It’s well established that inflammatory types of arthritis, like rheumatoid arthritis, or RA, are associated with an increased risk of cardiovascular disease. Now, a Dutch study shows that if in addition to the arthritis you have hypothyroidism – a condition in which the thyroid gland produces an insufficient amount of hormones – your risk is even higher.

“Evidence is accumulating,” explains study co-author Michael T. Nurmohamed, MD, PhD, a rheumatologist at VU University Medical Center in Amsterdam. “Rheumatoid arthritis as well as hypothyroidism are independently associated with an increased cardiovascular risk, such as heart attacks and strokes. If you have both, then the risk is amplified,” he says. The study was published online March, 2012, in Annals of the Rheumatic Diseases.

For the study, the researchers collected information from a primary care database on more than 175,000 Dutch patients older than 30. They used diagnosis codes to identify patients with inflammatory types of arthritis – defined in this study as RA and ankylosing spondylitis, a type of arthritis that primarily affects the spine and pelvis – as well as those with hypothyroidism and cardiovascular disease, or CVD, including heart attack and stroke.

More than 1,500 patients were found to have inflammatory arthritis. Both male and female patients with inflammatory arthritis had higher rates of hypothyroidism than those without inflammatory arthritis – 6.5 percent vs. 3.9 percent among women, and 2.4 percent vs. 0.8 percent among men. 

After adjusting for risk factors including age, hypertension, cholesterol levels and the presence of diabetes, researchers found female patients with both inflammatory arthritis and hypothyroidism had a 3.7 times higher prevalence of cardiovascular disease than the control group (people without either condition). Female patients with only inflammatory arthritis had a 1.5 higher prevalence of CVD compared to controls and those with hypothyroidism had a 1.2 percent higher prevalence of CVD. There weren’t enough male patients with both conditions to conduct a meaningful analysis.

Dr. Nurmohamed and his colleagues write that a link between inflammatory arthritis and hypothyroidism has long been suspected, but evidence scientifically supporting the association was lacking. Inflammatory types of arthritis are autoimmune disorders, in which the body attacks itself. The most common cause of hypothyroidism is another autoimmune disorder, called Hashimoto’s disease, in which the body attacks its own thyroid gland.
 

“If you have one autoimmune disorder, you have a higher chance, in comparison to the general population, to develop another autoimmune disorder,” says Dr. Nurmohamed. “The underlying cause might be from genetic origin,” he explains, as well as environmental risk factors.

Mala S. Kaul, MD, a practicing rheumatologist and assistant professor of medicine in the division of rheumatology at Duke University, in Durham, N.C., says this study isn’t likely to change clinical practice. “The fact that they have inflammatory arthritis already should be alerting the rheumatologist and primary care doctor that they have a fairly well-established risk for cardiovascular disease,” Dr. Kaul explains.

Eric Ruderman, MD, a practicing rheumatologist and professor of medicine at Northwestern University’s Feinberg School of Medicine, in Chicago, points out that this study doesn’t explain why there is an increased risk or if it would decrease if the hypothyroidism is well managed. But he believes the new data are significant. 

“Here is yet another risk factor that appears to be pretty important. So it may mean in people with RA and a history of cardiovascular disease that it makes sense to check their thyroid status, because it's another risk you could [mitigate],” Dr. Ruderman explains. “If you follow all these things, can it have an impact? It may or may not. In the meantime, though, checking someone's thyroid status with a blood test is a benign thing.”

Since a primary care doctor or an endocrinologist generally monitors hypothyroidism, Dr. Ruderman and Dr. Kaul agree it may be challenging to figure out which of your doctors should take the lead in monitoring this increased risk.

“That's the challenge. Whose job is this? I think it's everybody's job,” Dr. Ruderman says. “In the end, whoever makes note of the issue is doing the patient a favor.” The message to patients: If you have inflammatory arthritis, see if you need to be tested for hypothyroidism, and make sure you know which doctor is monitoring your conditions.