Scanning Microscopy Volume 6 Number 3 Article 14 9-8-1992 Arthropathies Associated with Basic Calcium Phosphate Crystals Paul B. Halverson Medical College of Wisconsin Follow this and additional works at: https://digitalcommons.usu.edu/microscopy Part of the Biology Commons Recommended Citation Halverson, Paul B. (1992) "Arthropathies Associated with Basic Calcium Phosphate Crystals," Scanning Microscopy: Vol. 6 : No. 3 , Article 14. Available at: https://digitalcommons.usu.edu/microscopy/vol6/iss3/14 This Article is brought to you for free and open access by the Western Dairy Center at DigitalCommons@USU. It has been accepted for inclusion in Scanning Microscopy by an authorized administrator of DigitalCommons@USU. For more information, please contact [email protected]. Scanning Microscopy, Vol. 6, No. 3, 1992 (Pages 791-797) 0891-7035/92$5.00+ .00 Scanning Microscopy International, Chicago (AMF O'Hare), IL 60666 USA ARTHROPATHIES ASSOCIATED WITH BASIC CALCIUM PHOSPHATE CRYSTALS Paul B. Halverson Division of Rheumatology, Medical College of Wisconsin, 8700 W. Wisconsin Avenue, Milwaukee, WI 53226 Phone: 414-447-2597 (Received for publication July 23, 1992, and in revised form September 8, 1992) Abstract Introduction Basic calcium phosphate (BCP) crystals refer to a Basic calcium phosphate (BCP) crystals, usually re­ family of crystals including partially carbonate substi­ ferred to as "apatite" or hydroxyapatite, actually consist tuted hydroxyapatite, octacalcium phosphate, and trical­ of mixtures of partially carbonate-substituted hydroxy­ cium phosphate. These crystals have been found in and apatite, octacalcium phosphate, and tricalcium phosphate around joints and have been associated with several [39]. The latter two species may represent transition forms of arthritis and periarthritis . Identification of states leading to the final formation of hydroxyapatite. BCP crystals remains problematic because of the lack of These crystals have now been associated with a variety a simple, reliable analytic procedure. Methods currently of arthropathies yet their significance for the most part in use include alizarin red S staining, labelled diphos­ remains unclear. This review will discuss methods of phonate binding, scanning and transmission electron mi­ BCP crystal identification and the periarthropathies and croscopy with energy dispersive X-ray microanalysis, X­ arthropathies associated with BCP deposition (Table 1). ray diffraction, and atomic force microscopy. Periar­ thropathies associated with BCP crystals include calcific tendinitis and bursitis. Intra-articular BCP crystal deposition is common in osteoarthritis, often found to­ Table 1. Periarthropathies and arthropathies gether with calcium pyrophosphate dihydrate crystals. associated with basic calciwn phosphate (BCP) Uncommon conditions in which BCP crystals are found crystal deposition include destructive shoulder arthropathies, acute inflam­ matory attacks of arthritis, and erosive arthritis. Periarticular BCP arthropathies Secondary deposition of BCP crystals has been observed in chronic renal failure, in patients with "collagen Calcific periarthritis vascular" diseases, followingneurologic injury and after Calcific tendinitis local corticosteroid injection . Calcific bursitis Intra-articular BCP arthropathies Osteoarthritis with BCP crystals Mixed crystal deposition (BCP and CPPD) Milwaukee shoulder/knee syndrome (Idiopathic destructive arthritis, cuff tear arthropathy) Acute inflammatory attacks Key Words: Basic calcium phosphate, hydroxyapatite, Erosive polyarticular disease arthritis. Secondary BCP crystal arthropathy/periarthropathy Chronic renal failure Calcinosis in connective tissue diseases Post neurologic injury calcification Post corticosteroid injection Miscellaneous 791 Paul B. Halverson Methods of Detection of BCP Crystals and none has yet been shown to be clearly superior to the others. They are also unable to identify the site of BCP crystals are not birefringent. Thus, polarized origin of BCP crystals . Unfortunately, there is still no light microscopy, which is quite sensitive and specific simple, readily available method to detect BCP crystals for identifying the other two most common "pathologi­ comparable to polarized light microscopy for mono­ cal" crystals, monosodium urate monohydrate and cal­ sodium urate monohydrate and CPPD. cium pyrophosphate dihydrate (CPPD), is not useful for detecting BCP crystals. This is because individual BCP Periarthropathies associated with BCP crystals crystals, which are usually needle-shaped and less than 0.1 µm long, cannot be resolved by light microscopy Pathologic calcifications have been identified in a and are randomly oriented in the much larger aggregates wide variety of periarticular sites, most commonly in (2-19 µm) in which they are usually found. Occasional­ bursae and tendons, especially near the sites of tendon ly, light microscopy will reveal laminated bodies re­ insertions (entheses). For the most part, these appear to ferred to as "shiny coins" [37] but the usual appearance be isolated local dystrophic calcifications which are often of these crystals is nondescript. asymptomatic. Mechanisms causing dystrophic calcifica­ The calcium dye, Alizarin red S, has been utilized tion remain obscure . Local tissue damage, age related by some investigators to identify BCP crystals [43]. changes and perhaps other factors may predispose to cal­ Alizarin is highly sensitive but frequent false positive cification . In the rotator cuff, Uthoff and Sarkar [51] results suggest that it lacks sufficient specificity to found that "primary" calcifications occurred in areas of qualify for routine identification of BCP crystals without metaplastic fibrocartilage accompanied by matrix vesi­ some other type of confirmatory testing [2, 21]. cles and crystals being phagocytosed by macrophages We developed a semiquantitative binding assay for and giant cells. Others have not found chondrometa­ BCP crystals which utilires [14C] ethane-1-hydroxy-1,1- plasia and matrix vesicles but instead found calcifications diphosphonate (EHDP) [27]. This method is performed in psammoma bodies and necrotic cells [22]. Dystrophic on a synovial fluid pellet resuspended in phosphate buf­ calcification occurs with normal calcium and phosphorus fered saline and the results are expressed as µg/ml of concentrations in contrast to metastatic calcification hydroxyapatite standard. The limit of sensitivity is which occurs with disordered calcium or phosphorus approximately 2 µg/ml standard hydroxyapatite. metabolism. A few individuals have been described Both scanning and transmission electron microscopy with multiple areas of dystrophic calcification suggesting (SEM & TEM) with energy dispersive X-ray (EDX) mi­ the presence of a systemic disorder [37, 44]. Several croanalysis have been utilized to identify BCP crystals families in which multiple members have had articular in synovial fluid pellets [29]. TEM with electron dif­ and peri-articular calcifications provide evidence that a fraction is also effective [45]. For SEM the pellet is air heritable component may be present in some instances dried on a carbon planchet and sputter coated with car­ [7, 13, 23] . bon. Crystals may be released from tissue specimens by Many periarticular calcifications probably remain collagenase digestion [25]. Specimens to be examined asymptomatic and may only be discovered fortuitously by TEM must be fixed in glutaraldehyde and processed [5]. In some, though, dramatic inflammatory episodes by routine methods. Calcium:phosphorus molar ratios may occur with severe pain , swelling and erythema re­ vary from 1.3-1.7:1 [29]. This is consistent with sembling gout. Asymptomatic deposits are usually gritty Fourier transform infrared spectroscopy (FTIR) which and hard, whereas some symptomatic deposits may be has shown that BCP crystal deposits consist of mixtures aspirable and appear as a whitish paste. Acute calcific of hydroxyapatite, octacalcium phosphate, and rarely tendinitis refers to inflammation of the tendon sheath tricalcium phosphate crystals [39]. Amorphous calcium along with BCP crystal deposition. The most common phosphates may be detected by EHDP binding and site of tendon calcification is the supraspinatus of the possibly FTIR. shoulder. Other common sites include the wrist, hip and X-ray diffraction definitively identifies BCP crystals knee but no site should be considered immune. This en­ although the quantity of crystals necessary for analysis tity differs from non-calcific tendinitis in that it is less exceeds that required for the other techniques . likely to be related to trauma and inflammation tends to Atomic force microscopy has been recently applied be more severe. Calcific bursitis refers to calcification to the identification of synovial fluid microcrystals [4]. and inflammation in one of the many cell lined bursal This technique is capable of achieving subnanometer sacs which facilitate movement of tissues usually over resolution of crystal surface topology and measurement bony prominences. One type, subacromial calcific bur­ of lattice unit cell dimensions. sitis, is thought to occur when preformed, usually These techniques have not been rigorously compared asymptomatic deposits of BCP crystals, rupture into the 792 Arthropathies Associated with Basic Calcium Phosphate Crystals bursa. affected by osteoarthritis [17, 48). Synovial fluid dem­ Mechanisms of calcification remain obscure. Local onstrated hydroxyapatite crystals and elevated