Arthritis of diarthroidal or synovial joints of cetaceans is not well described in the literature. In humans and animals, arthritides are typically classified as degenerative, inflammatory, or reactive. Degenerative arthritis is a noninflammatory disorder of movable joints characterized by deterioration of articular cartilage and by formation of new bone at the joint surfaces and margins. Several factors have been implicated in the pathogenesis of degenerative arthritis, such as genetic predisposition, age, trauma, biochemical and metabolic abnormalities, and exercise-related factors. Inflammatory arthritis may be caused by infection, autoimmunity, or crystalline deposition. Inflammatory arthritides due to infection are caused by hematogenous spread of bacteria and viruses and through traumatic inoculation. Post-infectious arthritis can develop following meningococcal infections or enteric infections. Immune mediated inflammatory arthritides such as rheumatoid arthritis are chronic and systemic with unknown etiology. Cultures and gram stains of synovial tissue or joint effusions will typically identify only one third of infectious arthritis cases. Reactive arthritis is a synovitis with non-proliferating foreign antigens of microbial origin present in the joint tissue. Reactive arthritides are distinguished by the absence of live microbes in the joint tissue.

We found arthritis in synovial joints in 8 (4 male and 4 female) of 54 (14.8%) dolphins; 7 bottlenose dolphins (Tursiops truncates) and 1 Fraser's dolphin (Lagenodelphis hosei), examined at necropsy. The arthritis involved both the atlantooccipital and the humeroscapular joints; 6 out of 8 animals had involvement of the atlantooccipital joint, while 6 out of 7 had involvement of one or both humeroscapular joints. The lesions ranged from mild roughening to complete erosion of the articular cartilage with thickened synovium, and bony changes. Ankylosis of the atlantooccipital and humeroscapular joints was present in one animal. Other necropsy findings from these animals were variable including chronic meningitis (2 cases), sepsis, pneumonia, angiomatosis, amyloidosis, and heavy parasitism. The joints were cultured in 3 animals and one was positive for Vibrio alginolyticus. Blood and tissue cultures were positive for microorganisms in 4 of 5 animals tested.

The gross and histological findings in 4 of these 8 dolphins suggest degenerative or reactive type arthritis, while the other 4 are more suggestive of infection, although organisms were not demonstrated. The lesions do not appear to be a primary autoimmune type reaction. Based on body length and examination of the gonads, 2 of the animals were mature, while 6 were just approaching maturity. This suggests that the joint disorders in these animals are not a conventional degenerative arthritis which would be expected to affect older individuals. Arthritis is a debilitating disease which may be a significant mortality factor in younger animals. NIEHS Training Grant #T35 ES07294.