Evidence and stroke

If you’re in New Zealand, there’s a good chance you’ve seen the Stroke Foundation’s new TV ad campaign describing how to recognise a stroke and what to do about it (get the person to hospital Right Now). I often criticise the evidence behind health stories in the news, so it’s worth looking at how different this is.

A Herald story says

Up to half of all stroke cases could be treated with clot-busting drugs if they arrived within three hours of the stroke’s onset at a hospital.

That’s a little optimistic. There are basically three categories:

• strokes caused by bleeding
• strokes caused by clots, where the brain cells haven’t had time to die
• strokes caused by clots, but where the brain cells have had time to die

In the second group, dissolving the blood clot is helpful — it reduces the risk of both death and disability. In the first group it’s definitely harmful, and in the third group it’s unhelpful and risks triggering bleeding. 

If you get a stroke victim to hospital fast, there’s a good chance of getting them through emergency-room triage and diagnosis, and into a CT scan that can distinguish between groups one and two before it’s too late. But even if you react quickly, that’s a lot of things that have to go right — and a lot of them have to happen after you get to hospital.  The current NZ stroke guidelines say that treating 20% of cases is a realistic target: a bit less than half of those who could benefit in a perfect world.

So, how do we know the treatment is helpful, and for whom?  As with clot-dissolving treatment for heart attacks, this isn’t easy.  In particular, it’s fairly obvious which patients are harmed by treatment — they end up with bleeding in their brains — but it’s much harder to tell which patients are helped, and by how much.

The only solution is randomised trials, where patients were randomly assigned to clot-dissolving drugs or the standard treatment.  These trials need careful design, both practically and ethically. You’re introducing new diagnosis and treatment steps into over-stressed hospital emergency rooms; you’re using a treatment that might be life-saving or lethal; you’re targeting people who (by definition) don’t have their brains in good working order.  The trials were done: we now have 27 trials in 10,000 patients, and clot-dissolving treatment does more good than harm — unambiguously, if started within 3 hours from the start of symptoms and probably somewhat later, but not the next day.

In terms of evidence, this isn’t at the levels of getting vaccinated and stopping smoking, but it’s miles ahead of the evidence around fish oil or vitamin supplements or coconut oil or kids these days and their phones and internets.