Psoriatic arthritis (PsA) is a chronic inflammatory joint disease that affects some people with psoriasis. PsA can affect multiple body tissues, including the joints, skin, and nails. Doctors use various tests and specific criteria to diagnose it.
In PsA, an overactive immune system mistakenly attacks healthy body tissues, resulting in pain and inflammation. It is unclear why some people with psoriasis develop PsA while others do not.
This article describes PsA, including the different types. We also provide information on diagnosing and treating PsA and offer advice on when to consult a doctor. Finally, we cover the outlook for people living with PsA and compare the differences between PsA and rheumatoid arthritis.
PsA is a form of chronic inflammatory arthritis that affects around 15% of people with the skin condition psoriasis. Medical experts do not yet understand why some people with psoriasis go on to develop PsA while others do not.
PsA can cause pain and inflammation in multiple body tissues, including:
- the joints, such as:
- large, weight-bearing joints
- smaller joints in the fingers and toes
- joints of the spine and pelvis
- gastrointestinal tract
Psoriasis and PsA are autoimmune conditions in which the immune system mistakenly attacks healthy body cells and tissues. Experts do not fully understand what causes these conditions. However, around 40% of people with PsA have a family member with psoriasis or PsA, suggesting a genetic link.
There is no definitive test for PsA.
To diagnose the condition, a doctor will:
- take a detailed medical history
- perform a physical exam
- order imaging tests, which can detect inflammation in the joints
If preliminary investigations suggest that a person may have PsA, the doctor may make a referral to a rheumatologist. This is a doctor who specializes in disorders of the musculoskeletal system.
- blood tests to assess the following:
- erythrocyte sedimentation rate (ESR) and C-reactive protein (CRP) levels, which measure inflammation in the body
- rheumatoid factor (RF) and anti-cyclic citrullinated peptide (CCP) antibodies, which may warrant a diagnosis of RA rather than PsA
- antinuclear antibodies (ANAs), which can help exclude diseases like lupus
- levels of the different types of blood cells within a person’s blood
- kidney function, liver function, and electrolyte levels
- MRI scans, X-rays, and ultrasound scans to detect any inflammation and wear in the joints
There are five main types of PsA. These types differ according to the area of the body the condition affects, as well as the number of joints involved.
The five types of PsA are:
- Asymmetrical oligoarticular (AO) arthritis: This type affects fewer than five joints. Medical professionals refer to it as “asymmetrical,” as symptoms appear on only one side of the body. Around 35% of people with PsA have AO arthritis.
- Symmetrical polyarthritis (SP): This type affects five or more joints. Medical professionals refer to it as “symmetrical,” as symptoms appear on both sides of the body. The symptoms can occasionally resemble those of RA. Around 50% of people with PsA have SP, making this the most common type.
- Distal arthritis: This type affects the small joints at the ends of the fingers and toes. It may cause changes to the nails, such as spotting, pitting, and separation of the nail from the nail bed. Most cases of DA occur alongside another type of PsA, with only around 20% of people experiencing DA alone.
- Arthritis mutilans (AM): This is the most severe and destructive type of PsA, and it primarily affects the joints of the fingers, hands, wrists, and feet. This type may shorten and fuse joints, leading to joint deformity, stiffness, and immobility. Less than 5% of people with PsA have the AM type.
- Spondyloarthritis: This type affects the joints of the lower back and the pelvis. The main symptoms are back pain and morning stiffness.
Diagnosis of PsA can follow the CASPAR criteria, which stands for classification for psoriatic arthritis.
The criteria state that to receive a diagnosis of PsA, a person must first have received a diagnosis of inflammatory articular disease. Such diseases typically cause symptoms such as joint pain, swelling, and stiffness.
For a diagnosis of PsA using the CASPAR criteria, a person must also score at least three points from the options listed below:
- current active psoriasis: 2 points
- personal history of psoriasis, unless current psoriasis is present: 1 point
- family history of psoriasis, unless current psoriasis is present or there is a personal history of psoriasis: 1 point
- current or previous dactylitis, swelling of the fingers or toes: 1 point
- X-ray evidence of a new bone growth near a joint: 1 point
- rheumatoid factor (RF) negativity: 1 point
- nail issues, such as nail pitting and separation of the nail from the nail bed: 1 point
A person should consult a doctor if they have a personal or family history of psoriasis and begin to experience symptoms of PsA, such as persistent joint pain, swelling, or stiffness. A doctor will run tests to determine whether the person has PsA.
A person should also talk with a doctor if they have already received a diagnosis of PsA and experiencing a particularly severe or persistent flare of the condition. Symptoms may include:
- general tiredness or fatigue
- joint pain with swelling and stiffness, particularly in the mornings
- reduced range of joint movement
- tenderness, pain, and swelling over tendons
- swollen fingers and toes
- eye pain and redness
There are many treatment options for PsA. These treatments aim to:
- reduce symptoms
- slow the progression of the disease
- allow the joints to function as well as possible
- improve the person’s quality of life
- prevent or minimize complications
In 2018, the American College of Rheumatology (ACR) and the National Psoriasis Foundation (NPF) provided an evidence-based guideline for the treatment of PsA. Below are some of the treatments featured in these guidelines.
Nonmedical treatment options that may help to alleviate the symptoms of PsA include:
- physical therapy
- occupational therapy
- massage therapy
- quitting smoking
- losing excess weight
- performing regular exercise
The 2018 guidelines also list a range of medical treatments that may help alleviate the symptoms of PsA or help slow the progression of the disease. Examples are as follows.
Nonsteroidal anti-inflammatory drugs (NSAIDs)
NSAIDs block the production of prostaglandins that signal the body’s immune system to trigger an inflammatory response.
Glucocorticoids are steroid hormones that can help suppress the immune system and reduce inflammation and associated tissue damage.
According to the Psoriasis and Psoriatic Arthritis Alliance (PAPAA), a person may take low dose steroid tablets to help alleviate PsA pain and stiffness. Doctors may also prescribe a temporary high dose to help a person recover from a PsA flare.
In some cases, a person may receive an injection of steroids into the affected joints to reduce localized pain and inflammation.
Disease-modifying antirheumatic drugs (DMARDs)
DMARDs are medications that slow the biological processes responsible for causing chronic inflammation. In this way, DMARDs help slow the progression of PsA.
Psoriatic arthritis is a chronic condition that can worsen over time. Without treatment, severe cases may result in permanent joint damage and deformity. Such cases may require surgical treatment.
However, diagnosing and treating PsA in its earlier stages can help slow the progression of the disease and reduce the risk of permanent joint damage.
PsA and RA are both inflammatory forms of arthritis that occur due to the immune system attacking healthy body cells and tissues.
The key difference between the two conditions is that PsA involves the skin as well as the joints. Other differences include:
- Disease symmetry: RA affects joints on both sides of the body, whereas PsA may affect joints on one side of the body.
- Joints affected: RA typically affects the middle joints of the fingers and toes, while PsA typically affects the joints closest to the fingernails and toenails.
- Diagnostic markers: Blood tests for RA will usually reveal a positive RF or CCP antibody, whereas blood tests for PsA will typically reveal a negative RF and CCP. Doctors may use such tests to help differentiate between the two diagnoses.
PsA is a chronic inflammatory skin condition associated with the skin disease psoriasis. Both conditions occur due to the immune system mistakenly attacking healthy body cells and tissues.
A person should consult a doctor if they experience symptoms of PsA, especially if they have an existing diagnosis of psoriasis. Symptoms include joint pain, swelling, stiffness, and general fatigue.
Early diagnosis and treatment of PsA can improve the outcome for people living with the disease. The diagnostic procedure for PsA typically involves a combination of imaging tests and blood tests. Treatment options are varied and include NSAIDs, glucocorticoids, and DMARDs.