Exogenous Insulin Treatment after Hypofractionated Radiotherapy in Cats with Diabetes Mellitus and Acromegaly

Abstract

Background: The optimal treatment for feline acromegaly has yet to be established. Surgical and medical therapies are minimally effective although radiotherapy might have greater efficacy. The purpose of this study was to review the response and outcome of cats with acromegaly and insulin-resistant diabetes mellitus (DM) to radiotherapy.Hypotheses: That radiotherapy improves glycemic control in cats with acromegaly and that improved glycemic control is due to remission of clinical acromegaly; demonstrated by a fall in serum insulin-like growth factor-1 (IGF-1) concentrations.Animals: Fourteen cats with naturally occurring acromegaly. Methods: Retrospective case review; records of all cats treated for acromegaly with radiotherapy were reviewed from 1997 to 2008. Cats were selected on the basis of compatible clinical signs, laboratory features, and diagnostic imaging findings. Fourteen cats received radiotherapy, delivered in 10 fractions, 3 times a week to a total dose of 3,700 cGy.Results: Thirteen of 14 cats had improved diabetic control after radiotherapy. These improvements were sustained for up to 60 months. DM progressed in 2 cats and 1 did not respond. Seven cats responded before the final treatment. Ten cats were euthanized, 1 as a consequence of radiotherapy. In 8 cats in which IGF-1 was measured after treatment, changes in its concentration did not reflect the clinical improvement in glycemic control.Conclusions and Clinical Importance: Radiotherapy represents an effective treatment for cats with insulin-resistant DM resulting from acromegaly. IGF-1 concentration after treatment does not provide a suitable method by which remission from either acromegaly or insulin-resistant DM may be assessed.

Linear‐Accelerator‐Based Modified Radiosurgical Treatment of Pituitary Tumors in Cats: 11 Cases (1997–2008)

“…Clinical signs in cats with pituitary tumors usually are a consequence of either hypercortisolemia secondary to increased ACTH secretion, insulin-resistant diabetes mellitus (DM), and other changes that constitute the syndrome of acromegaly secondary to increased growth hormone (GH) secretion, or the space-occupying nature of a mass. [1][2][3][4][5][6][7] Treatment options for cats with pituitary tumors include surgical interventions such as hyphophysectomy or adrenalectomy, medical management of the endocrine consequences, or radiation therapy (RT). [1][2][3][4][5][6][7][8][9][10] Adrenalectomy is considered the treatment of choice for cats with pituitary-dependent hyperadrenocorticism (PDH) 9 ; hypophysectomy has seen limited application in cats with few reported animals having had the procedure performed.…”

Serum N‐Terminal Type III Procollagen Propeptide: An Indicator of Growth Hormone Excess and Response to Treatment in Feline Hypersomatotropism

“…As in previous studies, no significant difference was found in IGF‐1 concentration pre‐ and post‐RT in HSDM cats . Ideally, more cats would have been recruited into this group.…”

“…Indeed, even in cases which see diabetes resolved after RT, ongoing soft tissue changes have been observed . Alternatively, RT may be associated with a late onset of treatment effect . Cats therefore may not have yet fully responded to RT, and GH concentration may still have been high, leading to ongoing body‐wide increased soft tissue turnover.…”

“…However, IGF‐1 production also is influenced by other factors, including availability of portal venous insulin, which in turn depends on remaining beta‐cell function or exogenous insulin provision. Finally, serum IGF‐1 concentration has been shown to be a poor marker of treatment success after radiotherapy (RT) in cats with diabetes and HS …”

Feline Hypersomatotropism, an Important Cause for the Failure of Insulin Therapy

“…Increasing weight despite poor blood glucose control should be one of the factors indicating an underlying IR inducing endocrinopathy. A high percentage of diabetic hypersomathotropic cats displayed poorly controlled blood glucose and required highly dangerous doses of insulin (Dunning et al, 2009;Feldman and Nelson, 2000;Niessen, 2010;Slingerland et al, 2008). Severe episodes of hypoglycemia are at risk, as GH has a pulsatile episodic secretion, leaving luctuating gaps in the IR, when insulin could have a normal hypoglycemic effect.…”