Most joints with pseudogout deposits revealed by x-ray do not cause any pain. When painful attacks do occur, however, pseudogout may manifest itself in ways similar to a variety of other disorders, such as:

• Gout. It is difficult to clinically differentiate between gout and pseudogout. Because gout and pseudogout crystals are composed differently, it must be established which crystal type is causing the joint inflammation. Crystal deposits associated with pseudogout are made primarily of calcium, unlike gout crystals, which are made of uric acid. Furthermore, attacks of gout typically occur in joints of the toes and feet, whereas pseudogout typically occurs in the knees.

Awareness of these patterns alone is insufficient in making a distinction between gout and pseudogout; further testing is required. Usually, the only difference is the type of crystal in the joint. Pseudogout crystals extracted in an arthrocentesis are positively birefringent (able to split a ray of light in two) under a polarized light microscope, but gout crystals are negatively birefringent. Trauma, surgery or illness may cause attacks of gout, pseudogout or a combination of the two.

• Osteoarthritis. Many people with pseudogout exhibit degeneration of one or more joints in ways similar to osteoarthritis (deterioration of cartilage in the joints). Calcium pyrophosphate dihydrate (CPPD) crystal deposits, which cause attacks of pseudogout, are often present in osteoarthritic joints. CPPD crystal deposits are thought to play a role in the progression of osteoarthritis in some cases, although the reason for this is uncertain.
  
  
• Rheumatoid arthritis. People with rheumatoid arthritis experience inflammation of multiple joints. Certain symptoms of pseudogout may closely resemble rheumatoid arthritis, such as stiffness, fatigue and persistent restricted range of motion in joints. Furthermore, pseudogout may worsen the damage caused by rheumatoid arthritis if both are present in the same joint.
  
  
• Neuropathic joint disease. Diseases that can cause one or more joints to deteriorate and lose sensation (e.g., diabetes, tabes dorsalis and syringomyelia) may be accompanied by CPPD deposits. The affected joint is known as a Charcot joint. In these instances, the underlying cause of Charcot joint may be strengthened by the presence of a CPPD deposit.