Soft Tissue Mineralization in Captive 2-Toed Sloths

Abstract

Soft tissue mineralization was diagnosed in 19 captive 2-toed sloths ( Choloepus didactylus and Choloepus hoffmanni) ranging from 2 months to 41 years of age. Gross mineralization was evident at necropsy in 6 of 19 sloths and was prominent in the aorta and arteries. Histologically, 11 sloths had arterial mineralization, including mural osseous and chondroid metaplasia and smooth muscle hyperplasia consistent with arteriosclerosis. Visceral mineralization most commonly involved the gastric mucosa (17 sloths), kidneys (17 sloths), and lungs (8 sloths). Eleven sloths ranging in age from 5 to 41 years old had moderate to severe renal disease, which may be an important underlying cause of soft tissue mineralization in adult sloths. However, 5 sloths (juveniles and adults) had severe soft tissue mineralization with histologically normal kidneys or only mild interstitial inflammation or fibrosis, suggesting other causes of calcium and phosphorus imbalance. Degenerative cardiac disease was a common finding in 10 sloths with vascular mineralization and varied from mild to severe with fibrosis and acute noninflammatory myocardial necrosis. Although the prevalence of cardiac disease in adult sloths has not been documented, disease may be exacerbated by hypertension from degenerative arteriosclerosis as noted in this study group. Although renal disease likely contributed substantially to mineralization of tissues in most sloths in this study, nutritional causes of soft tissue mineralization—such as imbalances in dietary vitamin D or calcium and phosphorus—may be an important contributing factor.