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A 20-year-old man presents to the office because of joint pain, particularly in his fingers. Physical examination shows significant swelling of his fingers and pitting in his fingernails. He is most tender to palpation across his DIP joints. Three months ago, he visited the office because of a rash, shown below. Besides some itching, he denied any other symptoms. Topical treatments helped with the itching. Which of the following haplotypes is most commonly associated with this condition?
Content Reviewers:Rishi Desai, MD, MPH
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.
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.
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.
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.
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.
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.