What is Psoriatic Arthritis

Psoriatic arthritis is a chronic autoimmune disease that causes inflammation and pain, with consequent functional deficits in the joints. It occurs in people with cutaneous psoriasis, a chronic skin disease in which scales appear that may itch and/or bleed, producing nail lesions in approximately one third of cases.

It affects both men and women and usually develops between 30 and 50 years of age. Only 10-30% of people with psoriasis will develop psoriatic arthritis.

The main lesion of psoriatic arthritis is inflammation of the enthesis (the junction between ligament or tendon and the bony cortex). This inflammation can produce enthesitis (inflammation of the enthesis), tendinitis (inflammation of the tendon) or dactylitis (inflammation of the flexor and extensor tendon and adjacent soft tissues). By extension, the inflammatory process can affect the articular synovial membrane producing synovitis.

Psoriatic arthritis is included in the group of spondyloarthropathies, like ankylosing spondylitis or reactive arthritis, as it can affect the spine in the form of pain, inflammation and in very aggressive cases, fusion of the spine or the sacroiliac joint.

How is it possible for psoriasis and arthritis to coexist?

Both psoriasis and psoriatic arthritis have a number of common genetic susceptibilities that cause an abnormal functioning of the immune system, which under appropriate environmental conditions results in the production of inflammation of the skin or joints.

The presence of the HLAB27 gene is the most important and well known, since it encodes a series of proteins on the surface of lymphocytes that when they function abnormally trigger the inflammatory mechanism.

There are other diseases that share this association to HLAB27, such as Crohn’s disease, ulcerative colitis or uveitis; that is why a person diagnosed with one of these diseases is more likely to associate another of the same group.

Psoriasis or arthritis, which comes first?

Approximately 70% of patients with psoriatic arthritis initially present with cutaneous psoriasis, especially if there is nail involvement. The reverse case (presenting with arthritis without skin psoriasis) occurs in only 15% of cases. However, in these cases the diagnosis is complicated, given the absence of psoriasis, so we have to resort to the presence of a family history of psoriasis and it is usually diagnosed as seronegative arthritis, or as “possible psoriatic arthritis”, subsequently adapting the diagnosis depending on the clinical course.

This does not mean that it cannot be treated with antirheumatics and remission can be achieved. Rheumatology is a young specialty, and there are still unknowns to be resolved. It is the individual’s genetics that determine when and how the disease will develop, so it is currently impossible to know how psoriatic arthritis will debut.

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Common symptoms of psoriatic arthritis

  • Arthritis/synovitis: the presence of pain and inflammation in one or more joints.
  • Dactylitis: swelling of fingers or toes, with a “sausage” appearance due to simultaneous inflammation of flexor and extensor tendons, synovial membrane involvement and soft tissue inflammation.
  • Inflammatory tendinitis/entesitis: either in the form of inflammation of the tendons of the hands and feet, or in the Achilles tendon.
  • Inflammatory lumbago: axial involvement is not obligatory, but when it appears it is in the form of pain that worsens with rest and improves with movement, basically at the dorsal or lumbar level.
  • Sacroiliitis: inflammation of the sacroiliac joint, located in the buttock. It usually affects unilaterally (only on one side).
  • Onychopathy: psoriatic involvement of the nails, with the classic “oil stain” image.

Treatment

The goal of psoriatic arthritis treatment is to reduce pain and inflammation, control skin psoriasis, and prevent joint damage (bone erosions), restoring the patient’s quality of life to a state similar to that prior to diagnosis. Psoriatic arthritis currently has no curative treatment, which does not mean that there is no treatment at all.

The first line of treatment is treatment with non-steroidal anti-inflammatory drugs (NSAIDs) and corticosteroids (oral or infiltrated in entheses or joints), especially in cases with peripheral involvement or enthesitis/dactylitis.

In cases where many joints are affected and psoriasis is present, treatment is initiated with antirheumatic drugs, the so-called DMARDs (disease-modifying antirheumatic drugs). In other words, it is no longer a matter of “deflating”, but of preventing the inflammatory process from appearing. These are usually very safe chronic medications such as methotrexate or salazopyrin, among others.

In those cases in which the disease is not controlled with DMARDs, or in some cases of axial involvement, it is necessary to treat the patient with the so-called biologic therapies: a category of targeted DMARDs that act at different points of the inflammatory cascade, blocking different molecules involved in the inflammatory process: TNF-alpha blockers (adalimumab, golimumab), interleukin 12/23 inhibitors (ustekinumab), interleukin 17-A inhibitors (secukinumab and ixekizumab) and phosphodiesterase-4 inhibitors (apremilast). Each of these treatments should be instituted by rheumatologists, following subsequent controls in consultation.