Study Finds Link Between Alzheimer's, Bipolar Disorder, and HCV

There is an association of Alzheimer’s disease (AD) in bipolar disorder (BD) patients previously infected with hepatitis C virus (HCV), according to a recent study.

Led by researchers from the School of Health Care Administration at Taipei Medical University in Taiwan, the study found that BD patients diagnosed with HCV were about twice as likely to have also been diagnosed with AD.

An underlying reason for this pattern may be in BD’s commonality as a mental disorder, and its noted tendency to result in dementia among older patients, researchers noted. At the same time, researchers pointed to studies that indicate BD patients have an increased risk of infectious disease due to higher-risk behaviors. HCV infection is reported in 10% to 23.3% of BD patients — a “remarkably elevated risk” compared to the general population’s rate of 1.8%, researchers wrote.

The case-control study used data from 2000-2013 from the Taiwan Longitudinal Health Insurance Database, which includes claims data for about 1 million beneficiaries under the Taiwan National Health Insurance (NHI) program. The database has logged enrollee’s healthcare information since 1995.

Researchers identified 9,239 patients at least 18 years old to have been treated for BD in the span of the studied 13 years. Of that total, 73 patients were also diagnosed with AD — aged between 58-79 years old. Study cases were restricted to patients who had received acetylcho-linesterase inhibitor treatment.

Researchers randomly selected 365 control BD subjects from the pool of patients without an AD diagnosis. The control patients were matched on age, sex, and index year (year of corresponding case’s first recorded AD diagnosis).

Among the 438 total BD patients researched, 83 (18.95%) had been diagnosed with HCV. In BD patients also diagnosed with AD, the HCV rate was 31.51%. In BD patients not diagnosed with AD, the HCV rate was 16.44%.

BD patients with AD reported a 2.3-fold increased risk of prior HCV infections, when adjusted for demographic factors, according to the study.

This was the first epidemiological study in medical literature to distinguish an association between prior HCV infection and AD within BD patients, researchers wrote, though studies have shown a link between HCV and cognitive impairment is “independent of symptom severity, history of substance abuse, and other neuropsychiatric manifestations.”

However, researchers also noted that, in a population-based cohort study, HCV was identified as an independent risk factor for AD.

“It is plausible that this link may be particularly salient for patients with BD, a high-risk population for both HCV infection and dementia, especially AD,” researchers wrote.

HCV is also capable of directly affecting the central nervous system (CNS) and causing brain dysfunction, researchers noted.

“Studies indicate that HCV in the CNS elicits neuroinflammation, with specific cytokines shown to change neuroendocrine and neurochemical pathways that are associated with cognitive function,” researchers wrote. “Patients with HCV infection are also found to have abnormal cerebral glucose metabolism and neurotransmission, another mechanism to explain the functional deficits.”

There is no information from the database that specified patients’ HCV genotype diagnoses, though the most prevalent HCV genotypes in Taiwan are 1b and 2a, according to the study. Cognitive impairment is perceived to affect both of these HCV genotype patients.

Researchers proposed the association among conditions may also be correlated to poverty, poor social environment, or poor health and behaviors in BD patients. They called for appropriate surveillance and early recognition of AD among BD patients to have had HCV infections.

“Our study finding of considerably high risk of AD among BD patients who were also chronic carriers of HCV supports alerting psychiatrists and gastroenterologists and family care-givers to identify early AD symptoms among these patients,” researchers wroter. “Furthermore, despite the higher risk of patients with BD for HCV infection, there is a lack of awareness about HCV among providers due to fragmentation of care and the disadvantages faced by patients with severe mental illness.”

Further research into underlying pathophysiological mechanisms, as well as the role of BD, should follow, according to the study. High-risk psychiatric populations would benefit from studies on the effects of appropriate HCV treatment among BD patients.

The study, "Association of Alzheimer's disease with hepatitis C among patients with bipolar disorder," was published on the online journal PLOS ONE on June 16, 2017.

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