A positive ACR50 response is defined if the following 3 criteria for improvement from baseline were met: * 50% improvement in 68 tender joint count; * 50% improvement in 66 swollen joint count; and * 50% improvement in at least 3 of the 5 following parameters: * Patient's assessment of joint pain (measured on a 100 mm visual analog scale \[VAS\]), * Patient's global assessment of disease activity (measured on a 0-10 Likert scale), * Physician's global assessment of disease activity (measured on a 0-10 Likert scale), * Patient's self assessment of disability (Health Assessment Questionnaire - Disability Index \[HAQ-DI\]), * Acute phase reactant: erythrocyte sedimentation rate (ESR) or C-Reactive Protein (CRP), whichever has bigger improvement.

An adverse event (AE) is any untoward medical occurrence in a participant administered a pharmaceutical product and that does not necessarily have a causal relationship with this treatment, including any such occurrence (eg, sign, symptom, or diagnosis) or worsening of a pre-existing medical condition. A serious adverse event was defined as an adverse event that was fatal; was life threatening; required in-patient hospitalization or prolongation of existing hospitalization; resulted in persistent or significant disability/incapacity; was a congenital anomaly/birth defect; or other significant medical hazard.

The investigator reviewed laboratory test results and determined whether an abnormal value in an individual study participant represented a change from prestudy values and determined if changes were clinically significant. The number of participants with clinically significant changes in lab values at any time during the study is reported.

Samples were tested in a validated immunoassay for the presence of anti-brodalumab binding antibodies. Samples found to be positive for binding antibodies were further tested using a validated cell-based bioassay to determine if the antibodies were able to neutralize the activity of brodalumab.