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Stereotactic radiation for treating pituitary adenomas in cats

Wormhoudt TL, Boss MK, Lunn K, et al. Stereotactic radiation therapy for the treatment of functional pituitary adenomas associated with feline acromegaly. J Vet Intern Med. 2018 May 21. doi: 10.1111/jvim.15212.

Feline acromegaly is caused by a functional tumor (adenoma) of the pituitary gland leading to increased secretion of growth hormone (GH) and consequently insulin-like growth factor 1 (IGF-1) from the liver. Growth hormone can create effects that contribute to insulin resistance and eventually diabetes mellitus (DM). The clinical signs and laboratory results of acromegaly include polyphagia, polyuria, polydipsia, weight gain, insulin-resistant DM, enlargement of the head, paws, and internal organs, stertorous breathing, and central nervous system-associated signs. Male cats appear to be more commonly identified with this disease.

Stereotactic radiation therapy (SRT) is now an accepted form of treatment for many tumor types and locations in veterinary medicine. Conventional fractionated radiotherapy has been shown to be partially effective for management of pituitary tumors in cats. The investigators in this study wanted to evaluate the efficacy and safety of SRT as a treatment for acromegalic cats. Fifty-three client owned cats were evaluated and treated using SRT for pituitary tumors causing poorly controlled DM secondary to acromegaly. The median age of the cats at the time of treatment was 10 years of age, including 43 neutered male cats and 10 neutered females. The majority were domestic shorthair cats.

The results determined that the median survival time was 1072 days. The authors noted of the 41 cats where insulin dosage information was known, 95% (39/41) demonstrated a decrease in the required insulin dose, with 32% (13/41) achieving diabetic remission. Remission was noted to be permanent in 62% (8/13) and temporary in 38% (5/13) cats. The median duration of time to lowest insulin dose was 9.5 months. Seven of fifty cats (14%) developed hypothyroidism after SRT, in which the development of hypothyroidism was believed related to the therapy.

The authors conclude that SRT is a safe and effective treatment for pituitary tumors causing acromegaly in cats. Any acute radiation adverse effects were noted as minimal in this treated population, mild in severity, limited in duration and responsive to therapy. Late radiation effects were noted as including rare optic chiasm neuropathy, hypothyroidism and potential for late stage neurologic progression. SRT should be considered as a treatment for cats with acromegaly. (VLT)

See also:

Dunning MD, Lowrie CS, Bexfield NH, et al. Exogenous insulin treatment after hypofractionated radiotherapy in cats with diabetes mellitus and acromegaly. J Vet Intern Med. 2009 Mar-Apr;23(2):243-249.