Psoriatic arthritis

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Psoriatic arthritis



Psoriatic arthritis


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USMLE® Step 1 questions

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Psoriatic arthritis

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USMLE® Step 1 style questions USMLE

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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.  

Retrieved fromWikimedia Commons  

Which of the following clinical findings is associated with this patient’s condition?  

External References

First Aid








Patches (skin)

psoriatic arthritis p. 479

Psoriatic arthritis p. 479

HLA-B25 and p. 98

leflunomide for p. 499

psoriasis and p. 489


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.


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.


  1. "Robbins Basic Pathology" Elsevier (2017)
  2. "Harrison's Principles of Internal Medicine, Twentieth Edition (Vol.1 & Vol.2)" McGraw-Hill Education / Medical (2018)
  3. "Pathophysiology of Disease: An Introduction to Clinical Medicine 8E" McGraw-Hill Education / Medical (2018)
  4. "CURRENT Medical Diagnosis and Treatment 2020" McGraw-Hill Education / Medical (2019)
  5. "Psoriatic arthritis: from pathogenesis to therapy" Arthritis Research & Therapy (2009)
  6. "Pathogenetic Overview of Psoriatic Disease" The Journal of Rheumatology Supplement (2012)

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