Monday, January 02, 2006

CAT scans

Should you have a CAT scan as part of your diagnostic work up?

A CAT scan uses a computer to produce pictures of what thin slices through your body would show if you were put through a bacon slicer. There is no doubt that they have revolutionized the practice of medicine. When I was a lad the abdomen was a mystery. You could feel things with your hands through several layers of flesh, and you could try to figure out what they were by tapping, listening, ballotting and guessing. X-rays were pretty hopeless, and frequently we resorted to opening it up to have a look. The chest was easier - the stethescope allowed you to listen to snaps, crackles and pops coming from the heart or lungs and chest X-rays showed shadows that could be interpreted by some. The pelvis could only be examined by sticking your finger in various orifices. Pity those with short fingers. What went on inside the head had to be guessed at by very indirect signs. Neurologists were the super-diagnosticians, able to deduce a diagnosis from the merest hint of an absent knee jerk. Of course, they had no treatments; that would spoil the fun.

Then came the CAT scan and most people gave up on clinical signs. You could see what was happening; you didn't have to guess. Head scans revealed a wonderful picture of the brain. Neurologists nowadays ask for a CAT scan first before offering an opinion, and if you already have one they ask for an MRI. I have a colleague who is whizz at chest CTs. Listening to him demonstrate a case opens new vistas of understanding. I am most used to abdominal scans. You can get a clear picture of abdominal glands in the lymphoid tumors.

The problem with CAT scans is the amount of X-irradiation they use. Radiologists used to joke that they were no longer mere diagnosticians; with the amount or radiation a patient received they could now be thought of as radiotherapists. They were exaggerating, but there is certainly a concern that too many CAT scans can damage your health.

The public's attitude to radiation seems to go through phases. Immediately after World War II there was a nuclear hubris. The atom bomb had won the war and everybody wanted the benefits of X-rays. They even had X-rays in shoe shops to see that your shoes weren't too tight. It was interesting that President Eisenhower couldn't pronounce 'nuclear' - it came out as 'newcular' and several American Presidents have followed suit.

Then came the nuclear disarmament movement, generously funded from the Soviet Union and many people turned against anything nuclear. Then Three Mile Island, and especially Chernobyl really put the hoodoo on the whole nuclear question. In the UK we rejected irradiated food, even though it was quite harmless and wouyld have saved thousands of cases of food poisoning. Now with greenhouse gases, global warming and Russian gas supplies cut off, nuclear power stations are back on the agenda.

As with most things radioactive, the risk of CAT scans is greatly exaggerated, but there is a risk and they should be used sensibly.

Are they of any value in CLL?

The first thing to say is that staging of CLL does not involve a CAT scan. Lymph node enlargement only counts if you can feel it with your hand. An enlarged spleen is not enlarged unless you can fel it below the ribs. It's the same with the liver. If you started to stage according to the CAT scan, then patients who are stage O would be called stage I or II, and the prognosis of stage I and II would be much better than we think it is. All the rules on how to treat it would have to be changed. So for staging CAT scanning is out.

There are moves afoot to make CAT scanning part of the work-up for patients entering clinical trials, and I can see the merit in this. Watch this space.

I think that patients with unexplained symptoms who appear clinically to have early stage disease should have a CAT scan. It could reveal much more extensive disease than had been imagined and would add to the understanding of what is going on.

So the answer is - as a screening test, I would not advise CAT scanning, but to investigate unexplained symptoms then it is a useful test.

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