Background Arthropathy induced by calcium pyrophosphate dihydrate [Ca₂P₂O₇.2H₂O] (CPPD) crystals (chondrocalcinosis, pseudogout, pyrophosphate arthropathy) and arthropathy induced by hydroxyapatite [Ca₅(PO₄)₃(OH)] (HA) crystals (apatite rheumatism, Milwaukee syndrome) are regarded as distinct clinical entities [1–3].

This distinction is justifiable clinically by the different localization and symptoms of CPPD and HA crystal depositions, and is supported by the observation of the crystals in conventional hematoxylin-eosin (H-E) stained histological sections. In H-E stained sections viewed under polarized light in case of chondrocalcinosis the CPPD crystals are detectable, while the more soluble HA crystals in case of apatite rheumatism are not.

The probability of identifying crystals is much higher in unstained sections viewed under polarized light, than in H-E stained ones [4,5].

Objectives The aim of this study was to detect and compare the prevalence of CPPD and HA crystals in H-E stained and unstained sections in clinically diagnosed chondrocalcinosis and apatite rheumatism.

Methods Eighteen (18) tissue samples of 10 patients with clinically diagnosed chondrocalcinosis, and ten (10) tissue samples of 3 patients with clinically diagnosed apatite rheumatism were studied in serially cut histologic sections of formalin fixed and paraffin embedded tissue blocks. The sections stained with H-E and unstained sections were viewed under polarized light with an Olympus BX51 polarization microscope.

Results The H-E stained sections were examined under polarized light; CPPD crystals were detected in all 10 patients with clinically diagnosed chondrocalcinosis, and HA crystals were detected in 1 of 3 patients with clinically diagnosed apatite rheumatism.

In unstained sections viewed under polarized light CPPD and HA crystals were present in all 13 patients with different prevalence (dominance).

In unstained sections CPPD dominated the crystal deposits in 6 of 13 patients (with sporadic presence of HA). The presence of HA crystals was absolutely dominant in crystal deposits in 4 of 13 patients (with sporadic presence of CPPD). The presence of CPPD and HA crystals was equal in 3 of 13 patients.

Conclusions There is a difference in the shape, size, and intensity of birefringence of CPPD and HA crystals, furthermore in their solubility in conventional fixatives (formalin) and other aqueous solutions (e.g. dyes).

The presence of CPPD and the absence of HA crystals in H-E stained histologic sections supports the distinction between chondrocalcinosis and apatite rheumatism.

In unstained histologic sections variable amounts of CPPD and HA crystals were demonstrated in clinically diagnosed cases. Based on these findings the chondrocalcinosis and apatite rheumatism may represent different clinical manifestations and symptoms of the same metabolic disorder.

1. Reginato AJ, Reginato AM: In Kelly's Textbook of Rheumatology, 2001, ch. 90, page 1377–1390

2. Gardner DL, McClure J: In Pathological basis of the connective tissue diseases, 1992, ch. 10, pages 393–402 and 405–407

3. McCarty DJ, Lehr RJ, Halverson PB: Arthritis and Rheumatism 1983; 26: 1220–1224

4. Bély M, Apáthy Ά: DOI: 10.1136/annrheumdis-2014-eular.3120

5. Bély M, Apáthy Ά: DOI: 10.1136/annrheumdis-2014-eular.3127

Disclosure of Interest None declared