Ankylosing spondylitis (AS) is a form of arthritis. AS is a chronic inflammatory disease that affects your spine and joints, causing pain and limiting range of motion.

It can involve disease flare-ups that cause acute symptoms, followed by remissions in which symptoms ease up.

AS varies a lot from person to person, and from women to men.

The most common symptoms of AS in women include:

  • pain in the spine, lower back, neck, and hips
  • pain in ankles and knees
  • stiffness after rest or sleep
  • fatigue
  • anemia
  • systemic issues, like inflammatory bowel disease and psoriasis

If left undiagnosed and untreated, symptoms can be severe, but not everyone with AS develops spinal fusion or has serious complications.

AS is rare. In the United States, about 0.2 percent of people have been diagnosed with the inflammatory disease. However, research suggests it is still widely underdiagnosed, which may mean AS is more common.

Indeed, some research suggests the number could be closer to 1 percent of the population, or about 3 million people. This puts AS on par with another inflammatory disease, rheumatoid arthritis.

For decades, doctors believed men were significantly more likely to develop AS, but as research has improved, that image has changed dramatically. At one point, men held a 10-to-1 ratio, but with newer research, the male/female ratio has fallen to nearly even.

What’s more, women are more likely to be underdiagnosed and wait longer for a diagnosis. That’s why researchers believe the real prevalence among women may not be fully understood yet.

It takes longer for women to receive an AS diagnosis than it does for men. On average, women wait about 8.8 years for a diagnosis, while men wait 6.5 years, according to a 2017 study.

A combination of factors is responsible for this delay for women. First, how a diagnosis is made can slow down the process for women.

A rheumatologist usually makes the diagnosis of AS. There’s no single test for AS, so reaching that diagnosis may include:

  • individual and family medical history
  • evaluation of symptoms
  • physical examination
  • imaging tests
  • blood work

Imaging tests, like X-rays, are highly valuable for diagnosing AS. That’s because the disease can cause damage to the sacroiliac joint (the joint that connects the hips to the sacrum). This damage is visible on X-rays.

However, some people with the condition will not show obvious signs of damage. This type of AS is called non-radiographic axial spondylarthritis (nr-AxSpA).

It is more common in women than men, and more sensitive imaging with MRI may be needed, which can further delay diagnosis.

The assumption that AS is a predominantly male condition may also delay diagnosis in females.

In addition, studies have generally included many more men than women. Newer studies are addressing this. But much more research is needed to broaden understanding of any gender differences.

AS occurs when the spinal vertebral bodies, and the ligaments and tendons that attach to these bones of the spine, become inflamed. Over time, this swelling causes severe problems within your back.

At first, you may experience frequent back pain or overall stiffness, which may be worse in the morning or after long periods of sitting. You might notice that it improves a bit after a warm shower or a little exercise.

As AS progresses, the pain can become debilitating and cause a reduced range of motion. You might also experience pain in other areas of the body, including the neck, shoulders, elbows, knees, or ankles.

Some people experience only intermittent back pain and discomfort, while others have severe pain and stiffness over multiple areas of the body for long periods of time.

Women have a higher disease burden because of the delay in diagnosis, too.

A 2018 study found that women have higher disease activity, and more damage is likely even if it is not visible. Women are also less responsive to some of the primary treatments for AS.

Women with AS may be at higher risk for depression. A 2014 study found that when compared with the general population, there’s an 80 percent increased rate of depression in women.

Currently, research suggests women are not more likely to have AS than men.

However, AS may be more prevalent in women than once thought, and underdiagnosis could be preventing women from finding the answers and treatments they need.

Indeed, by the time women’s symptoms are identified and the inflammatory disease is diagnosed (typically more than 2 years after men are diagnosed), they have a more advanced disease.

This puts them further behind at the start of treatment.

Age does not affect the severity of the disease, but age is a risk factor.

Arthritis is often considered a disease that comes about with age. But AS commonly occurs in people between ages 17 and 45 years. Some people are diagnosed as early as adolescence.

The age of onset is about the same in men and women. But women may be diagnosed later because of the misconception that AS primarily affects men and because of delays in diagnosing.

Having a family history of the disease increases a person’s chances for developing it. Many people with AS have a gene called HLA-B27. However, having this gene doesn’t mean you’ll develop AS.

Research shows that the prevalence rate of HLA-B27 and developing AS varies among people based on their ethnic background.

For example, about 95 percent of white people who have AS, test positive for the gene.

About 80 percent of people from Mediterranean countries have the condition and the gene, while only about 50 percent of people of African American descent with AS test positive for this gene.

Likewise, in general, people with other inflammatory conditions, like Crohn’s disease, ulcerative colitis, or psoriasis may have an increased risk for developing AS.

It was previously thought that men with AS are more prone to pain in the spine and back than women. Later research indicates that back pain is the main symptom for both men and women seeking diagnosis.

In addition, women may have more neck, hip, and knee pain, while men have more foot pain.

AS affects women during their peak reproductive years, but it does not appear to affect fertility.

Women with AS who are pregnant or trying to conceive should work with their doctors to find the right medications and to keep inflammation well managed.

Symptoms such as stiff spine and back pain can continue throughout pregnancy.

Nonsteroidal anti-inflammatory drugs (NSAIDs) such as ibuprofen (Advil) often help relieve pain from AS, but they can cause harm to your unborn child.

Other medications can pass through breast milk to your baby.

Women often have a higher disease burden because of a diagnosis delay. That means the disease may be more severe and arthritis more significant by the time women begin treatments.

One study found that that women are less responsive to TNF inhibitors (TNFi), a type of medication used to reduce inflammation in people with AS.

The same study also found, however, that women are significantly less likely to stick to their drug treatment regimen.

Otherwise, treatment for men and women is largely the same. The goal of treatment is to manage symptoms, as there is currently no cure, and to prevent damage.

Medications can be used to help reduce pain and inflammation. Physical therapy may help improve posture, flexibility, and strength.

In severe cases, surgery may be needed to repair or replace severely damaged joints.

AS was once thought to be more prevalent in men. Now, however, we know that may be due to underdiagnosis in women.

Also, women are more likely to have more advanced disease at the start of treatment due to delayed diagnosis.

Further research has determined that there’s little difference in symptoms of AS in men and women.

While men may have more foot pain and women may have more pain in their neck, knees, and hips, the primary symptom for both groups is back pain.

So then, if the symptoms are so similar, why does it take longer to diagnose women?

Part of the problem is that research has focused heavily on men, but that’s starting to change. Some recent studies have included more women, but there’s not enough data yet to reach firm conclusions about gender differences in AS.

AS is rare. Less than 1 percent of Americans have the chronic inflammatory disease. However, newer research suggests it may be underdiagnosed in general and specifically in women.

Having once thought to be a condition that primarily impacted men, we now know that more women are impacted than once known.

Because women tend to be diagnosed much later than men, the disease burden is greater. This means women may experience more symptoms and start treatment later. Those factors can cause significant issues in the future.

If you have symptoms of AS, such as persistent back or neck pain, see your primary care doctor as soon as possible. If it appears to be an inflammatory condition, you’ll likely be referred to a rheumatologist for evaluation.

After diagnosis, it’s important to see your rheumatologist at least once a year, even if your symptoms are currently mild.

There’s currently no cure for AS. But early detection and treatment can help alleviate pain and may prevent disease progression in both men and women.