Imaging of patients with headaches

MRIs are wonderful, they're almost the neurology handshake for us, but they do have some limitations, and I guess the most important caveat to start with is the delay in access to the scan. 

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Headaches are very common, and are one of the top 20 reasons that Australians visit their GP each year. For new, persistent, or severe headaches the question of whether or not imaging of the brain is necessary to find out the diagnosis is basically front of mind for patients and GPs alike, if you'll excuse the pun. My name's Dr Laura Beaton, I'm a GP in Melbourne, and your host for this episode. To talk through this problem I'm joined by Dr Jason Ray, neurologist and headache subspecialist at Alfred Hospital, Austin Hospital, and Monash University, to discuss his article “Imaging in Headache Disorders”, in Australian Prescriber. Welcome to the podcast, Jason. 

Thank you for having me. 

Given that headaches are such a common symptom, and it does have some rare and serious causes, it's not surprising that we are commonly faced with the question, do we need to image this person's brain to find out what's going on? Or can we be reassured by good history and a thorough clinical examination alone? Could you please take us through the steps that you take when evaluating if imaging is needed for somebody who's presenting with headache? 

It's a really good question. I suppose for myself it's divided into times when I feel imaging is required for my sake, or for clinician factors, or for the patient's sake, or patient factors, and it's really important to identify what we want to investigate for, or what we want to reassure against. For the clinician we're really looking for the patient that doesn't fit the mould, either because they have an abnormal finding on examination, the presence of red flags on history for a secondary headache disorder, and in our article we summarise a clinical evaluation really into the five Ps, so patient factors, the pattern of the headache, the phenotype of the headache, precipitants for the headache, or any abnormal pharmacology, along with the red flags. 

For the patient, when they're coming to see their specialists, be it GP or neurologist, they're looking for reassurance that the often excruciating pain that they're experiencing isn't actually causing damage to the brain, or that it doesn't represent a sinister pathology. And often with a careful history and an explanation we can provide that reassurance clinically. Some patients though then require that further reassurance with neuroimaging, and that's not in and of itself unreasonable, but it is important to contextualise that discussion to make sure that we're both addressing the patient's concerns to avoid unnecessary or serial imaging, but also forewarning against the potential for incidental findings. 

Headaches are something that we commonly see in general practice, but it's not something that comes in, as every single thing, like say in a headache clinic in a tertiary service. We know that mnemonics can be pretty helpful when you're remembering important facts that you need to pull from your memory quite rarely, but quickly. Can you take us through the SNOOP4 list that you present in the article, which is about the red flags when you're considering secondary causes of headache. 

The SNOOP4 list is a validated list that help exclude for secondary headache, being a headache where the pathology is coming from something else, so be that meningitis, a stroke, or anything else, and it's a useful thing to be able to reach for if, it's not something which you're going for every day. And so the S stands for systemic symptoms, so for fever or weight loss, which is obviously worrying for meningitis or malignancy, either primary or secondary. The N for a neurological deficit, so obviously focal neurological deficits in the setting of a headache is very concerning for either a new stroke, a space-occupying lesion, hydrocephalus, amongst others. The first O is for the onset of the headache, so a thunderclap or a very abrupt onset headache is very concerning and needs a referral to the emergency department for a subarachnoid haemorrhage, but even after that's been excluded there are other differentials for a thunderclap headache, such as pituitary apoplexy, reversible cerebral vasoconstriction syndrome, venous sinus thrombosis. 

And the second O is for older age. So a new headache disorder in a patient over the age of 50 is atypical, and the patient needs to be investigated for either malignancy or giant cell arteritis. And then because no medical mnemonic is perfect we squash four Ps in towards the end of it, and the last four Ps are for the position, so a new onset headache, or a headache which is precipitated by a change in position, or by coughing, sneezing, or anything which brings on a Valsalva reflex, is concerning either for high or low pressure in the brain, or a lesion in the posterior fossa, so right at the back of the brain, which could be intermittently obstructing, or just a change in pattern of the headache. 

It's always fun to talk through mnemonics, I have many that I remember from medical school days, and many I still pull back out again. And I think when we were going through that SNOOP4 list, and then going back to what we talked about before, about the clinical evaluation, thinking about the patient factors, the pattern of the headache, the phenotype, we really covered off lots of those serious causes of headache in those red flags, and then I wanted to talk a little bit about the other two, the precipitants and pharmacology as part of the clinical assessment of a headache history. And so when you're talking to someone about their headaches, what are the key medications that you ask about when evaluating their headache?

Unfortunately, when we go for the side of a product information sheet on any medication, or when a patient goes for the side of a product information sheet for any medication, headache is invariably listed. So there's a lot of medications which it probably isn't such an issue, but it is worth taking a careful history and just looking for a temporal relationship, but there are several medications which really are notorious for causing headaches. These include tacrolimus, so the calcineurin inhibitors in patients who've had a solid organ transplant. Interferon beta, which is one of the older multiple sclerosis medications, which happily not many patients in Australia will be on anymore. And nitric oxide donors, phosphodiesterase inhibitors, some of the antidepressants and cyclosporine. And then there are some other medications such as the tetracyclines like doxycycline and vitamin A analogues, that don't themselves cause headaches, but can in some patients raise intracranial pressure, and so increase your risk of other conditions such as idiopathic intracranial hypertension, which will itself present with a headache. 

One of the things in your article you also mentioned was medication overuse, and so not just of triptans or opiates, but also of simple analgesia. Can you talk through how you talk to patients about their use of regular analgesia for chronic headache conditions and how you evaluate that when talking about their headaches? 

I find that this can be a quite sensitive topic to discuss with patients, and it's really important to differentiate the idea of addiction to a pain killer from medication overuse headache because they're not the same thing, and we're not talking to patients in the same context as somebody who unfortunately suffers from opiate addiction syndrome, or who has another issue. Medication overuse headaches are unfortunately something which particularly patients who have migraines suffer from, and once you start to have chronic daily headaches up to 70% of people will have as a comorbidity, and the threshold to which you need to take a pain killer before it starts to cause this varies with the class. So for simple analgesics it's about every second day, and for the triptans and the opiates it's 10 days in a month. 

And the effect of the medication overuse is that they reset the normal in the pain system of the brain. So the endogenous inhibition of the pain system in the brain gets reset because we're constantly giving it painkillers, and so whilst the painkillers still work, they work a little bit less, but also you start to get, it's almost a rebound headache that keeps coming back, unfortunately in the long term, because of the constant exposure to the painkillers, and unfortunately a lot of our migraine preventative medications work a little bit less to it, and under the PBS rules we're actually a little bit limited in terms of what we can give to people until we address it as well. So it's much easier to avoid in the first place there, and there are good strategies for treating it once we have it, but much better to avoid in the first place. 

Yeah, I agree. And someone's medication history is part of the context that they are existing and presenting in, and you go through some other key precipitating factors that you would ask about as well as part of your evaluation of headache. 

Yes, and we've already discussed a couple of them in terms of precipitation of a headache in terms of change in posture, straining and Valsalva. The other key things that I'll often ask patients when I'm taking a headache history is whether the headaches are only occurring in the setting of a particular trigger, or are task-specific headaches such as exertion, intercourse or sleep. So a headache which, for example, in the setting of sleep only occurs early in the morning, resolves within 30 minutes of getting up, particularly if it's occurring in the setting of disrupted sleep, could be worrying for something such as obstructive sleep apnoea, which needs to be investigated in its own right. And headaches which are brought on in the setting of exertion can be a rarer form of headache called cardiac cephalgia, which is akin to neurology's version of presentation of cardiac angina, and for some patients, if a patient has vascular risk factors, it may be the only warning that they have that they may be in line to have a heart attack, so it's important to recognise those patients, although they are rare. 

What are the reassuring signs, or green flags, I guess as we call them, for a headache, when you think, look, for this person, probably imaging could safely be avoided?

And I guess to preface this, as opposed to the red flags for headache, which have been around for quite some time, this isn't validated. The green flags for headache arose from polling the headache subspecialists from around the world, and they did it using the Delphi method, or almost like the French electoral method, they asked them all what would be a reassuring factor for you? And then polled the answers, and then sent all of the answers back around again and again, ranked them again, and they came up with the highest ranked answers, or the French president. And they came back with four answers which I think intuitively make a lot of sense, and themselves very reassuring things for me as well when we take a history. And so obviously this is only true for adults, but the first of them is that the current headaches, or the headaches that patient is presenting to you with, have been there since childhood, and the rationale slightly morbidly being that if it was going to be something serious it should have presented itself as such by now. 

The second is that the headache is temporally related to the menstrual cycle, and obviously menstrually related migraine is a very common feature of migraine, and so the probability of that patient having migraine is much higher. And the third is that the patient has headache-free days, and the rationale for that is that most of the primary headache disorders are intermittent, whereas most secondary headache disorders, with the notable exception of brain tumours, are less common to have headache-free days, and so secondary causes are much less likely in that setting, and they're also less likely to be associated with an identifiable trigger such as food or exercise, well not so much exercise, but a dietary trigger, for example. And the final is that there's a close family history of the same phenotype of headaches, so obviously family histories of migraine are very common, and so a presence of such is reassuring from that perspective. 

And if we do decide that imaging probably is necessary, either from a clinician's perspective, or considering other patient factors, MRI’s the modality of choice, and I guess GPs can request this with an MBS rebate for a few indications, for unexplained seizures, unexplained chronic headache, or a suspected intracranial pathology, which lines up to some of the really big red flags for a secondary headache. And I guess you already touched on this before, but what are the potential downsides or limitations for ordering MRIs for headache? 

MRIs are wonderful, they're almost the neurology handshake for us, but they do have some limitations, and I guess the most important caveat to start with is the delay in access to the scan. So some of the red flags that we discussed are emergent conditions, or they suggest potentially emergent conditions, or the patient has new focal neurological deficits, they're systemically unwell, they've got a thunderclap headache, they can't be sent for an outpatient MRI, they need to be assessed in the emergency department in the first instance. In that instance an MRI's not the most appropriate test. 

Secondly, unfortunately there's no standard set of sequences that a radiologist will do for us that will answer every potential question that we could possibly have for an MRI. For example, in a given clinical scenario, if you're particularly concerned, for example, of a venous sinus thrombosis, or a pituitary lesion, or a cerebral arteritis, those would all required very different sequences on an MRI. So it's very important that we communicate clearly with our radiologists what we're most concerned about, so that the correct sequences are performed, or if we're seeing the patient after the fact that we go back and look and see that those sequences were performed so we're not falsely reassured just from the fact that they had the MRI. 

And finally, aside from what we may miss, the other downside of an MRI is what we may find. And we alluded to it before, in a general population 2% of patients will have an incidental finding on an MRI which can lead to further investigation, utilisation of healthcare resources, but most importantly the resultant worry and stress for the patient and their families. 

One of the other things you touched on there was these common, incidental findings, incidentalomas, not the bane of my existence, but they are a very common thing, seek and you will find. And I guess for many patients I found that actually the need for reassurance that this isn't a brain tumour vastly outweighs the potential risk of, oh, I might find something else. Then when we find something else, then we open up another can of worms, shall we say. Can you give us an example of how you might explain to a patient who's quite anxious to exclude something like a brain tumour the risks of finding incidentalomas? 

For most people, I'm happy to give them an MRI for the reassurance value that it will provide, with the caveat that we discuss that oftentimes we're going to find something else for these reasons, this is why it is a migraine, and we agree at the outset what it is so that when we come out and we find the other things that they're going to necessarily find, be it particularly relevant for the migraine population, there'd be small Chiari malformations, or there'll be a small arachnoid cyst, which are present in about half a percent of the population, and can be irrelevant in a patient presenting with a headache in the right clinical circumstance, that they're the ones that most worry me as a clinician because they can really muddy the water and they can really take you down a very different path if a patient then starts to worry, is that now causing my headache?

And so they're the conversation that I most want to preempt when I'm having that, and then of particular relevance to patient with migraines is the finding of white matter lesions, which is unfortunately not uncommon, and they're sometimes unfortunately ambiguously reported, there's concern for demyelination, and that in and of itself as well can cause a great deal of distress for patients and their families. And so it's important to have a little bit of a process for how to approach that conversation when that comes up as well. For myself, obviously there are radiological features that will help us differentiate demyelination from migraine, and some of these we do need to refer on and follow up longitudinally, but the white matter lesions that we do see in migraine, they occur in 5% of people, they're not associated with anything untoward in terms of later cognitive decline or onset of dementia, or even further disability with regards to the disease, and so I personally, when I'm having the discussion, will liken it to freckles on the brain for a patient, which sounds a lot better than white matter lesions. 

That's a very helpful analogy, thank you. It's been really great to go through this article with you and think about all those times when imaging is really essential for either ruling out serious intracranial pathologies, and also for patient factors as well, and then also consider the times when we can safely avoid imaging. I really appreciate you taking the time to take us through this today. 

Thank you so much for having me. 

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Jason Ray has received compensation from the Pharmaceutical Society of Australia, sponsored by the Viatris for educational material. The views of the host and the guest on this podcast are their own and may not represent Australian Prescriber or NPS MedicineWise. See you next time.