Pseudogout (aka CPPD)
calcium pyrophosphate deposition disease (pseudogout)
Demographic
- The disease is quite different than gout (which is why pseudogout is really a misnomer) – it tends to occur in older individuals (older than 50 yo and most commonly over 80 yo (note that gout tends to occur in the 40s or 50s in men and later on in women).
Rhomboid-shaped, positive birefringence
- Polarized light microscopy reveals rhomboid-shaped crystals with positive birefringence – they are blue in parallel to the slow wave of light (unlike gout crystals, which are needle-shaped and have negative birefringence).
Pathogenesis
- The disease involves cartilaginous or synovial release of calcium pyrophosphate crystals into the joint space, most commonly the knee (whereas in gout it's most often the MTP joint).
- This deposition produces an inflammatory cascade. There is cartilaginous calcification on X-Ray (chondrocalcinosis).
Treatment
- Similar to gout, we use NSAIDs (eg, indomethacin), as well as intra-articular glucocorticoid injections or oral prednisone to reduce inflammation. Typically, the response is less dramatic than in gout and, therefore, requires a longer duration of therapy.
"Blue P's"
- We can use the mnemonic the Blue P's to help us remember some highlights of the disease:
- Pseudogout has calcium Pyrophosphate deposition that exhibit Positive birefringence – they are blue when in parallel to the slow wave of polarized light.
Image Sources
Urate and CPPD Histological Image References
Gout
Pseudogout