Cat with diabetes mellitus and acromegaly

It is currently assumed that up to 80% of cats sufferfrom a type 2-like diabetes. Other specific types (formerly called secondary diabetes mellitus) may occur in approximately 20% of diabetic cats.

Introduction

They develop as a sequela of another disease, the most important of which are pancreatitis, hypercortisolism and hypersomatotropism (acromegaly).

Diabetes may also be drug-induced (glucocorticoids, progestins). The presence of those diseases should be considered in cats in which regulation of diabetes is difficult.

Case Report

A 10 year old Domestic Shorthair cat (male castrated, 5.3 kg) was referred because of difficulties to regulate diabetes mellitus which had been diagnosed 3 months previously. Therapy had been started with Caninsulin® 1.5 U BID and highprotein-low-carbohydrate diet (Purina DM Dietetic Management®).

The insulin dose was increased stepwise to 6 U BID without clinical improvement. A change to Insulin Lantus® (5 U BID) was also unsuccessful. All technical aspects of insulin handling and injection had been checked by the veterinarian before referral. Physical examination in our hospital revealed slight prognathia inferior and was otherwise unremarkable (Fig. 1).

Blood glucose concentration at admission (2 hrs after injection of 5 U Insulin Lantus) was 25.5 mmol/l (4.0-9.0) and fructosamine was 581 μmol/l (200-340). Abdominal ultrasonography revealed increased liver size and increased echogenicity, bilateral renomegaly and bilateral adrenomegaly.

The liver findings were thought to be consistent with fatty infiltration caused by diabetes; main differential diagnosis for renomegaly were lymphoma, amyloidosis, FIP and hypersomatotropism, main differential diagnosis for adrenomegaly were hypercortisolism, hypersomatotropism, hyperaldosteronism and lymphoma.

Dr. C. Reusch

FIP, lymphoma, amyloidosis and hyperaldosteronism were considered to be less likely based on the facts that the cat was clinically well and BUN, creatinine and electrolytes were normal. Therefore work-up for hypercortisolism and hypersomatotropisms was pursued.

The results of the dexamethasone test (using 0.1 mg/kg dexamethasone) came back as normal, however, IGF-1 was highly elevated (> 1600 ng/ml; reference range 200-800). IGF-1 is a surrogate for growth hormone measurement and a high level is consistent with hypersomatotropism.

Since false positive results may occur diagnosis should be confirmed by CT or MRI of the pituitary gland (Fig. 2). The owners were informed about our findings and the therapeutic options, however, they decided against radiotherapy as well as against hypophysectomy.

The referring veterinarian continued insulin therapy and increased the dose of Lantus® to 15 U BID over the course of a few months. After 1½ years the cat became weak and the owners opted for euthanasia.

Comment

Hypersomatotropism in cats is caused by a growth hormone (GH)-producing tumor in the pars distalis of the pituitary gland. GH has catabolic and anabolic effects; the latter are in part mediated by IGF-1.

The catabolic effects are mainly due to insulin antagonism and are the reason for the development of diabetes. The anabolic effects include proliferation of bone, cartilage, soft tissue and organs resulting in a large body size, broad head and large paws, weight gain, prognathia inferior, respiratory difficulties because of thickening of pharyngeal tissues, degenerative arthopathy and organomegaly withpotential organ dysfunction.

However, it should be noted that clinical signs may also be very subtle (as in our cat) or even absent. According to recent studies acromegaly seems to be more frequent in diabetic cats than previously thought.

Dr. C. Reusch
SEVC 2012 Speaker

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