Gout, Pseudogout, Ankylosing Spondylitis, & Other Arthitides for USMLE Step 1 / COMLEX-USA Level 1

• Definition: A metabolic disorder characterized by hyperuricemia, leading to the deposition of monosodium urate crystals in joints, causing acute inflammatory arthritis.

• Uric Acid Overproduction or Underexcretion: Elevated uric acid levels result from increased production (purine metabolism) or decreased renal excretion.
• Crystal Formation: Monosodium urate crystals precipitate in joints, triggering an inflammatory response.

• Acute Attacks: Sudden onset of severe joint pain, swelling, and erythema, most commonly affecting the 1st metatarsophalangeal (MTP) joint (podagra).
• Chronic Gout: Tophi (nodules of urate crystals), chronic joint deformity, and renal complications like uric acid nephrolithiasis.

• Joint Aspiration: Needle-shaped, negatively birefringent crystals under polarized light microscopy.
• Serum Uric Acid Levels: May be elevated but not definitive for diagnosis.

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• Definition: A type of arthritis caused by the deposition of calcium pyrophosphate dihydrate crystals in joints.

• Crystal Deposition: Calcium pyrophosphate crystals deposit in the joint cartilage, leading to chondrocalcinosis and inflammation.

• Acute Arthritis: Sudden joint pain, swelling, and warmth, often involving the knee, wrist, or ankle.
• Chronic CPPD: Mimics osteoarthritis or rheumatoid arthritis, presenting with progressive joint degeneration.

• Joint Aspiration: Rhomboid-shaped, positively birefringent crystals under polarized light microscopy.
• Radiography: Chondrocalcinosis (cartilage calcification).

Gout Pseudogout

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• Definition: An autoimmune arthritis that occurs after an infection (typically genitourinary or gastrointestinal).

• Post-Infectious Autoimmune Response: Triggered by infections like Chlamydia, Shigella, Salmonella, Campylobacter, or Yersinia.

• Classic Triad: "Can't see, can't pee, can't climb a tree" – conjunctivitis/uveitis, urethritis, and arthritis (asymmetric, oligoarticular).
• Enthesitis: Inflammation at tendon or ligament insertions.

• Clinical Diagnosis: Based on symptoms and history of recent infection.
• HLA-B27 Association: Seen in some cases but not diagnostic.

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• Definition: A chronic inflammatory disease primarily affecting the axial skeleton, leading to progressive stiffness and fusion of the spine.

• HLA-B27 Genetic Association: Strong link with HLA-B27 allele, contributing to immune-mediated inflammation of joints.

• Low Back Pain and Stiffness: Insidious onset, improves with exercise but not rest, with morning stiffness.
• Extra-Articular Manifestations: Uveitis, aortic regurgitation, and inflammatory bowel disease.

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

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• Definition: An inflammatory arthritis associated with psoriasis.

• Immune-Mediated Inflammation: Involves both skin (psoriasis) and joint inflammation.

• Asymmetric Oligoarthritis: May involve the DIP joints, dactylitis ("sausage digits"), and nail pitting.
• Variable Presentation: Can present similarly to rheumatoid arthritis or ankylosing spondylitis.

• Clinical Diagnosis: Based on history of psoriasis, joint symptoms, and imaging findings.
• Radiographic Features: "Pencil-in-cup" deformity of DIP joints.

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• Definition: A bacterial infection of the joint space, often a medical emergency.

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

• Acute Onset: Joint pain, swelling, warmth, and fever.
• Monoarticular Arthritis: Usually affects the knee, hip, shoulder, or other large joints.

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

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• Gout vs. Pseudogout: Different crystals (urate vs. calcium pyrophosphate) and birefringence on microscopy.
• Seronegative Spondyloarthropathies: Includes ankylosing spondylitis, reactive arthritis, and psoriatic arthritis – often associated with HLA-B27.
• Septic Arthritis: Requires rapid diagnosis and treatment with antibiotics and joint drainage to prevent joint destruction.
• Clinical Patterns and Associations: Recognize the characteristic clinical features and extra-articular manifestations of each condition for diagnosis and differentiation.