Feline acromegaly: The keys to diagnosis - Veterinary Medicine
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Feline acromegaly: The keys to diagnosis
Caused by excessive growth hormone secretion, this likely underdiagnosed endocrinopathy may be lurking in your feline patients—especially older, poorly controlled diabetic males. Here's a look at which diagnostic tests can help you detect it.


VETERINARY MEDICINE


Diagnostic imaging

Radiographic findings associated with feline acromegaly are related to the hypertrophic or anabolic effects of excessive growth hormone. Hyperostosis of the calvarium, spondylosis of the spine, and protrusion of the mandible are common findings. Periosteal reaction, osteophyte production, soft tissue swelling, and collapse of joint spaces are signs associated with the degenerative arthropathy linked to feline acromegaly. Thoracic radiography may reveal cardiomegaly and congestive heart failure. Nonspecific signs such as abdominal organomegaly (hepatic, renal, adrenal) may be revealed by abdominal radiography and ultrasonography.

Advanced imaging is needed to document the presence of a pituitary adenoma. Computed tomography and magnetic resonance imaging (MRI) are both useful for identifying pituitary masses.10,11 However, MRI is thought to be the more sensitive imaging modality.

The presence of a pituitary tumor alone is not diagnostic for feline acromegaly since other functional tumors of the pituitary gland, such as ACTH-producing tumors in patients with Cushing's disease, may also result in insulin-resistant diabetes. Conversely, the absence of a pituitary mass does not rule out acromegaly since a case has been reported in which a patient had negative MRI results but a pituitary mass was identified at necropsy and histopathology results confirmed feline acromegaly.6

Histologic examination

Histologic examination of the pituitary tumor is necessary for a definitive diagnosis, which makes antemortem diagnosis challenging. However, with advances in surgical procedures, such as transsphenoidal hypophysectomy, surgical excisional biopsy is possible. The main histologic change associated with acromegaly is proliferation of somatotrophs.1

Adrenocortical testing

As stated earlier, a common presenting complaint for patients with acromegaly is insulin resistance with weight gain. Although rare, hyperadrenocorticism can be mistaken for feline acromegaly since both of these diseases can be associated with insulin-resistant diabetes mellitus (and associated clinical signs), a pituitary mass, and bilateral adrenomegaly. As such, hyperadrenocorticism is an important differential diagnosis to keep in mind should diagnostic testing for feline acromegaly produce vague or unequivocal results.

CONCLUSION

Feline acromegaly is likely an underdiagnosed disease in older male cats, especially in ones with insulin-resistant diabetes. A recent study in the United Kingdom measured IGF-1 concentrations in variably controlled diabetic cats. Of the 184 cases, 59 (32%) had markedly increased IGF-1 concentrations. Eighteen of these 59 cats underwent pituitary imaging, confirming a diagnosis of acromegaly in 17/18 (94%).6 This study illustrates the importance of ensuring that we remain aware of feline acromegaly so that we may more consistently diagnose and treat these patients.

For information regarding treatment options in cats with acromegaly, see the article "Feline acromegaly: Treatment options".

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


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Source: VETERINARY MEDICINE,
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