Surgically removing the pituitary tumor (adenectomy) is the treatment of choice in people with acromegaly. The procedure can
be performed in cats and dogs but typically results in the complete removal of the pituitary gland (hypophysectomy). Complications
associated with the surgery include hemorrhage and incision dehiscence. After surgery, patients require treatment with cortisone,
L-thyroxine, with or without desmopressin, to compensate for the loss of pituitary function. Because of this, only patients
that are easily medicated should be considered for this procedure.
Few case reports exist for the treatment of feline acromegaly with transsphenoidal hypophysectomy. In one case, a patient
was receiving 25 U of insulin detemir (Levemir—Novo Nordisk) four times a day before surgery, and three weeks after surgery,
the patient no longer required insulin therapy.8 Up to one year later, the patient's insulin-like growth factor-1 (IGF-1) and growth hormone concentrations remained normal.
In a case we treated at VCA West Los Angeles Animal Hospital, a 13-year-old castrated male domestic shorthaired cat with acromegaly
underwent transsphenoidal hypophysectomy. The patient had a history of insulin-resistant diabetes mellitus and was receiving
15 U of insulin glargine every 12 hours. The patient's diabetes mellitus resolved two weeks after the surgery and remained
in remission for eight months, at which time the cat was euthanized for an unrelated issue.
Availability of this procedure is limited in the United States, and as of this writing, the procedure is only available at
the VCA West Los Angeles Animal Hospital, although other institutions may soon be able to offer this option.
Radiation therapy is another option for the treatment of feline acromegaly, especially if the tumor is inoperable or surgical
treatment is not available in the area. In human medicine, radiation therapy is regarded as a second-line treatment since
beneficial effects may take years to develop and patients typically experience undesired late-term central nervous system
Most studies that have been performed in veterinary medicine focus on radiation treatment of pituitary masses regardless of
functional status. There is no standard treatment protocol for pituitary masses, and varying methods have been used, including
both single- and multiple-dose fractions, administering total doses from 1,500 to 4,500 cGY.9-14 Most of the cats included in these studies had insulin-resistant diabetes (suspected acromegaly or Cushing's disease) or
Radiation therapy has been shown in these studies to be successful in improving both insulin resistance and neurologic signs.
Neurologic improvement was generally seen within weeks to months. Improved insulin response was seen within the first month;
however, most patients still required insulin therapy. In cases in which repeat imaging was available, a decrease in tumor
size was also noted.
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.12,14 Reported late-term side effects include brain necrosis, tumor regrowth, loss of vision, and hearing impairment.11,12
In one study, 12 cats with pituitary tumors were treated with a coarse fractionated radiation protocol, delivering a total
dose of 37 Gy in five once-weekly doses.9 Eight of these cats had insulin-resistant diabetes mellitus secondary to acromegaly. After radiation therapy, five of the
eight cats no longer required insulin therapy, two became stable diabetics, and one required less insulin. In addition, three
of four cats had improved neurologic signs. The mean survival time of cats in this study was about 18 months.
In another study, 14 cats with confirmed acromegaly and insulin-resistant diabetes mellitus were treated with a total dose
of 3,700 cGy divided into 10 fractions (three a week).10 Thirteen of the 14 cats had improved insulin responses, with an average insulin dosage reduction of about 75%. Six of the
cats went into complete diabetic remission, and three of the six remained in remission at the time of this writing. The median
survival time of cats in this study was 28 months.
Many options exist for treating feline acromegaly. However, clinical studies on their long-term safety and efficacy are limited
and often lack controls. Until more work is done evaluating medical treatments such as somatostatin analogues and growth hormone
antagonists, most patients are best treated with radiation therapy or surgery to control growth hormone concentrations and
neurologic signs, or with increased insulin doses to improve glycemic control.
When making your recommendation regarding treatment, be sure to consider the patient's clinical status (state of diabetes
control, any coexisting diseases, whether or not it is a candidate for anesthesia), the availability of treatments in your
area, and the advantages and disadvantages of each treatment modality.
Justin Wakayama, DVM Department of Veterinary Clinical Sciences College of Veterinary Medicine University of Minnesota St.
Paul, MN 55108
David S. Bruyette, DVM, DACVIM VCA West Los Angeles Animal Hospital 1900 S. Sepulveda Blvd. West Los Angeles, CA 90025
Veterinary Diagnostic Investigation and Consultation 26205 Fairside Road Malibu, CA 90256