Gout, Pseudogout, Ankylosing Spondylitis, & Other Arthitides for the Physician Assistant Licensing Exam
Gout
- Definition: A metabolic disorder characterized by monosodium urate crystal deposition in joints, leading to acute inflammatory arthritis.
Pathophysiology
- Hyperuricemia: Due to overproduction or underexcretion of uric acid.
- Crystal-Induced Inflammation: Uric acid crystals trigger neutrophil-mediated inflammation in the joints.
Clinical Features
- Acute Gouty Arthritis: Sudden, intense joint pain with erythema and swelling, often affecting the 1st MTP joint (podagra).
- Chronic Gout: Tophi (urate deposits in soft tissues), recurrent attacks, and potential renal complications like nephrolithiasis.
Diagnosis
- Joint Aspiration: Needle-shaped, negatively birefringent crystals under polarized light.
- Serum Uric Acid: Elevated but not always during acute flare-ups.
- --
Pseudogout (Calcium Pyrophosphate Deposition Disease - CPPD)
- Definition: Arthritis caused by calcium pyrophosphate crystal deposition in joints, also known as CPPD.
Pathophysiology
- Crystal Formation: Calcium pyrophosphate crystals deposit in cartilage, leading to inflammation and chondrocalcinosis.
Clinical Features
- Acute Pseudogout: Sudden joint pain, swelling, and warmth, often in the knee or wrist.
- Chronic CPPD: Progressive joint degeneration similar to osteoarthritis or rheumatoid arthritis.
Diagnosis
- Joint Aspiration: Rhomboid-shaped, positively birefringent crystals.
- Imaging: Chondrocalcinosis seen on radiographs.
Urate and CPPD Histological Image References
Gout
Pseudogout
- --
Reactive Arthritis
- Definition: A sterile arthritis occurring after a gastrointestinal or genitourinary infection.
Pathophysiology
- Immune-Mediated Response: Post-infectious autoimmunity, often triggered by pathogens such as Chlamydia, Salmonella, or Shigella.
Clinical Features
- Classic Triad: Arthritis, conjunctivitis, and urethritis ("can't see, can't pee, can't climb a tree").
- Enthesitis: Inflammation at sites where tendons or ligaments insert into bone.
Diagnosis
- Clinical Diagnosis: Based on history of infection and characteristic symptoms.
- HLA-B27 Testing: May be positive but is not required for diagnosis.
- --
Ankylosing Spondylitis (AS)
- Definition: A chronic inflammatory disease primarily affecting the axial skeleton and sacroiliac joints.
Pathophysiology
- Genetic Predisposition: Strongly associated with HLA-B27 antigen.
- Chronic Inflammation and Fusion: Leads to vertebral fusion and reduced spinal mobility.
Clinical Features
- Low Back Pain and Stiffness: Gradual onset, worse in the morning, improves with activity.
- Extra-Articular Manifestations: Uveitis, cardiovascular involvement (e.g., aortic regurgitation), and pulmonary fibrosis.
Diagnosis
- Imaging: Sacroiliitis on X-ray; "bamboo spine" in advanced disease.
- Laboratory Tests: Elevated ESR/CRP, positive HLA-B27.
- --
Psoriatic Arthritis (PsA)
- Definition: An inflammatory arthritis associated with psoriasis, involving peripheral and axial joints.
Pathophysiology
- Autoimmune Inflammation: Affects both skin and joints, leading to joint damage.
Clinical Features
- Joint Involvement: Asymmetric oligoarthritis, dactylitis ("sausage digits"), DIP joint involvement, and nail pitting.
- Variable Presentation: Patterns can resemble rheumatoid arthritis or ankylosing spondylitis.
Diagnosis
- Clinical Correlation: Psoriasis with characteristic joint findings.
- Imaging: "Pencil-in-cup" deformities on X-ray.
- --
Septic Arthritis
- Definition: A bacterial infection of the joint space that requires immediate intervention.
Pathophysiology
- Infectious Agents: Typically caused by Staphylococcus aureus; consider Neisseria gonorrhoeae in sexually active individuals.
Clinical Features
- Acute Onset of Monoarticular Arthritis: Rapid onset of joint pain, swelling, warmth, and fever, commonly affecting a large joint (e.g., knee).
- Systemic Symptoms: Fever, chills, and malaise.
Diagnosis
- Joint Aspiration: Purulent fluid with high WBC count (>50,000 cells/mm³), and positive Gram stain/culture.
- --
Essential Points
- Gout vs. Pseudogout: Differentiation based on crystal type; gout has monosodium urate crystals (negatively birefringent), pseudogout has calcium pyrophosphate crystals (positively birefringent).
- Seronegative Spondyloarthropathies: Include ankylosing spondylitis, reactive arthritis, and psoriatic arthritis, often associated with HLA-B27.
- Septic Arthritis: A medical emergency; requires immediate diagnosis and treatment with antibiotics.
- Recognize Patterns: Key to distinguishing between these conditions is identifying specific clinical patterns, triggers, and associated features (e.g., skin findings in PsA).