If you had to get a test, would you prefer to spend all afternoon in a hospital, or be home in time for lunch?
Elisabeth Ng, endocrinologist and PhD candidate in the Endocrine Hypertension Group at The Hudson Institute of Medical Research, knows the answer. That’s why she’s testing whether a simple scan can replace a complicated specialist procedure in the hunt for a hormone-producing tumour.
For patients with primary aldosteronism, Dr Ng’s research could be the difference between spending six hours in awkward small talk with a radiologist, or getting out in time for bottomless brunch.
Primary what?
Primary aldosteronism (PA for short) looks like regular high blood pressure, but it’s actually caused by a hormonal imbalance.
Once thought rare, endocrinologists now know that it’s behind 1 in 7 cases of high blood pressure.
It happens when small tumours on your adrenal glands start pumping out a hormone called aldosterone. Aldosterone isn’t just hard to pronounce – it’s also hard on your body, as one of its main functions is to tell the kidneys to retain extra salt and water. This excess salty fluid cranks up the pressure throughout your entire cardiovascular system.
Normal blood pressure drugs don’t work very well, because PA isn’t a normal case of high blood pressure.
Instead, doctors need to test the adrenal glands to find out which one is doing the dirty.
However, this test takes hours, is technically difficult, and not many people are qualified to run it.
This means it can take half a year to even get an appointment for a test, and is why endocrinologists are looking into quicker, easier alternatives.
Adrenal vein sampling – easier said than done
Since people have two adrenal glands, there are three possible places the tumour could be: in the left one, in the right one, or in both. If one gland is dodgy, it can just be surgically removed and the other one will pick up the slack. But if both glands are on the fritz, they need to be managed with medication.
As the name suggests, adrenal vein sampling (AVS) takes samples from the veins of the adrenal glands. This helps doctors figure out which gland has the problem and what to do next.
“They’ll put a cannula [a small tube] in through the femoral vein in the groin,” explains Dr Ng, “then thread it up to take a blood sample from the adrenal glands to measure aldosterone. This can provide a functional assessment of which gland might be overactive, or whether it’s both glands.”
Getting to the left adrenal gland is pretty straightforward – it’s basically a straight line. But the path from the groin to the right adrenal glands has a notoriously tricky turn. It takes an experienced radiologist to navigate the path, and the whole procedure can take a few hours as the maze is delicately navigated.
Unfortunately, there’s a shortage of radiologists who are trained and experienced enough to perform AVS skillfully. This isn’t because it isn’t fun, but because it isn’t funded – it takes a lot of time and a lot of specialist training to be able to do AVS properly, and radiologists could just earn the same amount of money doing faster, simpler procedures.
How a PET on your lap could lend a hand with the scan
Dr Ng thinks an existing test, called a PET scan, could be used instead of adrenal vein sampling.
“A PET scan is a nuclear imaging scan where you are given a small amount of a radioactive substance, called a radiotracer. These are designed to accumulate in a type of tissue that is of interest in the condition being investigated.”
“In the case of primary aldosteronism, we’re using the PET scan to try to see if it will light up the tissue that is overproducing aldosterone.”
There’s lots of radioactive substances that can be used in a PET scan, and different ones are good for different jobs.
“For example,” continues Dr Ng, “certain PET scans can be used to diagnose and monitor cancer. FDG-PET uses the radiotracer FDG, which is similar to glucose and is taken up readily by rapidly metabolising cancer cells. FDG-PET allows us to see the presence and location of metabolically active tissue such as cancer cells.”
The next step is to find the particular kind of tracer that’s best at detecting aldosterone-producing growths.
“Researchers in this field are exploring several different PET tracers, and the goal is to work out which is the most selective for adrenal aldosterone-producing adenomas, but is also logistically feasible and affordable.”
“Identifying a tracer that will consistently be taken up by the adrenal tissue that is overproducing aldosterone would allow us to direct people to targeted treatment promptly and without having to wait for and undergo adrenal vein sampling”
Bigger country, bigger problems
Much of the research so far has taken place in England and China, where the healthcare systems work a little differently.
The big thing about Australia is its incredible bigness. Our cities sprawl out for hundreds of kilometres, our hospitals are far apart, and if you live out the back of beyond, a hospital test usually means packing your slippers for an overnight stay.
This distance also means we have to use different tracers than other countries. Being radioactive, tracers start breaking down within hours, so they need to be used quickly. There’s only a few particle accelerators in Australia that can make these tracers, and once they’re created they have to be rushed to hospital.
Countries with shorter commutes or more particle accelerators don’t have this problem, but Australia is a large country and the tracers have to survive a long commute. That’s why Dr Ng’s team is testing a particular kind of tracer that can survive an Aussie road trip.
Testing patients, not patience
As well as looking into PET scans, Dr Ng is also working on an algorithm that could predict who needs surgery and who needs medication. This means that hospital tests might only be needed for the really tricky cases.
If Dr Ng’s research pans out, patients with primary aldosteronism might soon be swapping long afternoons of adrenal spelunking for a quick lie-down.
A reliable PET scan for aldosterone-producing adrenal growths could mean faster and more reliable diagnoses, and less pressure on the handful of radiologists who know their way around an adrenal vein.
