Rheumatology · Crystal Arthropathy
The facts most likely to be tested
The gold standard for diagnosis is synovial fluid analysis showing needle-shaped, negatively birefringent crystals.
Acute gouty arthritis classically presents as podagra, which is intense pain and inflammation of the first metatarsophalangeal joint.
First-line pharmacotherapy for an acute gout flare includes NSAIDs (e.g., indomethacin), colchicine, or corticosteroids.
Chronic management to lower serum uric acid levels is indicated for patients with recurrent flares, tophi, or gouty nephropathy.
Allopurinol is the first-line xanthine oxidase inhibitor used for long-term urate-lowering therapy.
Prophylactic anti-inflammatory therapy with low-dose colchicine or NSAIDs is required when initiating urate-lowering therapy to prevent acute flare precipitation.
Radiographic findings in chronic, untreated gout include punched-out erosions with overhanging edges (rat-bite erosions).
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A 58-year-old male presents to the emergency department with severe pain and swelling in his right big toe that began overnight. He reports a history of hypertension and consumes a diet high in red meat and beer. Physical examination reveals an erythematous, edematous, and exquisitely tender first metatarsophalangeal joint. He is afebrile, and his white blood cell count is mildly elevated. Arthrocentesis of the joint is performed.
What is the most likely finding on synovial fluid analysis?
Needle-shaped, negatively birefringent crystals
The patient's presentation of podagra is classic for acute gout, which is confirmed by the presence of needle-shaped, negatively birefringent crystals under polarized light microscopy.
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High yield triage
Etiology / Epidemiology
Affects middle-aged men and postmenopausal women; driven by hyperuricemia (>6.8 mg/dL) and purine metabolism.
Clinical Manifestations
Acute, monoarticular, inflammatory arthritis; podagra is the first metatarsophalangeal joint hallmark.
Diagnosis
Arthrocentesis with negatively birefringent needle-shaped crystals is the gold standard.
Treatment
NSAIDs (e.g., indomethacin) are first-line for acute flares; avoid aspirin as it alters urate excretion.
Prognosis
Chronic disease leads to tophi formation and urate nephropathy; requires long-term allopurinol.
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Epidemiology & Etiology
Prevalence peaks in males 30-50 years old due to higher baseline uric acid levels. Primary causes include purine-rich diet, alcohol (especially beer), and medications like thiazide diuretics. Secondary causes involve high cell turnover states like tumor lysis syndrome.
Pertinent Anatomy
The first metatarsophalangeal joint is the most common site due to lower temperatures, which favor crystal precipitation. Urate crystals also deposit in the helix of the ear, olecranon bursa, and Achilles tendon.
Pathophysiology
Hyperuricemia leads to the precipitation of monosodium urate crystals within the synovial fluid. These crystals trigger an intense inflammatory response via the NLRP3 inflammasome, recruiting neutrophils to the joint space. Recurrent episodes lead to chronic synovitis and the development of tophi.
Clinical Manifestations
Patients present with sudden onset, severe joint pain, erythema, and swelling, often peaking within 24 hours. Podagra is the classic presentation of the first MTP joint. Septic arthritis must always be ruled out via joint aspiration if the patient is febrile or systemic symptoms are present.
Diagnosis
Arthrocentesis is the gold standard to confirm diagnosis and exclude infection. Synovial fluid analysis reveals negatively birefringent needle-shaped crystals. Serum uric acid levels may be normal during an acute flare and are not diagnostic.
Treatment
Acute management utilizes NSAIDs, colchicine, or corticosteroids. Colchicine is most effective if started within 24 hours of symptom onset. Chronic management involves allopurinol to lower serum urate levels to <6.0 mg/dL. Do not initiate urate-lowering therapy during an acute flare.
Prognosis
Untreated gout progresses to chronic tophaceous gout, causing joint destruction and deformity. Long-term complications include nephrolithiasis and chronic kidney disease. Patients require monitoring of serum creatinine and uric acid levels.
Differential Diagnosis
Pseudogout: positively birefringent rhomboid crystals
Septic arthritis: positive synovial fluid culture
Cellulitis: absence of joint space involvement
Trauma: history of injury and negative crystals
Rheumatoid arthritis: symmetric, polyarticular involvement