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6 Feline Acromegaly 47

Radiation had improved insulin responses. The average insulin dos
VetBooks.ir Radiation therapy is another option for the treatment of age reduction was approximately 75%. Six of the cats went
into complete diabetic remission and at the time the article
feline acromegaly, especially if the tumor is inoperable,
the patient is not a suitable candidate for anesthesia, or was written, 3/6 remained in remission. The median sur
vival time of cats in this study was 28 months.
surgical treatment is not available in the area. In human The most promising results with radiation may involve
medicine, radiation therapy is regarded as a second‐line the use of stereotactic radiation therapy (SRT). Fifty‐
treatment as beneficial effects may take years to develop three client‐owned cats were referred to Colorado State
and the patient typically experiences undesired late‐term University for
CNS radiation effects. SRT to treat pituitary tumors causing poorly controlled
The majority of studies that have been performed in vet
erinary medicine focus on radiation treatment of pituitary diabetes mellitus (DM) secondary to acromegaly.
Diagnosis of acromegaly was based on history, physical
masses regardless of functional status. There is no standard examination, laboratory results, and cross‐sectional
treatment protocol for pituitary masses in veterinary medi imaging of the pituitary. Signalment, radiation protocol,
cine and varying methods have been used, including both insulin requirements over time, adverse effects, and sur
single and multiple dose fractions administering total dos vival were recorded. Median survival time was 1072 days.
ages ranging from 1500 to 4000 cGY. The majority of the Of the 41 cats for which insulin dosage information was
cats included in these studies had insulin‐resistant diabetes available, 95% (39/41) experienced a decrease in required
(suspected acromegaly or Cushing disease) and/or neuro insulin dose, with 32% (13/41) achieving diabetic remis
logic signs. Radiation therapy was shown to be successful sion. Remission was permanent in 62% (8/13) and tem
in improving insulin resistance and neurologic signs. porary in 38% (5/13) cats. Median duration to lowest
Neurologic improvement was generally seen within weeks insulin dose was 9.5 months. Of the treated cats, 14%
to months and an improved insulin response was seen developed hypothyroidism and required supplementa
within the first month, but most patients still required insu tion after SRT. Cats treated with SRT have improved sur
lin therapy. In cases where repeat imaging was available, a vival time and control of their DM when compared to
decrease in tumor size was also noted. previously reported patients treated with non‐SRT.
Disadvantages of radiation therapy are the early and
delayed effects of radiation, repeated anesthesia, and
expense. Early effects from radiation therapy include
hair loss, skin pigmentation, and otitis externa. Reported Conclusion
late‐term side‐effects include brain necrosis, tumor
regrowth, and visual and hearing impairment. Feline acromegaly is likely an underdiagnosed disease in
In one study, 12 cats with pituitary tumors were treated older male cats, especially in patients with insulin‐resistant
with a coarse fractionated radiation protocol delivering a diabetes. There is no single diagnostic test for acromegaly.
total dose of 37 Gy in five once‐weekly doses. Eight of these The diagnostician should use history, clinical signs, labora
cats had insulin‐resistant diabetes mellitus secondary to tory tests (GH and IGF‐1), and advanced imaging to arrive
acromegaly. Of these eight cats, five no longer required at a diagnosis. There are several treatments options, but
insulin therapy, two became stable diabetics, and one clinical studies on long‐term safety and efficacy are limited
required less insulin. In addition, 3/4 cats had improved and often lack controls. Until more work is done evaluat
neurologic signs. The mean survival time of cats in this ing medical treatments such as somatostatin analogs and
study was approximately 18 months. In another study, 14 growth hormone antagonists, most patients are best
cats with confirmed acromegaly and insulin‐resistant dia treated with either surgery or radiation therapy to control
betes were treated with a total dose of 3700 cGy divided GH levels, improve glycemic control, and improve or pre
into 10 fractions (three per week). Thirteen of the 14 cats vent the development of neurologic signs.