Musculoskeletal

Pseudogout (CPPD)

Acute calcium pyrophosphate crystal arthritis, usually affecting an older person's knee or wrist; confirm the crystal when needed, exclude septic arthritis, and treat the flare without confusing it with urate-driven gout.

In a nutshell

Pseudogout is acute CPP crystal arthritis within the wider CPPD spectrum. It commonly affects an older person's knee or wrist, but a hot joint may be septic. Aspirate when uncertain: CPP crystals are rhomboid and weakly positively birefringent. Treat the flare with an appropriately selected anti-inflammatory; allopurinol is not a CPPD treatment.

Classic presentation

An older person develops an acute red, hot, swollen and very painful knee or wrist, often with chondrocalcinosis on X-ray, but aspiration is needed when infection or the crystal identity is uncertain.

Key points

CPPD includes asymptomatic chondrocalcinosis, acute CPP crystal arthritis and chronic CPPD-related joint disease.
The acute presentation can mimic gout and septic arthritis; fever does not distinguish them safely.
CPP crystals are rhomboid and weakly positively birefringent; urate crystals are needle-shaped and negatively birefringent.
Chondrocalcinosis supports CPPD but does not prove that an acute hot joint is non-infective.
Treat the flare with an NSAID, colchicine or corticosteroid according to comorbidity and medicine safety; aspiration and local steroid injection may help a single large joint after infection is excluded.
Do not use allopurinol for CPPD; there is no established urate-lowering equivalent.
Consider targeted metabolic assessment for early-onset, florid, recurrent or atypical disease.
Frequent, refractory or chronic inflammatory disease warrants rheumatology-led planning.

First-line investigation

Synovial-fluid aspiration for CPP crystals, Gram stain and culture when infection or diagnostic uncertainty is present.

Management

Recognise the hot joint and rule out sepsis

Assess systemic illness and infection risk; aspirate for crystals, Gram stain and culture when the diagnosis is uncertain or infection is possible.^3,4
Do not let a radiograph showing chondrocalcinosis or a previous CPPD diagnosis prevent urgent septic-arthritis assessment.^3,4

Treat acute inflammation safely

Select an NSAID, colchicine or corticosteroid after considering renal, gastrointestinal, cardiovascular and interaction risks; check the BNF.^5,6,7,2
For a single large joint, aspiration and local steroid injection may be sufficient after infection is excluded and when performed by appropriate expertise.²

Support recovery and avoid the wrong long-term drug

Use temporary rest and cool packs, then encourage gradual mobilisation as pain settles; review function and coexisting osteoarthritis.²
Do not start allopurinol for CPPD; it is a gout treatment and does not lower calcium pyrophosphate crystal burden.^3,1

Investigate atypical and recurrent disease

Consider targeted assessment for associated metabolic conditions in early-onset, florid, recurrent or atypical CPPD, with senior or rheumatology input.²
For frequent attacks or chronic inflammatory CPPD, rheumatology may consider prophylactic or disease-directed therapy after an individual risk-benefit review.^2,5

Confirm improvement and safety-net

Explain the confirmed or working diagnosis, medicine risks and recurrence plan; review mobility, osteoarthritis and the need for specialist follow-up.^1,2
Seek urgent review for fever, systemic illness, a worsening joint or failure to improve because septic arthritis may coexist or have been missed.^3,4

Exam traps

Do not diagnose pseudogout from age, knee pain or chondrocalcinosis alone.
CPP crystals are weakly positively birefringent rhomboids, not negatively birefringent urate needles.
A crystal finding does not exclude septic arthritis.
Allopurinol treats gout, not CPPD.
Do not order or promise a universal metabolic screen or prophylactic regimen without considering age, phenotype, comorbidity and specialist advice.

Illustrations

Chondrocalcinosis on knee X-rayRadiograph of the knee showing linear calcification of the meniscal and articular cartilage (chondrocalcinosis), a supportive feature of calcium pyrophosphate deposition.Taokinesis (Pixabay profile), annotated by Mikael Haggstrom, Wikimedia Commons · CC0

Calcium pyrophosphate crystals under polarised lightMicroscopy image of rhomboid, weakly positively birefringent calcium pyrophosphate crystals in synovial fluid, contrasted with the needle-shaped negatively birefringent urate crystals of gout.Mikael Haggstrom, M.D., Wikimedia Commons · CC0

Key sources

This page is exam revision material, not medical advice, and must not be used for patient care. Always check drug doses against the BNF and current guidance. Full disclaimer.