Pseudogout
Acute calcium pyrophosphate crystal arthritis (pseudogout) is a sudden inflammatory monoarthritis or oligoarthritis of the knee or wrist caused by shedding of rhomboid, positively birefringent calcium pyrophosphate crystals into the joint. First-line treatment is joint aspiration with intra-articular glucocorticoid injection, plus NSAIDs or colchicine; no therapy dissolves the crystals.
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What this article covers
- Overview
Definition: acute calcium pyrophosphate (CPP) crystal arthritis, or pseudogout, is an inflammatory monoarthritis or oligoarthritis from shedding of CPP crystals from articular cartilage.
- Epidemiology
Age-dependent prevalence: chondrocalcinosis risk roughly doubles each decade after age 60, and nearly half of patients in their 80s have CPP deposits on plain radiographs.
- Risk factors
Advancing age: the dominant risk factor, with prevalence rising steeply after age 60.
- Pathophysiology
Crystal formation: inorganic pyrophosphate from chondrocytes combines with calcium in cartilage matrix to precipitate CPP crystals; low magnesium, excess calcium, and low alkaline phosphatase in synovial fluid favor formation.
- Clinical features
Joint distribution: the knee and wrist are the most commonly affected joints; shoulders, elbows, ankles, and intervertebral disks can also be involved, and more than one joint is uncommonly affected at once.
- Differential diagnosis
Gout: classically targets the first metatarsophalangeal joint rather than the knee or wrist; synovial fluid shows negatively birefringent, needle-shaped monosodium urate crystals rather than…
- Diagnosis
How the diagnosis is established: definitive diagnosis requires identification of CPP crystals, with leukocytes, in synovial fluid by arthrocentesis; the crystals are rhomboid or rod-shaped and…
- Management
First, aspirate the joint. Arthrocentesis is both diagnostic and therapeutic, decompressing the effusion and confirming CPP crystals; send fluid for Gram stain and culture at the same time to exclude coexisting infection.
- Complications
Recurrent flares: untreated or inadequately prophylaxed disease recurs, with flares persisting weeks to months.
- Prognosis
Acute attacks: most flares resolve within about 1 week with treatment; untreated attacks can persist weeks to months.
- Prevention
Prophylaxis threshold: start colchicine 0.6 mg once or twice daily, or a daily low-dose NSAID with gastrointestinal protection, after 3 or more attacks in a year.
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