Extension Study of BIIB092 in Participants With Progressive Supranuclear Palsy (PSP) Who Participated in CN002003

Key Inclusion Criteria: 1. Completed treatment in Study CN002003. 2. A diagnosis of probable or possible PSP consistent with Study CN002003 criteria with no new medical information or diagnoses since enrollment into Study CN002003 that might confer doubt on the PSP diagnosis. 3. Able to tolerate Magnetic Resonance Imaging (MRI). 4. Able to perform all protocol-specified assessments and comply with the study visit schedule. 5. Have reliable caregiver to accompany patient to all study visits. Caregiver must be able to read, understand, and speak local language fluently to ensure comprehension of informed consent and informant-based assessments of patient. Caregiver must also have frequent contact with patient (at least 3 hours per week at one time or at different times) and be willing to monitor the patient's health and concomitant medications throughout the study. 6. Patient must reside outside a skilled nursing facility or dementia care facility at the time of enrollment 7. Women of childbearing potential (WOCBP) and sexually active fertile men with partners who are WOCBP must use highly effective birth control. Key Exclusion Criteria: 1. Presence of an unstable, clinically significant medical condition other than PSP including, but not limited to: hematological, endocrine, cardiovascular, renal, hepatic, gastrointestinal, immunological, psychological or neurological disease or malignancy. 2. Contraindication to undergoing a lumbar puncture (LP). 3. Recent drug or alcohol abuse as defined in Diagnostic and Statistical Manual of Mental Disorders (4th Edition). 4. Treatment with any investigational drugs (including placebo) other than BIIB092 or placebo given in Study CN002003 or devices within 90 days prior to enrollment 5. Any vaccination within 30 days prior to study drug administration. 6. Contraindication to the MRI examination for any reason 7. Any other sound medical, psychiatric, and/or social reason as determined by the investigator 8. Known history of human immunodeficiency virus. 9. Evidence of organ dysfunction or significant deterioration from prior values in CN002003 beyond what is consistent with the target population or that would place the patient at increased risk or risk of early study discontinuation. 10. Inability to be venipunctured and/or tolerate venous access. 11. History of allergy, hypersensitivity, or serious adverse reaction to monoclonal antibodies or related compounds or allergy to any of the components of the study drug NOTE: Other protocol defined Inclusion/Exclusion criteria may apply