USMLE® Step 1 style questions USMLE
A 45-year-old woman presents to her primary care physician's office for evaluation of pain and stiffness in fingers and low back for six months. The pain is worse early in the morning and gradually improves over the course of the day. She also has soreness of the heels bilaterally. The patient has been taking acetaminophen with only partial relief. Past medical history includes myocardial infarction with stent placement one year ago. Physical examination shows point tenderness over the bilateral Achilles tendons, as well as effusion and joint line tenderness of 3rd and 4th distal interphalangeal joints of the bilateral hands. The patient’s left thumb is demonstrated below.
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Which of the following clinical findings is associated with this patient’s condition?
Psoriatic arthritis exam links
Content Reviewers:Rishi Desai, MD, MPH
Contributors:Tanner Marshall, MS, Sam Gillespie, BSc, Antonella Melani, MD
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.
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.
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.
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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