Abstract
<title>Abstract</title> <p>Background Diabetes mellitus (DM) in dogs is most commonly associated with insulin deficiency; however, insulin resistance-associated DM may occur secondary to hormonal disorders and can be reversible when the underlying cause is eliminated. Ovarian tumors, including granulosa cell tumors (GCTs), may be hormonally active, but their association with clinically relevant insulin-resistant DM has rarely been described. Case presentation A 14-year-old intact female Yorkshire Terrier weighing 6.2 kg was evaluated for polyuria, polydipsia, and hyperglycemia. Initial diagnostics revealed marked hyperglycemia (443 mg/dL), glucosuria, and increased fructosamine concentration without clinically significant ketoacidosis. Abdominal imaging identified a small, homogeneous right ovary and a large cystic mass arising from the left ovary. Despite insulin therapy (up to 4 U/dog), the patient’s glycemic control remained poor, with glucose concentrations ranging from approximately 350 mg/dL at nadir to the upper detection limit of 500 mg/dL. Hormonal analysis revealed increased progesterone and insulin-like growth factor-1 concentrations despite the absence of luteal structures on imaging. Ovariohysterectomy (OHE) was performed, and histopathology confirmed a GCT with marked atrophy of normal ovarian parenchyma and absence of a corpus luteum, which is inconsistent with physiological diestrus. The patient’s blood glucose concentrations rapidly improved postoperatively, allowing discontinuation of insulin therapy within 24 hours. Glucosuria resolved within two days, and euglycemia was maintained without further insulin administration, with normalization of fructosamine concentrations within one to two weeks. Conclusions This case demonstrates that complete diabetic remission is achievable after OHE in dogs with a functional ovarian GCT. Functional ovarian neoplasia should be considered alongside diestrus and pyometra as a cause of progesterone-mediated insulin resistance in intact female dogs, in which timely surgical excision may achieve rapid diabetic remission.</p>