Arthritis - crystal-associated, such as gout and pseudogout
Description
- Arthritis caused by crystal deposition in and around joints -> NLRP3 inflammasome -> IL-1beta -> acute neutrophilic synovitis
| Gout | CPPD (pseudogout) | Basic calcium phosphate | |
|---|---|---|---|
| Crystal | Monosodium urate | Calcium pyrophosphate dihydrate | Hydroxyapatite |
| Shape | Needle | Rhomboid / rod | Non-birefringent, too small to see |
| Birefringence | Strong NEGATIVE (yellow when parallel to the compensator) | Weak POSITIVE (blue when parallel) | None |
| Classic joint | 1st MTP (podagra) | Knee, wrist | Shoulder (Milwaukee), calcific tendinitis |
| Radiology | Punched-out erosions, overhanging edge | Chondrocalcinosis | Periarticular calcification |
- Mnemonic: ABC - Acute gout is negative needle; CPPD is the other one
Gout phases
- Asymptomatic hyperuricaemia -> acute flare -> intercritical (asymptomatic) -> chronic tophaceous gout
- Flare: peaks within 12-24 h, exquisite pain, erythema, resolves in 7-14 days untreated
- *Not all hyperuricaemia is gout; not all gout is hyperuricaemic at the time of the flare*
CPPD phenotypes
- Asymptomatic chondrocalcinosis - commonest
- Acute CPP crystal arthritis (pseudogout)
- Chronic CPP inflammatory arthritis - RA mimic
- OA with CPPD - unusual distribution: MCPs, wrists, shoulders, elbows
- Crowned dens syndrome - CPPD around the odontoid -> acute neck pain, fever, inc CRP; meningitis and GCA mimic
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