Patients With Older-Age Bipolar Disorder (OABD) Visiting a Memory Clinic: Differentiating Underlying Pathophysiology With MRI and Cerebrospinal Fluid Markers

Background: Many patients with bipolar disorder (BD) report cognitive problems. Pathophysiology of cognitive impairment in BD is unclear, although prevalence of dementia in BD is high. In Older-Age Bipolar Disorder (OABD) patients with cognitive complaints, neurodegeneration may play a role. This could occur in at least 2 ways: (1) BD with ‘comorbid’ diagnosis of dementia; (2) specific neurobiological processes can underlie a cognitive impairment that is intrinsic of BD (ie, BD-related cognitive impairment). Methods: 102 OABD patients were selected from the Amsterdam Dementia Cohort study. Diagnostic workup included clinical and neuropsychological assessment, CSF biomarkers and MRI visual rating scales. About half of patients had depressive symptoms. We (1) examined which neurological diagnoses were identified by the memory clinic as the main cause of cognitive complaints. Subsequently, (2) in the remaining OABD patients with an unknown cause, we performed linear regression between biomarkers of neurodegeneration and composite cognitive score. Results: 29 OABD patients (28.4%) received a neurological diagnosis, 6 of which Alzheimer’s Disease. In the remaining 73 (71.6%) OABD patients, a lower Aβ₄₂CSF concentration was related to lower composite cognitive scores (B = −0.143, P = 0.034), whereas CSF T-Tau, P-Tau, and MRI markers were not. Conclusion: In most OABD patients visiting a memory clinic, a neurological cause of cognitive complaints was not identified despite extensive diagnostic work-up. Altered amyloid metabolism may be an extra biological factor in the multifactorial puzzle that is BD-related cognitive impairment. Future studies should investigate a large range of biomarkers in relation to cognition in BD, including amyloid.