Abstract

A 10-year-old intact female Western lowland gorilla (Gorilla gorilla gorilla) housed at the Columbus Zoo and Aquarium was evaluated for episodic bouts of lethargy, trembling, and stupor occurring January to February 2001. On visual exam, the animal appeared alert, though slightly lethargic, with mild shaking of the hands. Clinical signs seemed self-limiting, typically more prominent in the morning, and steady improvement occurred throughout the day. Review of the animal’s medical history revealed that similar clinical signs had been observed during a first pregnancy, which began in August 1998. Serum chemistry panels on two separate occasions during this pregnancy documented hypoglycemia (Table 1). One of these hypoglycemic occasions correlated with petit mal seizures and unconsciousness.

Table 1. Serum concentrations of glucose, insulin, proinsulin, and C-peptide in three Western lowland gorillas

^aReportedly healthy intact female gorilla of similar age
^bReportedly healthy intact male gorilla of similar age
^cAffected animal

With this history and current clinical signs, episodic hypoglycemia was suspected. Differential diagnoses for this presentation included pancreatic islet cell tumor (insulinoma), mesenchymal tumor, autoimmune hypoglycemia, and reactive hypoglycemia. Banked sera from this animal and two other similarly aged, reportedly healthy, Western lowland gorillas were submitted for measurement of glucose, insulin, proinsulin, and C-peptide levels (Table 1). Based on these results, a diagnosis of insulinoma was highly suspected.

In April 2001, localization of the suspected tumor was attempted. The gorilla was immobilized with tiletamine/zolazepam (Telazol®, Fort Dodge Animal Health, Fort Dodge, IA, USA, 2.3 mg/kg IM) for transport to the Ohio State University School of Veterinary Medicine. Anesthesia was maintained by isoflurane (IsoFlo®, Abbott Laboratories, North Chicago, IL, USA) to perform a celiac angiogram and contrast-enhanced computed tomography (CT). The angiogram demonstrated a small, abnormal contrast “blush” in the region of the head of the pancreas. CT with arterial phase contrast also revealed a contrast-enhanced mass in the region of the head of the pancreas, measuring approximately 4 cm.

Exploratory laparotomy was performed in June 2001 using the previously described anesthetic protocol. Utilizing intraoperative ultrasound, a hypoechoic region was identified within the tail of the pancreas. Partial pancreatectomy was performed, and the excised portion was submitted for histopathology. This evaluation demonstrated no discrete neoplasm. However, the pancreatic parenchyma had a multinodular to multilobular pattern with increased numbers and hyperplasia of islets. A final diagnosis of nesidioblastosis was made based on histopathologic findings. This is the first reported case of nesidioblastosis in a nonhuman primate.