OBJECTIVE: This study was designed to identify predictive factors associated with substantial contralateral progression in adult patients with bilateral nonhemorrhagic moyamoya disease (MMD) who undergo revascularization surgery (RS) on one hemisphere. METHODS: The authors retrospectively analyzed 174 contralateral hemispheres of patients with bilateral nonhemorrhagic MMD (non-hMMD) who underwent RS on one side. The primary endpoint was defined as substantial contralateral progression requiring additional RS 6 months after the initial RS. The annual risk and predictive factors for contralateral progression were also analyzed. RESULTS: Of 174 patients included in the study, 57 (32.8%) experienced contralateral progression over a mean follow-up of 45.3 ± 31.6 months (range 12-196 months). The annual risk for contralateral progression after initial unilateral RS was 7.7% per person-year. Multivariable analysis revealed that age (HR 0.967, 95% CI 0.944-0.992
p = 0.009) and a BMI ≥ 25 (HR 1.946, 95% CI 1.126-3.362
p = 0.017) were significant predictors of contralateral progression. Specifically, the annual risk of contralateral progression was 12.1% in the higher BMI (≥ 25) group and 4.0% in the lower BMI (<
25) group per person-year. CONCLUSIONS: The study revealed a 7.7% per person-year rate of contralateral progression in patients with bilateral non-hMMD following unilateral RS. Younger age and a BMI ≥ 25 were identified as significant risk factors. For these patients, careful weight management and the use of antilipid agents may be crucial strategies for reducing the risk of contralateral progression after unilateral RS.