Ankylosing spondylitis (AS) is a chronic inflammatory disease that primarily affects the spine, sacroiliac joint, and peripheral joints. In some cases, it can affect a person’s kidney health.

Researchers do not fully understand the effects that AS has on the kidneys, but they have some idea about the connection between AS and kidney involvement.

The following article discusses what the medical community knows about how AS can affect the kidneys.

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Research indicates that AS is associated with several potential kidney issues. However, experts generally consider kidney involvement a rare occurrence in a person living with AS.

According to a 2018 study, secondary renal amyloidosis is the most common type of kidney involvement in AS.

Secondary renal amyloidosis is a type of disease where the body deposits protein in the kidneys. The protein forms a fibrous deposit that builds up slowly over time. As the growth gets larger, the kidneys typically lose more of their ability to function.

Evidence also suggests that AS can lead to chronic kidney disease. In a 2019 study, researchers sought to understand the connection between chronic kidney disease and AS. They found that males experienced chronic kidney disease more frequently and severely than females.

They also noted that renal involvement in people living with AS is 8–22%.

Comorbidities, including hypertension, gender differences, other complications, and the use of nephrotoxic medications (medications that negatively impact the kidneys) all played a role in increasing a person’s risk factor for kidney disease and dysfunction.

Finally, AS has an association with Immunoglobulin A Nephropathy (IgAN). According to a 2020 study, IgAN is the most common cause of kidney lesions associated with AS.

Researchers still do not fully understand IgAN. What they do know is that it occurs when the immune system releases Immunoglobulin A (IgA) to fight infection. The protein then gets stuck in the kidney, causing inflammation and damage.

Over time, it can lead to a loss of function and kidney failure.

According to a 2019 study, AS is associated with the development of kidney disease. In this study, researchers noted that risk factors for kidney disease include:

  • being male
  • using medications that can damage the kidneys
  • the presence of other complications
  • other comorbidities such as high blood pressure

Though there are limited studies available, people living with AS have reported kidney stone formation.

One older study from 2012 confirmed the association between AS and kidney stone formation. However, the researchers noted that the association might be due to medications or other factors associated with AS instead of AS directly.

A 2016 study had similar findings. Researchers indicated that people living with AS have a higher likelihood of developing kidney stones than those not living with AS.

In rare cases, AS can cause neurological complications.

According to the Spondylitis Foundation of America, AS can cause cauda equine syndrome, where the nerves at the base of the spine are damaged.

If this occurs, a person may experience several symptoms, including possible urinary incontinence and retention.

Treatment varies based on what is causing the issues with the kidneys. If medication is a problem, a person’s doctor may recommend stopping and using a different treatment option. In those cases, the kidney issues may start to get better.

Controlling AS symptoms and inflammation may also help reduce the buildup of harmful proteins in the kidneys.

According to the National Institute of Diabetes and Digestive and Kidney Diseases, if IgAN is the cause of issues, treatment may consist of:

  • controlling the immune system response
  • reducing blood pressure
  • removing extra fluid from the blood
  • reducing cholesterol levels

People should talk with their doctor about specific treatment options for their kidneys if they develop problems associated with AS.

It may not be possible to prevent kidney issues from developing. A person should follow their treatment plan to help keep their AS under control, which may prevent complications such as kidney disease or injury.

People should also talk with their doctor about their medications and the risks associated with them. A doctor may prescribe a different set of medications that are less likely to damage the kidneys.

A person living with AS should maintain regular communication and checkups with their doctor to best monitor the condition.

They should talk with their doctor if they start to notice signs that their kidneys may not be functioning properly. General signs and symptoms of kidney problems can include:

  • blood in the urine
  • foamy urine (due to a large amount of protein in it)
  • pain or discomfort when urinating
  • development of other unusual symptoms

AS can cause issues with a person’s kidneys. Over time, excessive inflammation and buildup of proteins in the kidneys can cause damage that may lead to lesions, chronic kidney disease, loss of function, or, potentially, renal failure. A person should talk with their doctor about any unusual symptoms they experience and work with them on developing a treatment plan to address possible kidney issues.