An AE is any untoward medical occurrence in a participant/clinical investigation participant administered a pharmaceutical product and that does not necessarily have a causal relationship with this treatment. An AE can be any unfavorable and unintended sign (including an abnormal laboratory finding), symptom, or disease temporally associated with use of medicinal(investigational) product, whether or not related to medicinal (investigational) product. An SAE is any untoward medical occurrence that at any dose results in death, is a life-threatening event, requires inpatient hospitalization or prolongation of existing hospitalization, results in significant disability/incapacity or congenital anomaly, is medically important event. TEAE or Serious TEAEs are defined as any AE that has an onset date and time that is on or after date and time of first dose of study treatment, or that has worsened after date and time of first dose of study treatment.

The safety population for the core period included all participants who had received at least one dose of aducanumab in the core period.

An AE is any untoward medical occurrence in a participant or clinical investigation participant administered a pharmaceutical product and that does not necessarily have a causal relationship with this treatment. An AE can therefore be any unfavorable and unintended sign (including an abnormal laboratory finding), symptom, or disease temporally associated with the use of a medicinal (investigational) product, whether or not related to the medicinal (investigational) product.

The safety population for the core period included all participants who had received at least one dose of aducanumab in the core period.

Number of participants diagnosed with ARIA edema are reported.

The safety magnetic resonance imaging (MRI) population for the core period included all participants who had received at least one dose of aducanumab in the core period and had at least one post-baseline MRI assessment in the core period. Here, 'overall number of participants analyzed' signifies the number of participants with data available for outcome measure analysis.

Number of participants diagnosed with ARIA hemmorrhage or superficial siderosis are reported.

The safety MRI population for the core period included all participants who had received at least one dose of aducanumab in the core period and had at least one post-baseline MRI assessment in the core period. Here, 'overall number of participants analyzed' signifies the number of participants with data available for outcome measure analysis.

The presence of serum ADAs was determined using a validated assay. A standard 3-tiered approach was used including screening assay, confirmatory assay, and titration assay. The number of participants with a positive response to ADAs are reported.

The immunogenicity population for the core period included all participants who had received at least one dose of aducanumab in the core period and had at least one post-dose sample evaluated for immunogenicity in the core period. Here, 'overall number of participants analyzed' signifies the number of participants with data available for outcome measure analysis.