Psoriatic arthritis (PsA) is an autoimmune disorder that causes joint inflammation and pain throughout the body. It most commonly affects the fingers, toes, knees, and ankles. PsA is one of several conditions that can cause sacroiliitis, which is inflammation of the sacroiliac joints. Sacroiliitis causes pain in the lower back, hips, buttocks, and legs. Here’s a look at how these two conditions are connected and how to manage the joint pain they cause.

What is PsA?

PsA is a chronic inflammatory condition where the immune system attacks and inflames the joints. It affects about 30 percent of people who have a diagnosis of psoriasis. Psoriasis is a skin condition characterized by scaly white and red patches on the skin. PsA most often affects joints like the fingers and toes. It can also cause inflammation in joints of the knees, ankles, back, and pelvis. Swelling and pain may affect only one joint or multiple joints. PsA symptoms may include:
  • pain, tenderness, stiffness, and swelling in the joints and in the tendons
  • reduced range of motion
  • fatigue
  • pitting and other changes to the nails
  • redness and pain in the eye
Without treatment, PsA can progress and cause permanent damage to the joints. Fortunately, many treatments can help slow the disease progression and minimize complications.

What is sacroiliitis?

Sacroiliitis is inflammation of one or both of the sacroiliac joints in the lower back. Two sacroiliac joints connect the bones at the top of your pelvis (the ilium) to the lower part of your spine (the sacrum). They support the weight of your upper body as you walk. The main symptom of sacroiliitis is pain in your lower back, buttocks, hips, or thighs. The pain may feel dull and achy or sharp and stabbing, and it can radiate down your legs. It typically hurts more when you sit or stand for a long period of time, climb stairs, or stand up from a chair. It can be challenging for doctors to diagnose sacroiliitis because so many other conditions also cause lower back pain. Having PsA is one clue that can point your doctor to a sacroiliitis diagnosis since the two conditions often exist together.

What’s the difference between PsA and sacroiliitis?

Sacroiliitis describes inflammation that affects specific joints in your lower back (the sacroiliac joints). Psoriasis is an inflammatory autoimmune disease that can cause inflammation in joints and ligaments throughout the body. It most often affects the hands and feet but can sometimes impact the pelvis and lower back. PsA is one of several conditions that causes sacroiliitis. Other inflammatory conditions that may result in sacroiliitis include:
  • ankylosing spondylitis (AS)
  • reactive spondyloarthropathy
  • juvenile idiopathic arthritis
  • osteoarthritis (OA)
Injury, pregnancy, and infection are also sometimes responsible for sacroiliitis.

How are PsA and sacroiliitis connected?

PsA can sometimes affect the sacroiliac joints and cause sacroiliitis. One small study found that nearly 38 percent of people with PsA had evidence of sacroiliitis on an MRI scan. Most didn’t have any sacroiliitis symptoms. Inflammation of the sacroiliac joint is sometimes one of the earliest signs of PsA. Treating this inflammation can prevent future pain in your lower back.


PsA treatment goals include reducing inflammation and pain and possibly preventing future joint damage. Some treatments address both PsA and sacroiliitis.

Over-the-counter treatments

Over-the-counter nonsteroidal anti-inflammatory drugs (NSAIDs) include ibuprofen (Advil, Motrin) and naproxen (Aleve). They treat mild joint inflammation and pain. Other NSAIDs can be prescribed by your physician.

Traditional disease-modifying antirheumatic drugs (DMARDs)

For sacroiliitis caused by PsA, you may need stronger disease-modifying antirheumatic drugs (DMARDs). These systemic medications address the root cause of PsA to slow the progression of PsA and help prevent joint damage. Traditional DMARDs suppress an overactive immune system to bring down inflammation throughout the body. Examples include:
  • cyclosporine (Neoral, Sandimmune)
  • methotrexate (Rheumatrex, Trexall)
  • sulfasalazine (Azulfidine)


Biologics are a newer type of DMARD that block specific proteins in the immune system linked to the inflammatory response in PsA. They’re given as an injection or infusion to help reduce inflammation and PsA symptoms. TNF inhibitors are a group of biologics that target the protein TNF-alpha. They include: Interleukin 17 (IL-17) inhibitors target the protein IL-17. Options include:
  • brodalumab (Siliq)
  • ixekizumab (Taltz)
  • secukinumab (Cosentyx)
Other biologics include interleukin 23 (IL-23) inhibitors, interleukin 12 and 23 (IL-12, IL-23) inhibitors, and T-cell inhibitors. Each of these drugs has specific functions and potential side effects. Talk to your doctor about which may be best for you.

Other treatments

Although DMARDs are often very effective at treating the root causes of PsA and sacroiliitis, they can take several months to work. Steroid injections are a faster treatment to reduce both PsA and sacroiliitis symptoms in the short-term. They can help bring down swelling in your joints until DMARDs or biologics take full effect. Physical therapy can also address both PsA and sacroiliitis symptoms. A physical therapist can teach you exercises designed to improve the flexibility, strength, and range of motion in your joints. Rarely, you might need surgery to fuse the bones in a painful joint together. Connecting the bones helps to stabilize the joint and reduce pain.

The takeaway

PsA is an autoimmune disease that can cause inflammation in joints throughout the body. It can sometimes cause sacroiliitis, an inflammation in the joints of the lower back. If you have PsA, there’s a chance you could also have sacroiliitis. Let your doctor know if you have pain in your lower back, legs, or hips. An MRI can help your doctor to make a diagnosis. If you have PsA or sacroiliitis, it’s important to begin treatment to reduce inflammation in your joints. Early treatment can prevent long-term complications and permanent joint damage.