Early stages of ankylosing spondylitis may involve unexplained lower back pain and stiffness that come and go. Fatigue and pain in your heels, chest, and some joints are also possible symptoms.

Back pain is a top medical complaint. It’s also a leading cause of missed work.

Possible causes of low back pain may vary and include trauma from a sudden strain on the spine. Unexplained back pain may sometimes signal a condition called ankylosing spondylitis (AS).

AS is a chronic autoimmune condition resulting from inflammation in the vertebrae of the spine. It’s a form of spinal arthritis.

Not everyone with AS experiences early symptoms. When they do, symptoms may appear at any age between 20 and 40 years old. Children may also develop juvenile ankylosing spondylitis (JAS).

Early signs and symptoms of AS and JAS may include:

Unexplained pain in the lower back

Pain related to AS is often located in the sacroiliac joints. This is where your sacrum, the triangular bone at the bottom of your spine, and ilium, the upper hip bone, meet in the lower back.

Typical back pain often feels better after rest. AS may be the opposite. You may experience pain and stiffness upon waking or after resting.

In the same way, while exercise may make other types of back pain worse, AS symptoms may actually decrease after physical activity.

Lower back pain for no apparent reason isn’t typical in younger people. Teens and young adults who complain of stiffness or pain in the lower back or hips may benefit from a medical consultation.

Unexplained stiffness and pain in other body parts

Pain in different areas of the body is also a common early symptom of AS and may include:

  • pain in the heels or arch of your feet
  • pain and stiffness in the joints of the wrists, ankles, or knees
  • pain in the rib bones or breastbone

Tightness in the chest with difficulty breathing and stiffness after resting are also possible symptoms of AS.

Some people may experience pain in the hips and knees first, followed by lower back pain.

Pain that comes and goes but eventually worsens

AS is a progressive disease. Although physical activity or pain medications may help temporarily, the condition gradually worsens.

At first, you may notice your symptoms come and go, but they won’t stop completely. Stiffness and pain may be worse some days and then decrease in intensity.

As time passes, the pain may spread from the lower back to the rest of the spine.

If left untreated, AS may lead vertebrae to fuse, or grow together, causing a forward curvature of the upper spine called kyphosis.

Getting an early diagnosis and treatment may slow the intensity of the pain and kyphosis.

Pain that improves with movement

Experiencing pain at night and feeling better once you get up is a common early symptom of AS.

At first, people with AS get symptomatic relief from taking common over-the-counter nonsteroidal anti-inflammatory drugs (NSAIDs), such as ibuprofen or naproxen. However, these medications won’t alter the course of the disease.

Changes in your bones

Slight damage to the tissues surrounding your cartilage and spine bones is an early sign of AS that may become obvious in X-rays.

Fusion of the bones between your hips and pelvis may start to happen. Inflammation may also lead to a “squaring” of your vertebrae, which could be seen in lateral X-rays of your spine.

It’s also possible a radiologist notices deterioration of the corners of these bones.

AS is not the only condition that may lead to pain and stiffness that worsens with rest. These and other symptoms may have other causes, including:

  • fibromyalgia
  • herniated disks
  • rheumatoid arthritis
  • degenerative disk disease
  • scoliosis
  • osteoporosis
  • infections
  • tumors
  • injuries

Only a healthcare professional can provide an accurate diagnosis. If you have unexplained pain and stiffness that does not improve over time, consider consulting a healthcare professional for an assessment.

Typically, AS pain is dull and ongoing. Generally, you may feel some of the following:

  • stiffness and increased pain in the morning after waking up lessen throughout the day as you move around
  • pain worsens during sleep, which can wake you up
  • light physical activity, stretching, or a hot bath or shower offer pain relief
  • pain moves from side to side, especially at first
  • symptoms ease temporarily and then return later
  • pain and inflammation develop in other parts of the body, such as the ribs, shoulders, knees, ankles, feet, heels, and Achilles tendon

In addition to pain, other AS symptoms may include:

  • fatigue and low energy
  • restricted movement in the chest, which makes it hard to breathe
  • painful and red eyes
  • neurological symptoms, such as referred pain or muscle weakness
  • cardiovascular problems, such as inflammation of the aorta, aortic valve disease, and ischemic heart disease

Intermittent flare-ups of pain and stiffness in your spine are common in AS.

In the past, experts thought AS may be more common among young males, but new evidence indicates the condition is as common in males as in females.

Initial symptoms usually appear in the late teen to early adult years. AS can develop at any age, however.

The tendency to develop the disease is inherited. A genetic marker called HLA-B27 can indicate an increased chance of AS.

However, not everyone who develops AS has this gene. And when the gene is present, it doesn’t mean you’ll definitely develop AS.

It’s unclear why some people get AS and others don’t.

You may be more likely to develop AS if you have a close relative who lives with:

  • AS
  • psoriatic arthritis
  • arthritis related to inflammatory bowel disease

A history of genitourinary infections may also increase the risk of developing AS, according to the National Institute for Health and Care Excellence (NICE).

No single test exists for AS. Diagnosis may involve:

  • physical exam and questions about pain location, frequency, and intensity
  • mobility testing to determine flexibility and ease of movement
  • blood tests for inflammation, such as sedimentation rate and C-reactive protein
  • blood tests for genetic markers, such as HLA-B27
  • imaging tests, such as a CT scan, MRI scan, or X-rays, to determine bone health

Some experts believe an MRI may be able to diagnose AS earlier than an X-ray because it can detect premature inflammatory changes in the affected joints.

However, this may not always be the case. It depends on your health needs, other test results, and proposed treatment decisions you and your healthcare team agree on.

If you find that your lower back pain (or pain in other joints) is lasting longer than you expected or you find that symptoms worsen with rest, you may want to contact a healthcare professional for testing.

AS has no known cure yet, but you can reduce your symptoms and slow the progression of the disease by:

  • getting a diagnosis as early as possible
  • starting medical treatment as soon as possible after that
  • practicing specific physical therapy and postural training exercises

What causes low back pain?

Low back pain can have many causes. If it’s a temporary symptom, low back pain could result from muscular tension, uncomfortable posture, lack of regular physical activity, a sprain, or a strain.

If your low back pain is persistent or comes and goes, causes may include ankylosing spondylitis, fibromyalgia, rheumatoid arthritis, other types of arthritis, herniated disks, tumors, or osteoporosis. Only a healthcare professional can provide an accurate diagnosis.

Where does ankylosing spondylitis pain start?

It depends. Ankylosing spondylitis may begin as stiffness and pain in your lower back that comes and goes and may worsen after rest. Some people may also experience knee, ankle, and heel pain during the early stages of ankylosing spondylitis.

As the condition progresses, the pain may become more persistent and extend to the mid and upper back. You may also experience fatigue, eye irritation, and stiffness.

What is the average age of ankylosing spondylitis?

The onset of ankylosing spondylitis is typically between 20 and 40 years, although you may develop the condition at any age.

What are the three most common symptoms of ankylosing spondylitis?

Every body is different, but common early symptoms of ankylosing spondylitis include fatigue, low back pain, and stiffness.

As the condition progresses, you may also experience joint pain in other areas of the body, eye irritation, chest pain, gastrointestinal challenges, difficulty breathing, curving of the spine (kyphosis), and general back pain.

Ankylosing spondylitis (AS) is a progressive inflammatory condition that affects your spine and other body parts. Some people experience no early symptoms, while others may have lower back pain and stiffness that comes and goes.

AS pain usually decreases with physical activity and worsens at rest. Fatigue, gastrointestinal upset, and eye irritation may be early symptoms of AS.

Some symptoms common to AS may result from other conditions. Only a healthcare professional can offer you a comprehensive assessment and accurate diagnosis.