Psoriatic Arthritis vs. Sacroiliitis: What Are the Differences?

Psoriatic arthritis (PsA) is a type of inflammatory arthritis that causes joint inflammation and pain throughout the body. It most commonly affects the fingers, toes, knees, ankles, and the entheses, the areas where tendons and ligaments meet bone.

PsA often causes a condition called sacroiliitis, which is inflammation of the sacroiliac (SI) joints. Sacroiliitis commonly causes pain in the hips, low back, buttocks, and legs. This article will discuss how these two conditions relate, including symptoms, causes, and treatment.

Symptoms

Sacroiliitis is seen in 34%–78% of people who have psoriatic arthritis. It also affects up to 23% of people with psoriasis who do not have peripheral joint involvement. Psoriasis is an inflammatory skin condition that causes skin cell growth to speed up and build up as scales on the skin.

Psoriatic Arthritis

PsA affects around 0.06%–0.25% of the American population. The prevalence of PsA is low in the general population, but it is very common in people who have psoriasis. According to the National Psoriasis Foundation, it affects about 30% of people with psoriasis.

The main symptom of PsA is pain, swelling, and stiffness in and around the joints. This is because it is an autoimmune disease in which the immune system malfunctions and attacks healthy parts of the body. PsA is also a type of spondyloarthritis, a group of inflammatory conditions that affect the back, pelvis, neck, and some larger joints.

Additional symptoms of PsA include:

• Joint stiffness: Joint stiffness lasts more than 30 minutes in the morning and after being inactive for long periods.
• Enthesitis: This is inflammation that causes tenderness where connective tissue attaches to bone. Pain is felt when pressure is applied to these areas. The knees, hips, elbows, and chest also might be affected. It can also cause pain in the heel or the bottom of the feet closest to the heel, including pain with standing and walking.
• Dactylitis: Sometimes called sausage digits, dactylitis causes the fingers and toes to become so swollen they resemble small sausages. It usually affects one or two digits at a time.
• Fatigue: Feelings of being overtired can be severe and persistent and doesn’t resolve with rest.
• Nail symptoms: These include pitting (tiny dents), ridges, nail discoloration, and nail bed separation.
• Skin symptoms: These include a rash that presents as thick, red patches of skin covered by silvery scales. Skin patches can be itchy and sore. They can appear anywhere on the body but are frequently seen on the elbows, knees, lower back, scalp, face, hands, and soles of the feet.
• Chest and rib pain: While rare, chest and rib pain can lead to shortness of breath. This is often the result of chest wall and rib cartilage inflammation. PsA can also cause lung or aorta (the large blood vessel that leaves the heart) inflammation.
• Eye inflammation: Eye dryness, eye pain, and conjunctivitis (pink eye) are common in people with PsA. PsA also causes uveitis, inflammation of the middle layer of the eye. While uveitis is a less common symptom of PsA, it can lead to permanent eye damage and vision loss if left untreated.

Inflammation of the SI joints is one of the earliest signs of PsA. According to a small study reported in 2020, nearly 38% of participants with PsA showed evidence of sacroiliitis on imaging tests, and most were not reporting symptoms of the condition. Treating inflammation can prevent future back and spine problems in people with PsA.

Sacroiliitis

People with sacroiliitis have inflammation in one or both SI joints. The condition is either asymmetric (affecting one side) or symmetric (affecting both sides).

The SI joints sit between your sacrum and iliac bones in the lower back, at the area where the spine and pelvis meet. Their job is to carry the weight of the upper body when you are standing or walking.

Doctors are unsure how many people are living with sacroiliitis. According to Cleveland Clinic, it may affect 10%–15% of people who report back pain.

Common symptoms of sacroiliitis are:

• Painful and inflamed SI joints that cause pain in the lower back, buttocks, hips, thighs, and groin
• Pain that extends into one or both legs, or even into the feet
• Pain that feels dull, achy, sharp, or stabbing
• Pain that feels worse after sitting or standing for long periods or when getting up from a sitting position
• Pain that worsens when the hips are rotated
• Stiffness of the hips and low back, especially after getting out of bed in the morning or after sitting for a long time
• Low-grade fever that accompanies pain and stiffness

Left untreated, sacroiliitis can affect your mobility. Untreated pain can make it harder for you to perform daily tasks, can disrupt your sleep, and can affect your mental health.

Sacroiliitis linked to conditions like PsA and ankylosing spondylitis (another type of spondyloarthritis) can worsen with time and potentially affect the bones of your spine (the vertebrae), causing them to stiffen and fuse. 

Fusing means the vertebrae grow together due to the calcification of the ligaments and discs between the vertebrae. When this occurs, the spine becomes immobile, brittle, and vulnerable to fractures.

Causes

PsA is an autoimmune disease that occurs when the body’s immune system malfunctions and attacks healthy cells. The overactive response causes inflammation of the joints and other body areas and the overproduction of skin cells.

Researchers don’t know why the immune system malfunctions and causes PsA. But they theorize that PsA is triggered by a mix of genetic and environmental factors.

The most well-known genes linked to PsA are those of the human leukocyte antigen (HLA) complex. These antigens help the immune system recognize the difference between the body’s normal proteins and foreign invaders, like bacteria and viruses.

Some variations of HLA genes are linked to the different types of PsA and PsA disease severity and progression. There are also non-HLA genes linked to PsA that affect the signaling of the immune system.

PsA can run in families. It is estimated that 40% of people with the condition have at least one family member with PsA or psoriasis. This means that if you have a close family member with PsA (a parent or sibling), you might be at an increased risk for PsA and/or psoriasis.

Some people with psoriasis are also at an increased risk for PsA. These might include people who have severe psoriasis, those who experience nail symptoms, and those with inflammatory eye disease.

Environmental factors might play a role too. Injuries, infections, chronic stress, cigarette smoking, alcohol consumption, and exposure to certain medicines can trigger disease development, especially in people with a family history of PsA.

Sacroiliitis

Inflammation of the SI joints is what causes sacroiliitis. It is often linked to different types of inflammatory conditions. Many types of arthritis can lead to inflammation of the SI joints, including:

• Osteoarthritis: A type of wear-and-tear arthritis that can affect the spine and the SI joints, leading to degeneration of the SI joints and SI joint pain
• Any spondyloarthritis, including ankylosing spondylitis (inflammatory arthritis of the spine), and PsA
• Other types of rheumatological disease like rheumatoid arthritis (RA) or lupus

Other causes of sacroiliitis include:

• Trauma: A fall, motor vehicle accident, or another injury that affects the lower back, hips, or buttocks could lead to symptoms of sacroiliitis.
• Pregnancy and childbirth: Pregnancy hormones can relax muscles and joints in the pelvis, and the pelvis stretching and widening from childbirth can stress the SI joints.
• Pyogenic sacroiliitis: An infection of one or both of the SI joints can lead to sacroiliitis.

Diagnosis

There is no specific test to diagnose PsA. Diagnosis is based on symptom history and a physical examination. You should let your doctor know about any family history of PsA or psoriasis.

Sacroiliitis can sometimes be harder to diagnose because low back pain has many causes. But much like PsA, diagnosis starts with a medical history and a physical exam.

Psoriatic Arthritis

A physical exam of PsA includes a checkup of joints, entheses, skin, and nails. Your healthcare provider will examine joints by touch to determine the amount of swelling and tenderness of each joint. Joints assessed will include the fingers, toes, hands, wrists, elbows, shoulders, hips, knees, ankles, feet, sternum (breastbone), and jaws.

Your healthcare provider will also examine the entheses to determine if there are sore and tender areas. Enthesitis classically affects the heel and the bottom of the foot, including areas around the knees, pelvis, spine, rib cage, shoulders, and elbows.

Skin examination for PsA looks for signs of psoriasis, including scaly red papules and plaques on the skin. Nail involvement in PsA might show nails that have ridges and nail bed separation.

Additional testing for PsA includes:

• Imaging studies­—X-rays, magnetic resonance imaging (MRI), and ultrasound scans—to check for evidence of joint or bone damage
• Rheumatoid factor and anti-cyclic citrullinated peptide (anti-CCP) testing to rule out rheumatoid arthritis
• Joint fluid testing to look for the presence of uric acid crystals to rule out gout, a common form of arthritis causing sudden joint pain

Sacroiliitis

Physical examination of sacroiliitis starts by checking the spine for proper alignment and movement. You will be asked to move in specific directions to see what movements cause pain or where stiffness exists.

In addition, your healthcare provider might apply pressure to the SI joints, spine, hips, or legs. The more pain the applied pressure brings, the more likely a sacroiliitis diagnosis will be made.

Additional testing includes:

• Bloodwork: These tests look for inflammatory blood markers.
• Imaging studies: X-rays, computed tomography scans, and/or MRIs will check for injuries or changes in the SI joints.
• Steroid injection: If the injection relieves pain, then a diagnosis of sacroiliitis can be made. This injection is done using an X-ray to guide the spinal needle to the correct location for the injection.

Treatment

The main goal of treating PsA is to control the inflammation that affects the joints and skin. That will ease pain, improve symptoms, and prevent further damage. There are plenty of treatment options to help ease symptoms and protect your joints.

Treatment for sacroiliitis depends on the signs and symptoms experienced as well as the cause of those symptoms.

Psoriatic Arthritis

Medications are often helpful for managing PsA, and surgery might be an option if joint damage occurs. Your treatment options will depend on how severe your symptoms are. You may need to try more than one medication before finding one that works best to manage symptoms.

You can also add lifestyle changes and complementary and alternative medicine (CAM) therapies to your treatment plan.

Medicines used to treat PsA include:

• Nonsteroidal anti-inflammatory drugs (NSAIDs): If your PsA is mild, your doctor may recommend an NSAID, such as Aleve (naproxen) or Advil or Motrin (ibuprofen). These medicines can stop the body from causing inflammation. NSAIDs also treat pain.
• Disease-modifying antirheumatic drugs (DMARDs): For severe PsA, these drugs can slow or stop pain, swelling, and joint and tissue damage. They are stronger than NSAIDs, and they usually take longer to work. The most prescribed DMARDs are Trexall (methotrexate), Arava (leflunomide), and Azulfidine (sulfasalazine).
• Immunosuppressants: If you can’t take DMARDs, your doctor might suggest an immunosuppressant drug to manage the effects of your overactive immune system. Examples of immunosuppressants prescribed for PsA are Azasan (azathioprine) and Gengraf (cyclosporine).
• Biologics: These drugs block proteins responsible for inflammation. Examples used to treat PsA are Orencia (abatacept), Humira (adalimumab), Remicade (infliximab), Taltz (ixekizumab), and Cosentyx (secukinumab). Biologics are given as a shot under the skin or by intravenous (IV) infusion.
• Enzyme inhibitors: An enzyme inhibitor drug called Otzela (apremilast) can manage conditions like PsA by reducing long-term inflammation. It is a pill that works by blocking a specific enzyme called PDE-4.
• Corticosteroids: These are powerful anti-inflammatory drugs that help to relieve pain and swelling. They are given either in pill form or injected directly into a joint or muscle. These drugs are only given for short periods because they can make skin symptoms worse.

Additional treatments for PsA are surgery, light therapy, lifestyle changes, and CAM therapies.

• Surgery: Most people with PsA will never need surgery. But when joint deformity has occurred, a person might experience severe pain and mobility problems. Surgery can help to relieve pain, restore joint function, and help you to move again.
• Light therapy: Exposing psoriasis-affected skin to ultraviolet (UV) light can help to get rid of psoriasis skin plaques.
• Lifestyle: It is important to stay active to keep joints and muscles loose, lessen the workload of joints, and keep inflammation in check. Walking, swimming, and biking are all good exercises to keep joints moving. Additional lifestyle measures that might help are eating a healthy diet, managing stress, getting plenty of rest, and not mixing PsA medications with alcohol.
• CAM: Examples of CAM therapies that might help you manage PsA symptoms include acupressure and acupuncture, massage, tai chi, and yoga.

Sacroiliitis

Sacroiliitis is managed with medications, physical therapy, lifestyle therapies, and different types of medical procedures.

Depending on the cause of symptoms, medicines used to treat sacroiliitis might include:

• Pain relievers: Your healthcare provider will initially recommend over-the-counter pain relievers, but if those don’t help, they can prescribe stronger versions of these medicines.
• Muscle relaxers: Muscle-relaxing medicines can help to reduce muscle spasms caused by sacroiliitis.
• Tumor necrosis factor (TNF) inhibitors: TNF inhibitors are a type of biologic drug therapies—such as Humira and Remicade—and can help relieve sacroiliitis related to spondyloarthritis conditions like PsA and ankylosing spondylitis.

A physical therapist can help you learn stretches and range of motion exercises to manage joint flexibility and stabilize muscles and joints.

Lifestyle and home remedies for managing sacroiliitis include modifying or avoiding activities that worsen pain to reduce inflammation in the SI joints. Proper posture also helps to improve symptoms. Alternate between ice and heat to help relieve SI pain.

Additional therapies for sacroiliitis include injectable corticosteroids, radiofrequency denervation to damage nerve tissue causing SI pain, and electrical stimulation to reduce pain. Joint fusion
surgery involves fusing affected bones to help relieve sacroiliitis symptoms.

Prevention  

PsA and sacroiliitis are not preventable conditions. Even though researchers know what some people have a higher risk for PsA (those with psoriasis or a family history of psoriatic disease), there is no treatment or tool to prevent a person from getting PsA.

Because sacroiliitis is generally caused by conditions that are not always preventable, it is not easy to avoid the condition. However, it might be possible to prevent or reduce symptoms of the condition by avoiding activities that cause pain and stiffness. 

Summary

Psoriatic arthritis is a type of inflammatory arthritis that causes joint pain and inflammation throughout the body. It might also cause a skin rash and other symptoms like eye inflammation. Psoriatic arthritis is one of several conditions that lead to sacroiliitis, or inflammation of the sacroiliac joints. Sacroiliitis causes pain and stiffness in the low back, hips, buttocks, and legs.

A Word From Verywell

People with PsA are at a higher risk for sacroiliitis. If you have PsA and start to experience pain in your lower back, hips, and buttocks, reach out to your doctor. An MRI can help your doctor see inflammation occurring in the SI joints and make a diagnosis.

If you are diagnosed with sacroiliitis, it is important to keep PsA inflammation under control and properly manage symptoms that affect your SI joints. Early and aggressive treatment can prevent complications and permanent joint damage.