Tophaceous pseudogout in a 12-year-old dog, with a review of applicable laboratory tests.

Pseudogout, also known as calcium pyrophosphate dihydrate (CPPD) deposition disease or chondrocalcinosis, is caused by crystalline deposits of CPPD within the extracellular matrix of articular hyaline cartilage and fibrocartilage, and within articular and periarticular connective tissue. Using a variety of laboratory techniques, we diagnosed pseudogout in the right hindlimb digit V of a 12-y-old Standard Poodle. Histologically, the joint, bone, tendon, and dermis were expanded and effaced by masses of mineralized, rhomboid crystals surrounded by macrophages, multinucleate giant cells, fibrous connective tissue, and chondroid and osseous matrix. Rhomboid crystals exhibiting weak-positive birefringence were identified under polarized light using a first-order red compensator filter. Scanning electron microscopy with energy-dispersive x-ray analysis (SEM-EDXA) revealed that the rhomboid crystals were composed of calcium, phosphorus, and oxygen. Fourier-transform infrared (FTIR) microspectroscopy confirmed the presence of calcium pyrophosphate. In dogs, tophaceous pseudogout, which was the variant of pseudogout in our case, occurs as a single, tumor-like periarticular mass that can be invasive and mimic neoplasia. Having ancillary confirmatory testing (SEM-EDXA and FTIR), particularly in unusual histologic scenarios, such as tophaceous pseudogout in dogs, is desirable for confirming the correct diagnosis, even though it is available only at certain reference centers. The pathogenesis of pseudogout is unknown.

Tophaceous pseudogout of the femorotibial joint in a painted turtle (Chrysemys picta).

A 5-year-old painted turtle (Chrysemys picta) presented with a 1cm nodular enlargement of the right femorotibial joint. The right leg was amputated, because the nodule continued to grow and motor problems appeared. The cut surface of the nodule was yellowish white, and had a colloidal to chalky gross appearance. Microscopically, a multinodular foreign-body granuloma was observed around the joint capsule. Morphological and histochemical examination showed that the foreign body consisted of calcium pyrophosphate. Histological findings revealed that the articular cartilage was mainly involved in the pathological onset of the disease, and was therefore diagnosed as tophaceous pseudogout. This disease is generic in elderly people, but is rare in animals. Also, there are only three reports in reptiles.

Articular gout and suspected pseudogout in a Basilisk lizard (Basilicus plumifrons).

A 9-yr-old male Basilisk lizard (Basilicus plumifrons) with a history of painful and limited mobility for approximately 4 mo, which had seemed to be more pronounced in the front limbs, was presented for necropsy. The animal had exhibited moderate weight loss and anorexia before euthanasia. Postmortem examination revealed yellow-to-white, soft-to-semifirm nodules within the periarticular fascia and musculature of the left and right shoulder joints, hip joints, and stifle joints. Several other joints, including the left and right tarsi, left and right elbow joints, and the left carpus had calcified, white material present on the articular surfaces. Histopathologic evaluation of representative sections of all organs and the joints confirmed tophaceous articular gout and articular pseudogout. The differentiation between articular gout and pseudogout was based on histologic appearance, histochemical staining for calcium, and birefringence under polarized light.

Possible pseudogout in two dogs.

Pseudogout, the acute form of calcium pyrophosphate deposition disease, is a common condition in elderly human beings and is characterised by the sudden onset of intense joint pain and synovitis. It is rarely identified in animals but was diagnosed in two dogs that presented with acute lameness and pyrexia. Cytology of the synovial fluid showed a mildly elevated cell count with both non-degenerate neutrophils and mononuclear cells present. Many of the mononuclear cells and occasional neutrophils contained square or rhomboid-shaped crystals that were variable in shape and size and weakly birefringent on examination under polarised light. Clinical signs resolved following treatment with prednisolone.

Skeletal survey of Cayo Santiago rhesus macaques: osteoarthritis and articular plate excrescences.

OBJECTIVES: This study was performed to complement studies on spondyloarthropathy in rhesus macaques by quantifying and characterizing another major form of arthritis and contrasting it with osteoarthritis. METHODS: Skeletons of 269 macaques of known age and troop affiliation from the free-ranging Cayo Santiago colony (Caribbean Primate Research Center) were macroscopically surveyed for the presence of articular changes of osteoarthritis, articular plate excrescences, and calcifications that project back over the joint surface in all diarthrodial joints. Statistical tests were used to establish the independence of pathological conditions, age, gender, troop membership, and specific joint involvement. RESULTS: Subchondral articular surface excrescences or calcific plate-like articular surface overgrowth were noted in 17% and osteoarthritis in 18% of Cayo Santiago macaques. Distribution of joint involvement and sex ratio (1:1) of the former condition were independent of either troop membership or the distribution of osteoarthritis. CONCLUSION: Three major forms of arthritis are common in rhesus macaques: osteoarthritis, spondyloarthropathy, and a category that might be referred to as apical plate excrescences (APE). The latter is very different from spondyloarthropathy, rheumatoid arthritis, osteoarthritis, gout, and infectious arthritis. It is quite similar to what in the past has been referred to as the radiographic form of calcium pyrophosphate deposition disease (CPPD) in humans. A new name has not been offered for the identification/categorization of this phenomenon in dry bone. Its occurrence in rhesus macaques appears to present a natural model for characterization of genetic, immunologic, and environmental aspects of this phenomenon. The acronym APE is offered for consideration in naming this category of arthritis in skeletal material.

Crystals in equine articular cartilage.

Crystal deposits have been observed in equine articular cartilage and identified by scanning electron microscopy and X-ray diffraction as octacalcium phosphate and calcium pyrophosphate dihydrate. Of 89 equine fetlock joints examined 10 contained evidence of calcification visible by eye. It is suggested that the deposition of crystals may be a mediator of arthritis in horses and may also cause damage directly.

Calcium crystal-associated arthropathy (pseudogout) in a dog.

Calcium pyrophosphate dihydrate (Ca2P2O7.2H2O) crystal-associated arthropathy (pseudogout) was diagnosed in a dog. Clinical signs included non-weightbearing lameness, signs of pain on joint manipulation, and high rectal temperature. Arthrocentesis of carpal joints revealed extra- and intracellular crystals containing calcium. The suspected cause was polyarthritis secondary to chronic Ehrlichia infection. Results of joint tap performed after resolution of the clinical signs were negative for calcium pyrophosphate dihydrate crystals.