Pseudogout (Calcium Pyrophosphate Dihydrate)
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- Autoinflammatory disease triggered by calcium pyrophosphate dihydrate (CPPD) crystal deposition within joints
- One of many diseases associated with pathologic deposition of crystal; mineralization and ossification
- CPPD crystal deposition = chondrocalcinosis (calcification of hyaline or fibrocartilage), pseudogout, and pyrophosphate arthropathy
- Monosodium urate crystal deposition = gout
- Hydroxyapatite deposition associated with ankylosing spondylitis, osteoarthritis, and vascular calcification
- Suspect pseudogout in arthritis cases with a pattern of joint involvement inconsistent with degenerative joint disease (e.g., metacarpophalangeal joints, wrists).
- Clinical presentation is broad:
- Chronic CPPD crystal deposition may cause a progressive degenerative arthritis in numerous joints:
- Primarily affects the elderly
- Usually involves large joints
- Symptom onset is usually insidious.
- Definitive diagnosis requires the identification of CPPD crystals in synovial fluid.
- System(s) affected: endocrine/metabolic; musculoskeletal
- Synonyms: pseudogout; CPPD; pyrophosphate arthropathy; chondrocalcinosis—when calcification visibly seen within tissues on imaging
- Predominant age: 80% of patients >60 years
- No gender predominance. Men more likely to present acutely; women more likely to present atypically
- Prevalence varies by method of identification (chondrocalcinosis on radiograph vs. CPPD crystals in synovial fluid).
- Chondrocalcinosis is present in 1:10 adults age 60 to 75 years and 1:3 by >80 years; however, only a small percentage develop arthropathy.
- 20–43% prevalence of CPPD crystals in synovial fluid of osteoarthritic joints at time of joint replacement
Etiology and Pathophysiology
- Arthropathy results from an acute autoinflammatory reaction to CPPD crystals in the synovial cavity.
- CPPD crystal deposition occurs in three stages:
- CPPD crystals first develop in the pericellular matrix of the articular cartilage via overproduction of anionic pyrophosphate (PPi).
- PPi binds calcium to form CPPD crystals that are released from cartilage surface eliciting an inflammatory response. Neutrophils engulf CPPD crystals, inducing extracellular trap formation.
- Increased CPPD crystal deposition in and around cartilage causes inflammation and damage. Cartilage degeneration is accelerated through mechanical wear and tear of the joint (2)[C].
Uncommonly seen in familial pattern with autosomal dominant inheritance (<1% of patients); most cases are sporadic. Mutation in ANKH gene increases risk for calcium crystal formation.
- Advanced age
- Joint trauma
- CPPD may occur as a complication in patients hospitalized for other medical and surgical illnesses.
Colchicine 0.6 mg BID may be used prophylactically to reduce frequency of episodes in recurrent CPPD.
Commonly Associated Conditions
- Hemochromatosis; ochronosis
- Wilson disease
- Familial hypocalciuric hypercalcemia
- X-linked hypophosphatemic rickets