Gout, Pseudogout, Ankylosing Spondylitis, & Other Arthitides for USMLE Step 2 / COMLEX-USA Level 2

• Definition: A disorder characterized by recurrent attacks of acute arthritis due to monosodium urate crystal deposition in joints, leading to inflammation.

• Hyperuricemia: Due to overproduction or underexcretion of uric acid.
• Crystals and Inflammation: Monosodium urate crystals trigger neutrophil-mediated inflammation.

• Acute Gout Attack: Rapid onset of severe pain, redness, and swelling, typically affecting the 1st metatarsophalangeal (MTP) joint (podagra).
• Chronic Gout: Tophi formation, chronic arthritis, and possible renal complications (e.g., nephrolithiasis).

• Arthrocentesis: Needle-shaped, negatively birefringent crystals under polarized light microscopy.
• Serum Uric Acid: Elevated levels support diagnosis but are not definitive.

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• Definition: A form of arthritis caused by calcium pyrophosphate crystal deposition in joints.

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

• Acute Arthritis: Affects larger joints (knee, wrist), presenting with pain, swelling, and warmth.
• Chronic CPPD: Can mimic osteoarthritis with progressive joint degeneration.

• Arthrocentesis: Rhomboid-shaped, positively birefringent crystals under polarized light microscopy.
• Imaging: Chondrocalcinosis visible on radiographs.

Gout Pseudogout

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• Definition: An autoimmune arthritis following an infection (GI or genitourinary).

• Immune-Mediated Response: Often triggered by pathogens such as Chlamydia, Salmonella, Shigella, Yersinia, or Campylobacter.

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

• Clinical Diagnosis: Based on recent infection and characteristic symptoms.
• HLA-B27: Present in some patients but not specific.

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

• Genetic Association: Strongly associated with HLA-B27.
• Inflammation and Ossification: Involves sacroiliac joints, spine, and extraspinal entheses.

• Low Back Pain: Insidious onset, improves with activity, with prolonged morning stiffness.
• Extra-Articular Manifestations: Uveitis, aortic regurgitation, and inflammatory bowel disease.

• Radiographic Findings: Sacroiliitis and "bamboo spine" due to vertebral fusion.
• Laboratory Studies: Elevated ESR/CRP, HLA-B27.

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• Definition: Inflammatory arthritis associated with psoriasis.

• Autoimmune Inflammation: Affects both skin and joints.

• Variable Presentation: Asymmetric oligoarthritis, DIP joint involvement, dactylitis ("sausage digits"), and nail changes.
• Patterns of Joint Involvement: Can resemble rheumatoid arthritis or ankylosing spondylitis.

• Clinical Assessment: Based on psoriatic skin lesions and joint symptoms.
• Radiography: "Pencil-in-cup" deformity seen in advanced disease.

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• Definition: Bacterial infection of the joint, a medical emergency.

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

• Acute Joint Pain and Swelling: Fever, joint warmth, erythema, and reduced range of motion.
• Monoarticular Presentation: Commonly affects the knee, hip, or other large joints.

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

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• Crystal Arthropathies: Differentiate gout (urate crystals, negatively birefringent) from pseudogout (calcium pyrophosphate crystals, positively birefringent).
• Seronegative Spondyloarthropathies: Includes ankylosing spondylitis, reactive arthritis, and psoriatic arthritis; often associated with HLA-B27.
• Septic Arthritis: Requires prompt diagnosis and treatment to prevent joint damage; suspect in any acutely swollen joint with systemic symptoms.
• Characteristic Presentations: Recognize key clinical features and patterns for timely diagnosis and differentiation among these arthritic conditions.