published in JAMA Internal Medicine.
The study found that these patients with thyrotoxicosis had a higher likelihood of incident cognitive disorder (adjusted hazard ratio, 1.39; 95% confidence interval, 1.18-1.64; P < .001). Broken down between internal and external causes of thyrotoxicosis, exogenous thyrotoxicosis continued to be a significant risk factor (aHR, 1.34: 95% CI, 1.10-1.63; P = .003), while endogenous thyrotoxicosis did not show a statistically significant risk estimates (aHR, 1.38; 95% CI, 0.96-1.98; P = .08).
The study also found that women were more likely to have low levels of thyrotropin (thyroid-stimulating hormone/TSH) than men and were more likely to be overtreated.
Previous studies looking at the correlation between hyperthyroidism and cognitive disorders often did not include participants who were already taking thyroid hormones, according to Jennifer S. Mammen, MD, PhD, assistant professor of medicine at the Asthma and Allergy Center at John Hopkins University, Baltimore, and the senior author of the study.
“The fact that we see the signal both in people who are being overtreated with thyroid hormone and in people who have endogenous hyperthyroidism is one way that we think that this supports the fact that it’s not just confounding, it’s not just bias,” Dr. Mammen said. “There’s two different sources of hyperthyroidism, and they’re both showing the same relationship.”
In the study, Dr. Mammen and colleagues analyzed electronic health records for patients aged 65 years and older who received primary care in the Johns Hopkins Community Physicians Network over a 10-year period starting in 2014. Patients had to have a minimum of two visits 30 days apart. None had a history of low TSH levels or cognitive disorder diagnoses within 6 months of their first doctor visit.
More than 65,000 patients were included in the study. Slightly more than half (56%) were female, almost 70% were White, 19.3% were Black, 4.6% were Asian, and 0.4% were American Indian. Almost 25,000 low TSH measurements among 2,710 patients were recorded during the study period. The majority of low TSH measurements were exogenous (14,875), followed by origins of unknown cause (5,833), and endogenous (4,159).
During the follow-up period, 7.2% (4,779) patients received a new cognitive disorder diagnosis, which was dementia in 77% of cases.
Dr. Mammen said primary care physicians should carefully consider whether thyroid hormone therapy is necessary for older patients, and, if so, great care should be taken to avoid overtreatment.
“This is yet another reason for us to be vigilant about not overtreating people with thyroid hormone, especially in older adults,” Dr. Mammen said. “We already know that atrial fibrillation rates are increased in people who are hyperthyroid. We know that fracture and osteoporosis is affected by hyperthyroidism. And now we also have an association with higher rates of cognitive disorders.”
Taking a cautious approach to prescribing thyroid hormone therapy for older patients is paramount, according to Jean Chen, MD, partner at Texas Diabetes & Endocrinology, who was not affiliated with the study.
“All medical providers need to be aware that the 65 and older population does not need to be treated as aggressively with their thyroid hormone,” Dr. Chen said. “We are finding more and more complications from overtreatment rather than benefit in this population.”
Often, older patients may complain of symptoms such as constipation, feeling cold, or tiredness, which can be symptoms of hypothyroidism. But these symptoms could also be from anemia, vitamin deficiencies, depression, perimenopause, menopause, insulin resistance, and sleep apnea. If necessary, Dr. Chen recommended primary care physicians consult with an endocrinologist regarding a possible treatment plan and making a differential diagnosis.
In addition, Dr. Chen said other studies have shown that treating patients with thyroid hormone either did not resolve the condition or negatively impacted anxiety, muscle strength, and bone density, or it increased the risk for arrhythmia. Therefore, it’s important to weight the risks versus the benefits.
“There’s so much gray zone here,” Dr. Chen said.
The study was supported by the Richman Family Precision Medicine Center of Excellence in Alzheimer’s Disease, the Richman Family Foundation, the Rick Sharp Alzheimer’s Foundation, the Sharp Family Foundation, among others. The work was also supported by grants from the National Institutes of Health. One coauthor reported personal fees from Karuna, MapLight Therapeutics, Axsome Therapeutics, GIA, GW Research Limited, Merck, EXCIVA, Otsuka, IntraCellular Therapies, and Medesis Pharma for consulting for treatment development in Alzheimer’s disease outside the submitted work. No other disclosures were reported.
A version of this article appeared on Medscape.com.