Psoriatic arthritis

Definitions & Key takeaways

Psoriatic arthritis is a type of inflammatory arthritis that will develop in some people with the chronic skin condition psoriasis. Psoriatic arthritis typically affects the joints of the fingers and toes, as well as the spine, hips, and knees, causing joint pain, swelling, and stiffness. Treatment includes NSAIDs, sulfasalazine, and methotrexate.

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Introduction0:00–0:38

In psoriatic arthritis, arthritis means joint inflammation, and psoriatic refers to psoriasis, which is an autoimmune disease characterized by red scaly patches in the skin.
So psoriatic arthritis is a type of joint inflammation that happens in individuals with psoriasis. Psoriatic arthritis is also one disease in a group of diseases called seronegative spondyloarthropathies.
Spondyloarthropathies are autoimmune diseases that affect the joints, and they’re seronegative, meaning that there aren’t any specific autoantibodies linked to them.

Physiology0:38–1:28

Normally, immune cells are ready to spot and destroy anything foreign that could cause the body harm. To help with this, most cells express the gene HLA-B27, which encodes a protein that forms a major histocompatibility complex, or MHC, class I molecule that sits on the surface of the cell membrane.
This MHC class I molecule acts like a serving platter, presenting molecules from within the cell for the immune system to sample.
A CD8+ T-cell, also called a cytotoxic T-cell, uses its T-cell receptor to bind to the antigen presented by the MHC class I molecule.
Normally, the antigen that’s presented is from the cell, and the immune system recognizes it as a harmless self-antigen, which leads to no response.

Causes1:28–2:00

Now, many individuals with psoriatic arthritis have a specific version of the gene HLA-B27, which somehow leads to an autoimmune process.
In these individuals, the immune system attacks self-antigens specifically ones in the joints. Exactly what causes this is unclear, but it's clear that the gene is not enough to trigger psoriatic arthritis.
Often, an environmental trigger like physical trauma or an infection seems to play a role as well. Ultimately, once the self-antigens are seen as foreign, T cells release cytokines which increases inflammation, and stimulates other immune cells to release Tumor Necrosis Factor or TNF, IL-12, and IL-23.

Pathology2:00–2:41

This triggers keratinocytes and fibroblasts to proliferate and leads to formation of a psoriatic plaque. In some individuals with psoriasis, T cells also go to the joints and trigger activation of osteoblasts and osteoclasts, leading to joint erosion and ossification, which can ultimately cause deformities.
Psoriatic arthritis is chronic and progressive, which means that it typically worsens over time. The symptoms of psoriatic arthritis include pain, swelling, and stiffness in the affected joints.

Symptoms2:41–4:24

And since psoriatic arthritis is inflammatory, these joints are generally red and warm to the touch. Now, different joints can be affected, and there are five different types of psoriatic arthritis.
In order from most to least common, they are oligoarticular, polyarticular or rheumatoid pattern, spondyloarthritis, distal interphalangeal predominant, and arthritis mutilans.
The oligoarticular type is typically very mild; often asymmetric in terms of joint involvement, and usually involves fewer than 5 joints.
The polyarticular type is also called rheumatoid pattern because it resembles rheumatoid arthritis. It is usually symmetric and affects five or more joints, including the joints of the hands, wrists, feet, and ankles.
The spondyloarthritic type is asymmetric and typically involves the spine and sacroiliac joint. It causes fusion of the vertebral bodies, and that leads to stiffness of the neck and the sacroiliac joint.
The distal interphalangeal predominant type generally affects the joints nearest to the ends of the fingers and toes, causing sausage fingers or dactylitis and nail abnormalities like ridging or pitting.
Over time, some individuals with distal interphalangeal predominant type may develop severe bone erosions and finger deformities; and this leads to the final type, which is arthritis mutilans.
The extensive bone erosion at the fingers creates a telescopic digit appearance and results in a person having what’s called the opera-glass hand.

Diagnosis4:24–5:02

Diagnosing psoriatic arthritis is challenging, because it resembles rheumatoid arthritis. In addition, having psoriasis and arthritis doesn’t always mean psoriatic arthritis because there are other types of arthritis like osteoarthritis which can develop in individuals with psoriasis.
Blood tests for the antibody rheumatoid factor and anti-citrullinated protein antibodies can help, because they’re commonly seen in rheumatoid arthritis, and are generally absent in psoriatic arthritis.
Also, an X ray can help show joint erosion, and show classic features like the pencil-in-cup radiographic sign. Treatment of pain in mild cases of psoriatic arthritis includes non-steroidal anti-inflammatory drugs.

Treatment5:02–5:52

In more severe cases, immunomodulatory drugs like sulfasalazine and methotrexate can be helpful. If NSAIDs or disease modifying antirheumatic drugs fail, newer drugs called biological response modifiers can also be used.
These include the TNF–inhibitors, such as infliximab, etanercept, and adalimumab, which block the actions of tumor necrosis factor alpha - as well as the IL-12/IL-23 inhibitor ustekinumab, which blocks the actions of the interleukins.
Finally, surgery can be performed to repair damaged hip and knee joints, but spinal surgery is typically considered risky and is rarely performed.
All right, as a quick recap, psoriatic arthritis is an autoimmune process, often associated with the HLA-B27 gene, which causes a T-cell mediated attack of the joints in people with psoriasis.

Review5:52–6:27

There are five different types of psoriatic arthritis, which can be oligoarticular, polyarticular or rheumatoid pattern, spondyloarthritis, distal interphalangeal predominant, and arthritis mutilans.
Treatment includes use of NSAIDS, sulfasalazine, and methotrexate, as well as newer biological response modifiers.