Discussion:
This study represents, to our knowledge, the largest retrospective
cohort of pediatric patients with SCD-MMS analyzing the effectiveness
and safety of surgical revascularization compared to conservative
therapy. After initiation of treatment, no strokes were observed in the
ten patients who underwent surgical revascularization, while three of
the seven patients who underwent conservative therapy experienced a
stroke during the course of the average 7.4 year follow-up despite
having less severe cerebral vasculopathy. No significant complications
of surgery were observed.
Hankinson et al. examined 12 pediatric SCD-MMS patients who underwent
surgical revascularization for an average of 46.8 months follow-up and
found no strokes post-operatively and no major surgical
complications.9 Only four of the patients were
compliant with CTT protocol throughout the study; patients who received
conservative treatment only were not included. Greissenhauer et al.
examined a similar cohort of 14 pediatric SCD-MMS patients on CTT who
underwent surgical revascularization.7 There was one
observed stroke in the cohort and a reported 5-fold reduction risk in
stroke compared to pre-surgical risk. Our group recently published a
systematic review of the literature available on surgical
revascularization for children with sickle cell disease and moyamoya
syndrome. We found an overall rate of ischemic stroke free survival of
94.3% with only 1.8% intraprocedural complications.2
A study comparing conservative and surgical treatment was published by
Yang et al. who examined 15 pediatric SCD-MMS
patients.17 Seven patients underwent surgical
revascularization and eight patients underwent conservative therapy. The
authors observed no strokes in the surgical revascularization group and
four strokes in the conservative treatment group with an average
follow-up of 11.6 years equating to a 2.3% risk of stroke per year. The
results of our study showed very similar results to these studies. We
observed a stroke risk of 3.0% per year in SCD-MMS patients undergoing
conservative therapy alone and no risk of stroke in patients who
underwent surgical revascularization. When considering the differences
in average vasculopathy scores and observing a statistically significant
difference between the two groups, the evidence of more severe
vasculopathy in the surgical group supports the protective nature of the
surgery treatment in regards to stroke.
Although our study does not show a statistically significant difference
between treatment options, there is a clear trend towards a clinically
significant reduction of stroke risk associated with surgical
revascularization. By combining our data with published data from the
Yang et al. study17 and the Hall et al.
study8 (the only studies with similar cohorts of
patients and detailed outcomes), the pooled data showed a statistically
significant difference (p=0.001) in the stroke rates between the
conservative (n=30) and surgical (n=29) groups. Figure 4 shows the
difference in survival curves with the surgical group showing superior
results.
The major limitations of our study are the lack of statistical power due
to small sample size and the lack of equivalent long-term follow-up in
the surgical revascularization group. Furthermore, the two treatment
groups are not likely to differ only in the surgical therapy due to the
retrospective design of the study. A multi-center, retrospective study
is currently underway to accrue a larger patient sample in order to
better detect a difference in stroke outcome between conservative
treatment and surgical revascularization.