Gout, Pseudogout, Ankylosing Spondylitis, & Other Arthitides for USMLE Step 3 / COMLEX-USA Level 3

• Definition: A disorder of uric acid metabolism characterized by recurrent attacks of acute arthritis due to monosodium urate crystal deposition.

• Hyperuricemia: Overproduction or underexcretion of uric acid.
• Crystal-Induced Inflammation: Monosodium urate crystals activate inflammatory mediators.

• Acute Gouty Arthritis: Sudden, severe joint pain, erythema, and swelling, typically at the 1st metatarsophalangeal (MTP) joint (podagra).
• Chronic Gout: Tophi (subcutaneous urate deposits), chronic joint deformities, and nephrolithiasis.

• Synovial Fluid Analysis: Needle-shaped, negatively birefringent crystals under polarized light microscopy.
• Serum Uric Acid: Often elevated but not definitive.

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• Definition: An arthritic condition due to deposition of calcium pyrophosphate crystals in the joints.

• Crystal Deposition: Calcium pyrophosphate crystals deposit in cartilage, triggering inflammation and joint damage.

• Acute CPPD Arthritis: Pain, redness, and swelling in large joints (e.g., knee).
• Chronic CPPD: Mimics osteoarthritis or rheumatoid arthritis with progressive joint damage.

• Synovial Fluid Analysis: Rhomboid-shaped, positively birefringent crystals under polarized light.
• Imaging: Chondrocalcinosis (cartilage calcification).

Gout Pseudogout

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• Definition: An inflammatory arthritis occurring after an infection (genitourinary or gastrointestinal).

• Immune-Mediated Response: Post-infectious inflammatory response; often triggered by pathogens such as Chlamydia, Salmonella, Shigella.

• Triad: Arthritis, conjunctivitis/uveitis, and urethritis ("can't see, can't pee, can't climb a tree").
• Enthesitis: Pain at tendon or ligament insertions.

• Clinical Diagnosis: Based on symptoms and recent infection history.
• HLA-B27: Associated with some cases but not diagnostic.

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• Definition: A chronic inflammatory disease primarily involving the spine and sacroiliac joints, leading to ankylosis and reduced mobility.

• HLA-B27 Association: Strong genetic predisposition linked to HLA-B27 allele.
• Chronic Inflammation: Results in spinal and sacroiliac joint fusion.

• Back Pain and Stiffness: Gradual onset, morning stiffness, improves with exercise.
• Extra-Articular Manifestations: Uveitis, aortic insufficiency, and inflammatory bowel disease.

• Imaging: "Bamboo spine" due to vertebral fusion on X-ray.
• Laboratory Studies: Elevated ESR/CRP, HLA-B27 testing.

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• Definition: An inflammatory arthritis associated with psoriasis, affecting both peripheral and axial joints.

• Immune-Mediated Inflammation: Affects skin (psoriatic plaques) and joints.

• Joint Involvement: Asymmetric oligoarthritis, DIP joint involvement, dactylitis ("sausage digits"), and nail pitting.
• Variable Presentation: Patterns may mimic rheumatoid arthritis or spondyloarthritis.

• Clinical Features: History of psoriasis and characteristic joint involvement.
• Radiographic Findings: "Pencil-in-cup" deformity and joint erosions.

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• Definition: Infection within the joint space, a medical emergency requiring rapid intervention.

• Bacterial Joint Infection: Commonly caused by Staphylococcus aureus; Neisseria gonorrhoeae in sexually active individuals.

• Rapid-Onset Monoarthritis: Acute pain, swelling, fever, and limited range of motion in large joints (e.g., knee, hip).
• Systemic Symptoms: Fever and malaise.

• Joint Aspiration: Purulent fluid with high WBC (>50,000 cells/mm³), positive culture/Gram stain.

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• Gout vs. Pseudogout: Differentiated by crystal type (urate vs. calcium pyrophosphate) and birefringence on microscopy.
• Seronegative Spondyloarthropathies: Group includes ankylosing spondylitis, reactive arthritis, and psoriatic arthritis, often linked with HLA-B27.
• Septic Arthritis: Requires prompt diagnosis and antibiotic therapy to prevent joint damage; suspect in acute monoarthritis with systemic symptoms.
• Pattern Recognition: Understanding characteristic clinical patterns and extra-articular manifestations is crucial for diagnosis and differentiation.