydroxyurea was associated with decreased probability of MRI progression (OR=0.05, 95%CI: 0.01~0.52, p=0.01), but not MRA (OR=0.22, 95%CI: 0.02~2.34, p=0.2). When further adjusting for transfusions, exposure to hydroxyurea was still associated with decreased probability of MRI progression (OR=0.05, 95%CI: 0.4~0.64, p=0.021) but not transfusions (OR 0.94, 95%CI: 0.16~5.39, p=0.95).

Conclusion

Close to a quarter of young adults with SCA treated with disease-modifying therapies for approximately a decade, experienced progression of brain lesions despite treatment with disease-modifying therapies. Among patients exposed to hydroxyurea, less progression of SCIs occurred. Overt stroke or TCD elevation in childhood increased the risk of brain lesion progression. In children with SCA, the presence of SCI and vessel stenosis in childhood should prompt consideration of alternative treatments given the evidence that brain lesions progress as they emerge into adulthood.

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