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Intracellular and extracellular CPPD crystals are a regular feature in synovial fluid from uninflamed joints of patients with CPPD related arthropathy
  1. A Martínez Sanchis,
  2. E Pascual
  1. Sección de Reumatología, Hospital General Universitario de Alicante, C/Pintor Baeza s/n, 03010 Alicante, Spain;
  1. Correspondence to:
    Dr Agustin Martínez Sanchis
    Calle Pintor Baeza, s/n Alicante 03010, Spain;


Objectives: To determine whether calcium pyrophosphate dihydrate (CPPD) crystals can be found in the synovial fluid of non-inflamed joints in patients with CPPD related arthropathy; if so, to determine whether they interact with cells and produce subclinical inflammation in this setting.

Methods: 74 synovial fluid samples were obtained from non-inflamed knees of 74 patients with CPPD related arthropathy. Identification of CPPD crystals and synovial fluid cell counts were done manually in undiluted samples using a haematocytometric chamber. A supravital stain (Testsimplets, Boehringer Mannheim) was used to carry out differential counts and to assess the presence of intracellular crystals.

Results: All 74 samples contained CPPD crystals. The mean cell count was 301.4 cells/μl (95% confidence interval (CI), 216.6 to 386.4; range 22 to 2302.5). Mononuclear cells accounted for 83.2% (95% CI, 80.4% to 86.1%; range 43% to 99%), the rest being polymorphonuclear (PMN) cells (16.8% (95% CI, 13.9% to 19.6%; range 1% to 57%)). All the samples contained intracellular CPPD crystals, which were found in 24.0% of all the cells (95% CI, 20.1% to 27.9%; range 1% to 78%). Most of the intracellular crystals were inside mononuclear cells (22.2% of all the cells (95% CI, CI 18.5% to 25.9%)), although some PMN also contained them (1.8% of all the cells (95% CI, 1.1% to 2.4%)).

Conclusions: CPPD crystals are normally found in synovial fluid of non-inflamed joints of patients with CPPD related arthropathy, and they interact with cells. The raised cell counts and percentage of PMN suggest mild subclinical inflammation in these joints.

  • CPPD, calcium pyrophosphate dihydrate
  • MSU, monosodium urate
  • NSAID, non-steroidal anti-inflammatory drugs
  • PMN, polymorphonuclear neutrophil white blood cells
  • calcium pyrophosphate dihydrate deposition
  • pseudogout
  • chondrocalcinosis
  • synovial fluid

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