Arthralgia and crystal deposits in Crohn's disease

Ten patients with Crohn's disease and recurrent pain in the knee joints were subjected to arthroscopy. Biopsies obtained from the synovial membrane were examined under polarizing light microscopy. The arthroscopy revealed crystalline deposits in 7 patients and the microscopic examination of the synovial membrane demonstrated positively birefringent crystals in 4 patients. The crystals with positive birefringence had the rod or rhomboid shape typical of pyrophosphate crystals. As arthroscopy crystals in 7 patients and polarizing microscopy revealed crystals in one further patient, crystal deposits were thus found in 8 patients altogether. All patients had normal serum uric acid values. The crystal deposits were interpreted as pyrophosphate and their possible connection with the recurrent arthralgia in Crohn's disease is discussed.