Feline Acromegaly: An Underdiagnosed Endocrinopathy?

CT and MRI evaluation of skull bones and soft tissues in six cats with presumed acromegaly versus 12 unaffected cats

Feline acromegaly is predominantly caused by an adenoma of the pituitary gland, resulting in excessive growth hormone and insulin-like growth factor (IGF-1) secretion. In advanced cases, cats will display prominent facial features and upper airway congestion secondary to bony and soft tissue proliferation. The purpose of this study was to describe CT and MRI characteristics of soft tissues and skull bones in six cats with presumed acromegaly and to compare findings with those observed in 12 unaffected cats. In the five acromegalic cats with CT or MRI evidence of a pituitary tumor, frontal bone thickness was greater than age-matched controls with and without a history of upper airway disease. These five cats also had evidence of soft tissue accumulation in the nasal cavity, sinuses, and pharynx. One cat with insulin-resistant diabetes mellitus, elevated IGF-1, and a normal pituitary size did not have evidence of frontal bone thickening or upper airway congestion.

Successful treatment of acromegaly in a diabetic cat with transsphenoidal hypophysectomy

PATIENT AND SURGICAL TREATMENT: An 11-year-old, castrated male cat was referred for insulin-resistant diabetes mellitus. It had a ravenous appetite, increased body weight, polyuria/polydipsia and a dull hair coat. The cat was receiving 25 IU insulin four times daily but blood glucose concentrations remained elevated. Plasma concentrations of growth hormone (GH) (51 microg/l, reference range 0.8-7.2 microg/l) and insulin-like growth factor 1 (IGF-1) (3871 microg/l, reference range 39-590 microg/l) were highly elevated, whereas those of alpha-melanocyte-stimulating hormone, adrenocorticotropic hormone and cortisol were normal. Computed tomography revealed a thick palatum molle and an enlarged pituitary gland, indicating a pituitary neoplasm. Microsurgical transsphenoidal hypophysectomy was performed and microscopic examination of the surgical specimen revealed an acidophilic, infiltrative pituitary adenoma that showed positive immunostaining for GH.

OUTCOME

The clinical signs resolved and 3 weeks after surgery the cat no longer required insulin administration. One year after hypophysectomy the plasma concentrations of GH and IGF-1 were 2.4 microg/l and 113 microg/l, respectively.

PRACTICAL RELEVANCE

This is the first report detailing transsphenoidal hypophysectomy as a feasible and effective treatment for feline acromegaly due to a pituitary somatotroph adenoma. Moreover, in this patient, concurrent insulin-resistant diabetes mellitus resolved completely. The surgery is discussed in the context of human and other feline therapies for acromegaly.

Feline acromegaly: an essential differential diagnosis for the difficult diabetic

PRACTICAL RELEVANCE

Clinicians who deal with diabetic cats can have mixed experiences. Some patients are 'textbook cases', responding very well to insulin administration; others prove to be more challenging. Recent studies have shown a significant proportion of problem diabetic cats to have underlying acromegaly (hypersomatotropism). Recognising this syndrome in these cats will be key to successfully managing the concurrent diabetes.

PATIENT GROUP

Just like the 'normal' (non-acromegalic) diabetic cat, the acromegalic diabetic cat tends to be a middle-aged to older male neutered domestic short hair. However, with increasing case experience, this signalment may change. Most patients are insulin resistant, although this may not be the initial presenting sign. No breed predispositions have been recognised to date.

CLINICAL CHALLENGES

There is no single diagnostic test for feline acromegaly - a confident diagnosis relies on a combination of clinical signs, feline growth hormone and insulin-like growth factor 1 levels, and intracranial imaging. Additionally, the ideal treatment protocol has yet to be established. Currently, radiotherapy is considered by many to be the best treatment; however, costs, the need for multiple anaesthetics, and the often delayed and unpredictable treatment response represent serious limitations of this modality. Previously, medical treatment has proven unsuccessful. Recent studies provide some evidence in favour of, and some against, the use of newer long-acting somatostatin analogue preparations in a proportion of acromegalic cats.

EVIDENCE BASE

Two recent studies have revealed a relatively high prevalence of acromegaly among diabetic cats. One also specifically assessed the value of hormonal tests, computed tomography and magnetic resonance imaging during the diagnostic process.

Unusually rapid growth and adult stature in an American hairless terrier puppy

A puppy was evaluated for rapid growth and large stature. Extensive diagnostic evaluation suggested a growth hormone independent disorder. As the sole detected abnormality was elevated leptin concentration, an obesity syndrome causing leptin resistance was speculated to explain the puppy's condition but was not confirmed. Except for large body size, the puppy remained clinically normal.

Cryohypophysectomy used in the treatment of a case of feline acromegaly

A 10-year-old female spayed cat was diagnosed with acromegaly secondary to a pituitary tumour. At the time of diagnosis, the cat had insulin-resistant diabetes mellitus and its insulin-like growth factor-I levels were elevated. Clinical signs included polyuria, polydipsia and weight gain. Persistent hyperglycaemia and glucosuria were identified, and fructosamine levels remained elevated. Magnetic resonance imaging of the brain showed a pituitary tumour. Transsphenoidal cryohypophysectomy was used to treat the pituitary tumour. Postoperatively, the serum insulin-like growth factor-I levels decreased and the diabetes mellitus was controlled with routine levels of insulin. To the authors' knowledge, this is the second reported case of acromegaly treated with cryohypophysectomy, and the first that reports a favourable long-term outcome. Cryohypophysectomy may be a safe and effective treatment for cats with a pituitary mass resulting in acromegaly.