The autoimmune thyroid disease Hashimoto’s thyroiditis, also known as hypothyroidism, is diagnosed in people with RA more than in the general population, says Andrew Wang, MD, PhD, a rheumatologist at Yale Medicine and assistant professor of immunology at the Yale School of Medicine in New Haven, Connecticut. And Graves’ disease, which causes hyperthyroidism, can also co-occur in people with RA. In many people, the RA is diagnosed first, but that doesn’t mean it always starts earlier, Dr. Wang says. It is often difficult to know which came first, he says, because thyroid symptoms, as with early RA symptoms, includes tiredness, body aches, and other nonspecific signs. Once a person develops joint pain, though, the RA might be diagnosed. Only then do some doctors think to test for thyroid problems, Wang says.
There May Be a Genetic Link Between RA and Thyroid Disease
Hashimoto’s occurs when the immune system mistakenly attacks thyroid cells, interfering with their ability to make thyroid hormone. Exactly how the two conditions are linked is not yet fully understood, but shared genes may play a role in susceptibility to autoimmune diseases. Genetically induced autoantibodies are common in people with RA, and autoantibodies also mediate autoimmune thyroid disease, Wang says. “The same pathway controlled by each of these diseases can lead to pathways for other autoimmune diseases,” he says. Eric L. Matteson, MD, emeritas professor of rheumatology at Mayo Clinic in Rochester, Minnesota, says heart disease is also more prevalent among individuals with both hypothyroidism and RA. “It’s the trifecta,” said Dr. Matteson. “When you have an underactive thyroid, it can make you feel quite tired, just like RA. Everyone assumes it is the RA, so nobody thinks to look for alternate causes.” A study by Danish researchers, published in the journal Medicine in October 2017, similarly documented the co-occurrence. In this study of 439 people with newly diagnosed RA, the prevalence of thyroid disorders in these people was found to be 16 percent, with hypothyroidism the most frequent.
Blood Work Is Important for Thyroid Diagnosis
“If someone with RA has unusual new fatigue that is getting worse and weight gain, these symptoms should make us think that their thyroid is not functioning properly, and it’s reasonable to check thyroid function with blood tests,” Matteson says. Sometimes, thyroid issues are accidentally uncovered. “Someone may have RA and be treated, and then their rheumatologist may do blood work and find an underactive thyroid," Matteson says. Alternatively, sometimes a person has hypothyroidism and develop worsening joint pain, and they may subsequently be diagnosed with RA. Blood tests for thyroid function levels of thyroid stimulating hormone (TSH) as well as Free T4 are the best way to diagnose thyroid issues, Wang says. People with RA whose rheumatologist ignores complaints of nonspecific symptoms like fatigue and fogginess because blood markers show there is good control of RA should be pushy, he says. “I would advocate having the doctor test the thyroid in this situation,” he says. Testing is also important because other issues can cause problems with the thyroid that are even more serious, including thyroid cancer, he says.
There Are Good Treatments for Thyroid Disease and for RA
The good news: Hypothyroidism can be treated relatively easily with synthetic thyroid medication. Hyperthyroidism is a bit more challenging, but treatments are available for this condition as well. Often a rheumatologist will prescribe the thyroid medicine, or they may refer the person to an endocrinologist, Wang says. Also reassuring: Thyroid medication won’t interfere with rheumatoid arthritis medication, so both conditions can be treated simultaneously and successfully, Matteson says. Diagnosing thyroid disorders at the earliest stage is always ideal, doctors say. Doing so may also be important for a person’s RA as well. The Medicine study found that RA patients with thyroid disorders had significantly poorer initial response to RA treatment after four months, compared with patients without thyroid issues, leading researchers to conclude that the presence of thyroid disorders in RA patients suggests a more aggressive rheumatoid disease.
Similar Symptoms
Some overlapping symptoms include swelling around the feet and legs, muscle discomfort, and weight gain. “If someone with RA has unusual new fatigue that is getting worse and weight gain, these symptoms and signs should make us think that their thyroid is not functioning properly, and it’s reasonable to check thyroid function with blood tests,” he says. The reassuring news: thyroid medication won’t interfere with rheumatoid arthritis medication, so both conditions can be treated simultaneously and successfully, he adds. The diseases can emerge in any order or happen simultaneously, says Matteson. “Someone may have RA and be treated, and then their rheumatologist may do blood work and find an underactive thyroid," he notes. Or someone may have hypothyroidism and develop worsening joint pain, and they may subsequently get diagnosed with RA. Often, blood tests are the only way to figure out which condition is driving the symptoms. But, cautions Matteson, most people with hypothyroidism don’t have RA. “We don’t routinely screen for RA in the absence of symptoms,” he said.
