Practical relevance: Diabetes mellitus is the second-most common feline endocrinopathy, affecting an estimated 1/200 cats. While the underlying causes vary, around 15-25% of cats with diabetes mellitus develop the condition secondarily to progressive growth hormone (GH)-induced insulin resistance. This typically results in a form of diabetes that is challenging to manage, whereby the response to insulin is very variable or high doses are required to achieve even minimal diabetic control.
Clinical challenges: Although uncontrolled chronic excessive GH may result in phenotypic changes that raise suspicion for acromegaly, many cats with hypersomatotropism (HST) do not have these changes. In these situations, a clinician's index of suspicion may be increased by the presence of less dramatic changes such as marked polyphagia, stertor or uncontrolled diabetes mellitus. The current diagnostic test of choice is demonstration of a markedly increased serum insulin-like growth factor 1 (IGF1) concentration, but some affected cats will have only a marginal increase; additionally, chronic insulin administration in cats results in an increase in serum IGF1, making the diagnosis less clear cut and requiring additional confirmatory tests.
Evidence base: Over the past two decades, HST has increasingly been recognised as an underlying cause of diabetes mellitus in cats. This review, which focuses on diagnosis and treatment, utilises data from observational studies, clinical trials and case series, as well as drawing on the experience of the authors in managing this condition.
Keywords: IGF1; Insulin resistance; diabetes mellitus; growth hormone; pituitary.