Ankylosing spondylitis typically causes pain in the lower back, but it may also affect the legs. Some may confuse the pain with sciatica or other forms of arthritis. A doctor can provide a diagnosis and suitable pain relief.

Ankylosing spondylitis (AS) is a type of arthritis that causes inflammation in the spine. Over time, the ligaments and joints of the spine become stiff, and in severe cases, the bones fuse together. This can lead to ongoing pain and a loss of flexibility in the back.

Some people with AS have mild episodes of back pain and stiffness that may come and go. Other individuals may develop symptoms in areas such as the hips, knees, and ankles. As such, in some cases, AS may result in leg pain.

Read on to learn more about how AS may affect the legs and how it differs from sciatica.

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The Spondylitis Association of America (SAA) states that the hallmark feature of AS is the involvement of the sacroiliac (SI) joints during the progression of the disease. The SI joints are at the base of the spine, where the spine joins the pelvis.

According to the SAA, it is important to note that the course of AS varies significantly from person to person. In a minority of individuals, pain does not start in the lower back or neck but in a peripheral joint such as the hip, ankle, elbow, knee, heel, or shoulder.

The SAA explains that inflammation commonly happens when a tendon or ligament attaches to a bone, so it can affect joints in the leg.

Individuals may experience different symptoms, and the course of AS varies from person to person. The SAA explains that the most common symptoms of AS are frequent pain and stiffness in the lower back and buttocks, which comes on gradually over the course of a few weeks or months.

Symptoms of AS that may affect the legs include:

  • inflammation of the joints, causing pain and stiffness in the knees or hips
  • enthesitis, which is painful inflammation of the connective tissue between a tendon or ligament and bone, such as the top of the shin bone or the heel
  • fatigue or tiredness in the legs

Learn how to recognize AS symptoms.

Since some people experience AS that starts in the legs rather than the back, it may be difficult to distinguish AS from some other forms of arthritis. Additionally, due to symptoms presenting as pain in the lower back and legs, some individuals may confuse these symptoms with sciatica.

Sciatica is a condition that causes pain in the legs and lower back due to compression of the sciatic nerve. People may also experience a burning sensation deep in the buttocks and a feeling that their legs are weak and heavy.

Doctors may initially test for sciatica by asking someone to perform a straight leg raise to find out whether this causes pain. However, this test is not conclusive, and doctors will typically require additional information to make a diagnosis.

Additionally, sciatica can be a symptom of cauda equina syndrome, which is a very rare complication of AS that happens when the nerves at the bottom of the spine become compressed. Other symptoms of cauda equina syndrome include weakness or numbness in both legs and difficulty managing urination and bowel movements.

People experiencing leg pain or other symptoms should talk with a doctor for a diagnosis.

Learn about potential complications of AS.

Health experts advise that treatment should focus on relieving pain and stiffness, maintaining functional ability, and helping to prevent complications. A doctor may recommend the following treatment options:

Learn more about AS treatment options.

Individuals experiencing pain or other symptoms affecting the legs or back should contact a doctor for a diagnosis.

AS may feel similar to some other forms of arthritis or other conditions that cause symptoms in the legs. These may include:

If a person with diagnosed AS starts to experience new symptoms, they should discuss management of these symptoms with a healthcare professional. They may need medication adjustments or further treatment recommendations.

Although lower back pain is the hallmark feature of AS, some individuals may have leg pain in addition to or instead of back pain. This may mark the onset of symptoms and may progress to back pain in time.

Leg pain can be a symptom of sciatica, which can relate to AS. Additionally, other forms of arthritis may present similarly to AS. Because of this, it is essential that a person with symptoms of AS contacts a doctor for a diagnosis.