An underestimated population of diabetic cats seems to have a non-traditional explanation for its condition: feline hypersomatotropism (HST). In fact, a study published in 2015 from UK estimated as many as 25% of diabetic cats in the UK to have HST.
What is hypersomatotropism and how does it compare to traditional type 2 diabetes?
Hypersomatotropism (HST) is characterized by excess growth hormone (GH) production due to a tumor of the pituitary gland. The tumor itself is typically non-cancerous, but excess GH production and secretion have consequences, such as insulin resistance and glucose intolerance. In fact, it has been reported that most cats with HST eventually develop diabetes mellitus, and show compatible signs, including increased urine output, increased thirst, and excessive hunger.
Despite such similarities, HST shows distinct clinical signs. The clinical syndrome that arises due to HST is known as acromegaly. These include broad facial features, clubbed paws, protrusion of the mandible, and enlarged tongue that is typically presented by snoring. Imaging scans, or sometimes palpation, can reveal enlarged abdominal organs. Cardiac abnormality, such as a heart murmur, is another sign more common in HST.
How is it diagnosed?
Unfortunately, the actual presentation rate of these HST-unique physical signs seems to be low in real-life cases. Since traditional type 2 diabetes mellitus and HST-associated diabetes also overlap in many areas, the latter can be easily overlooked in diagnosis. Still, one of the most common indications for pre-test suspicion is known to be severe insulin resistance. Many cats appear to have poorly-controlled diabetes despite being treated on a normal dosage of insulin therapy. They require subsequently greater doses to achieve glycemic control.
Currently, the most widely used diagnostic tool for HST is serum IGF-1 concentration. A study showed serum IGF-1 concentration of >1000ng/mL to be a powerful indicator of the presence of HST in its study pool, with a 95% positive predictive value. All suspicions are to be confirmed with a CT or MRI imaging that reveals an abnormal enlargement of the pituitary gland.
Does it have different treatment options?
The management options for HST-associated feline diabetes can be largely categorized into two types: conservative and aggressive therapies. The goal of a conservative therapy is mainly glycemic control. It typically involves administrating larger doses of insulin, sometimes as many as 16 units twice a day. Conservative therapies, however, are not intended to prevent the progression of HST. In fact, many cats die of congestive heart failure.
Aggression therapies aim to address the problems of HST. Radiation therapy involves decreasing the tumor size. However, its effectiveness is not guaranteed and it will most likely require recurring treatments. Surgical removal of the pituitary tumor is rare and costly but its effectiveness is reported to be high. On the down side, it is accompanied by lifelong hormone supplementation. Potential drugs, such as the novel somatostatin receptor analog pasireotide, are still being studied for efficacy and safety. Given the differences of treatment options and prognosis in HST-associated diabetic cats, it may be valuable to have cats be evaluated should suspicions arise.