Acromegaly in Cats: 3 Clues and the IGF-1 Timing Rule

Acromegaly in a cat rarely announces itself. The first 3 clues are metabolic and easy to miss: a diabetic cat whose insulin need creeps up every 3 to 6 months, a cat that starts snoring at 8 years old, and a jaw or paw that looks wider than it did 2 years ago. The tumor behind all 3 is a slow pituitary one, and the screening test — IGF-1 — is only as good as the 4 timing rules behind the sample.

Clue 1: insulin that stops working

Most cats are 8 to 12 years old when the diagnosis is made, and most arrive with diabetes already on board. The pattern worth flagging is not a high starting dose but a dose that keeps climbing: 2 increases inside 6 months, or an insulin need that passes roughly 1.5 units per kg per injection with no change in diet or body weight. At that point the working list holds about 12 entries, and acromegaly sits near the top because growth hormone blocks insulin at the muscle.

Pull 3 things from the same visit: a 12 hour blood glucose curve, a fructosamine, and the weight trend over the last 6 months. A cat that gains 0.5 kg while glucose stays above 300 mg/dL is a different case from one that loses 0.4 kg on the same curve.

Clue 2: the head, the paws, the snore

Bone and soft tissue both grow, slowly. Measure instead of eyeballing: jaw width at the widest point, paw width across the 4 toes, and body weight at every visit, written on the same line of the record. A 3 to 5 mm widening of the jaw over 12 months earns a note. Snoring that starts after age 7, or a cat that sits with its mouth open at rest, points to soft tissue thickening in the throat and around the larynx.

Photograph the head straight on, 3 times a year, from the same distance. Owners spot a 4 mm change in a photo faster than in a mirror.

Clue 3: heart and airway together

Growth hormone enlarges the heart, the thyroid and the kidneys. A murmur first heard at 9 years old, a systolic pressure above 160 mmHg, a resting respiratory rate above 30 breaths per minute at home, or a thyroid nodule found on a 2 minute neck check all belong to the same picture. Cardiomyopathy and acromegaly overlap often enough that an echocardiogram is a reasonable second step, not a third.

Weigh the cat on the same scale, at the same time of day, every 8 to 12 weeks. A 10 percent gain in 6 months with no diet change is the cheapest screening tool you already own.

The IGF-1 sample: 4 timing rules

IGF-1 is a single serum sample, and it is far more fragile than it looks. Rule 1: draw it fasted, 8 to 12 hours after the last meal, because a recent meal shifts the reading. Rule 2: use one laboratory for every sample, because upper limits differ by roughly 20 percent between assays and a switch mid-case makes the trend unreadable. Rule 3: wait until the cat has been on a stable insulin routine for at least 3 to 4 weeks; a cat in poor glycemic control can read falsely low. Rule 4: if the first result sits near the cutoff, repeat in 4 to 6 weeks before imaging.

Keep the draw at the same hour each morning, before the injection, and note the hour on the form.

What the numbers look like side by side

Clue	What to measure	Flag value	Recheck
Insulin resistance	Dose trend over 6 months	2 increases, or above 1.5 U per kg per injection	Every 3 months
Jaw and paw width	Calipers at the widest point	3 to 5 mm wider in 12 months	Every 6 months
Airway noise	Resting breaths per minute at home	Above 30 per minute	Daily for 7 days
Blood pressure	Doppler, 3 readings averaged	Systolic above 160 mmHg	Every 3 to 6 months
IGF-1	One fasted serum sample	Above the lab limit, often near 1,000 ng/mL	8 to 12 weeks after any change
Pituitary imaging	CT or MRI, 2 mm slices	Mass above 4 mm	Every 12 months

What a normal IGF-1 does not rule out

A cat with a small pituitary mass, a cat tested 2 weeks into insulin therapy, and a cat with untreated severe diabetes can all read inside the reference range. If the 3 clues are present and IGF-1 is normal, the next step is not reassurance, it is a second sample in 6 to 8 weeks plus a pituitary scan. The reverse also happens: a high IGF-1 in a cat with no clinical signs is a reason to keep measuring every 6 months, not to treat.

Also check the kidneys and the heart before any imaging. A creatinine rise, a urine protein to creatinine ratio above 0.4, or a heart murmur changes the order of the workup, because anesthesia for a scan carries its own 1 in 100 to 1 in 200 risk in an older cat. A rising kidney value is the commonest detour, and the 2 tests that sort out early kidney signs explain why the recheck is at 3 months, not 12. The cost calculator covers what a scan adds to the bill before you book it.

Emergency thresholds: go now, not next week

Some numbers do not wait for a scheduled recheck. Blood glucose below 60 mg/dL with wobbling, staring or a seizure is an emergency; so is glucose above 400 mg/dL with vomiting, ketones in the urine, and a cat that stops eating for 24 hours. A resting respiratory rate above 40 breaths per minute, open mouth breathing, or gums that look grey rather than pink mean the same thing. Systolic pressure above 180 mmHg with sudden blindness is a same day appointment. Do not wait for the next curve, and do not adjust insulin at home to buy time. A cat that squats 10 times an hour and passes nothing is a second emergency hiding behind the first; urinary blockage signs lists the 3 signs that mean the bladder is already closed.

Your next 7 days

Weigh the cat on one scale and write the number, with date, in a single note.
Count resting breaths per minute for 3 days, twice a day, while the cat sleeps.
Photograph the head and front paws from 2 fixed positions, same distance.
Book 1 visit that covers a 12 hour curve, fructosamine, blood pressure and a fasted IGF-1.
Ask for the lab's upper limit in writing, so the next sample can be compared to it.

Nothing here treats the tumor. Treatment options are prescription-only and chosen by a vet after imaging: surgery in a handful of centres, radiation, or medical control of the growth hormone axis. What an owner controls is the timing of the sample and the quality of the trend, and those 2 things decide how early the case is caught.

Terms mentioned in this article

Frequently asked

Can a cat with acromegaly have a normal IGF-1?

Yes. A small pituitary mass, a sample drawn in the first 2 weeks of insulin therapy, or poorly controlled diabetes can all push the reading into the reference range. If the 3 clues are present, repeat the fasted sample in 6 to 8 weeks and ask for pituitary imaging rather than accepting the normal result.

How long before a recheck should the cat fast?

Plan on 8 to 12 hours without food, and keep the draw at the same hour of the morning each time. Water stays available. Use one laboratory for every sample so the upper limit does not move between visits, and write the draw time on the form.

When is acromegaly an emergency?

Glucose below 60 mg/dL with wobbling or a seizure, glucose above 400 mg/dL with vomiting and ketones, 24 hours without eating, a resting respiratory rate above 40 per minute, or systolic pressure above 180 mmHg with sudden blindness. Each of those needs same day care, not a scheduled curve.