Abstract

A 2.75-year-old male koala (Phascolarctos cinereus) presented with weight loss and polydipsia. Insulin-dependent diabetes mellitus (IDDM) was diagnosed based on serum glucose and insulin values and the homeostasis model assessment (HOMA). Repeated examinations, advanced imaging, hematology, serum biochemistry, and bone marrow cytology failed to detect a cause for IDDM but did reveal anemia with early myelodysplasia.

Treatment with three types of insulin failed to achieve predictable euglycemia, with very low doses occasionally causing hypoglycemia. To understand glucose response to insulin dosing, a continuous glucose monitor (CGM; Dexcom G6®) was placed in the paralumbar region. Interstitial glucose measured by the CGM correlated well with blood glucose values; however, the lifespan of each CGM decreased, and episodes of data dropout increased over time.

Approximately 9.5 months after diagnosis of IDDM, the koala developed pneumonia with rhinitis and otitis. Despite comprehensive treatment, including percutaneous endoscopic gastrostomy tube placement and voluntary nebulization, the koala’s health continued to decline. Humane euthanasia was performed.

Postmortem examination and histopathology confirmed the clinical diagnoses of IDDM, bacterial pneumonia with right middle lung lobe consolidation, and suppurative rhinitis and otitis media. Insulin and glucagon immunohistochemistry confirmed widespread atrophy of pancreatic islets, with severe loss of insulin-secreting beta cells and to a lesser extent alpha cells. Fasciitis and myositis were present at the sites of CGM placement associated with foreign material.

Diabetes mellitus in koalas is rare, with no reports of prolonged therapy. The CGM allowed for periods of improved glycemic control, but long-term stable euglycemia was never achieved.

Acknowledgments

We acknowledge SDZG’s histopathology laboratory for tissue processing and University of California, Davis Veterinary Medical Teaching Hospital’s histopathology laboratory for immunohistochemistry.