Psoriatic Arthritis and Thyroid Disease Can Appear Together
The link between the two may not be as strong as for other autoimmune conditions like rheumatoid arthritis, but that may be because the research is not as robust.
Psoriatic arthritis (PsA)?is an inflammatory arthritis of the joints that occurs in some people who have?psoriasis. Both PsA and psoriasis are autoimmune diseases, meaning they are caused by a person’s own immune system going astray. It’s long been known that people who have one autoimmune condition are more prone to developing others.
It’s not surprising, then, that some people with PsA also develop an autoimmune thyroid disorder.
Problems With the Thyroid
The thyroid is a butterfly-shaped gland at the base of the throat. For such a small part of the body, it can wreak a lot of havoc. This is because the thyroid has many?crucial functions, including regulating heartbeats and controlling how speedy or sluggish your metabolism is.
Even among the general population, thyroid disease is not rare. According to the?American Thyroid Association (ATA), an estimated 20 million Americans have a thyroid condition. But because symptoms can be nonspecific and hard to attribute directly to the thyroid, up to 60 percent of people are unaware they have it, the ATA says.
Like other glands, the thyroid excretes hormones into the body. When it pumps out too little (hypothyroidism) or too much (hyperthyroidism), a person can feel tired or amped up and may gain or lose weight. Other common symptoms of thyroid problems include depression, constipation, and difficulty concentrating from too little of the hormones, and nervousness, palpitations, and insomnia from too much.
PsA Is Linked to Thyroid Function, but Not as Strongly as Other Conditions
With some autoimmune diseases, such as rheumatoid arthritis, people develop autoantibodies, which mistakenly target the person’s own tissue, as part of the disease. But those with psoriatic arthritis do not develop these autoantibodies, says Andrew Wang, MD, PhD, a rheumatologist at Yale Medicine and an assistant professor of immunology at the Yale School of Medicine in New Haven, Connecticut.
It's more common for people with autoantibody diseases to also develop autoimmune thyroiditis than it is for those with conditions that don’t make autoantibodies, Dr. Wang explains. This means that the co-occurrence rate between autoimmune thyroid disease and PsA is not as high as for other autoimmune diseases, like RA, he says.
Psoriasis and Autoimmune Thyroid Disease Are Linked
Nonetheless, even among people with psoriasis, whether or not they also have PsA, rates of thyroid disease are higher than in the general population. A meta-analysis by Chinese researchers published in BMJ Open in January 2022 found that people with psoriasis have a higher prevalence of autoimmune thyroid disease, most commonly hypothyroidism.
Few Studies Exist on PsA and Thyroid Disorders
Very few studies have examined the rate of thyroid disease specifically in people with PsA. In a review of the two diseases published in Cureus in January 2021, California researchers found just 45 high-quality articles on the topic.
Most of the studies they examined do show a positive association, meaning if someone has one condition they were more likely than the general public to have the other. But six of the studies showed no increased connection.
The researchers found that the coupling was more common in people who are obese. In some studies, young women were also more prone, but in other research this wasn’t the case. People who developed psoriasis in midlife or later, known as late-onset disease, were also more likely to have a thyroid condition than those with early onset.
Because of the small number of studies, though, the researchers could not provide a concrete explanation for the concurrence of the two conditions. “More prospective and retrospective studies are needed to assess the association between them before any conclusion can be made,” they wrote.
Medications Don’t Interfere — and May Even Help
The good news is that regardless of what medications a person is taking to control their psoriatic arthritis, they can continue on them while undergoing treatment for any thyroid condition, Dr. Wang says. “Among all the drugs, none of them would affect psoriatic arthritis treatment,” he says.
Intriguingly, the Cureus review found hints that some thyroid treatments may actually improve PsA symptoms. For example, the drug propylthiouracil, which is used to treat hyperthyroidism, was found in several studies to clear psoriatic lesions. And two studies noted that after a thyroidectomy (a surgical procedure for hyperthyroidism that removes part of the thyroid), there was marked improvement in psoriatic skin lesions.
Be Sure Your Doctor Takes Thyroid Symptoms Seriously
Because symptoms of thyroid disease may be vague, doctors don’t always think to check the thyroid when PsA patients complain of things like fatigue, insomnia, or weight gain, Wang says.
“It’s important for people with psoriatic arthritis to make sure your doctor is listening to you,” he says. If you’re experiencing new or unusual symptoms, “I would advocate that your doctor consider the thyroid,” he says. A simple blood test checking for thyroid hormone levels can reveal whether that’s the source of the problem.