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Transcript
Thank you, and I want to thank the Spinal CSF Leak Foundation and Dr. Callen for inviting me to talk with you today about RIH – rebound intracranial hypertension.
So, we spent a lot of today talking about treatments and procedures, and even by the time we get to that treatment, I know we are all wishing that the journey would be over. But, like we talked about today, a lot of us at that point are then dealing with treating and managing RIH. To me, RIH is that tip of the iceberg – there is still a lot left to discover. And what I think is that the more we know about RIH, the more we’ll learn about SIH pathophysiology and how the body changes to compensate for leaks.
So, we talked a lot about knowns and unknowns, and it’s true – there are a lot of unknowns with RIH. Today, I’ll talk about what we know and what we don’t know about what is RIH, the different treatment options, and some of my thoughts on why there is variability in how people experience it.
So, what is RIH? Descriptively, it’s a change in symptoms due to increased craniospinal pressure that occurs following procedural treatment of SIH. And that could be epidural blood patching, CSF venous fistula embolization, or ligation, or surgical dural repair.
But what we don’t know, and what we really need, is a formal diagnostic criterion for RIH. Formal diagnostic criteria for RIH – and also a standardized process and standardized time points for assessing RIH symptoms can help us capture the true incidence of RIH. What we are currently estimating is that about a fourth of patients treated for SIH develop RIH, and there’s a female predominance, and it usually occurs in the mid-40s, which tracks along with the incidence of SIH. But what we don’t really know is why some people experience RIH and why some people don’t. It doesn’t seem that brain sag or pre-procedural opening pressure are risk factors for RIH.
Some of the risk factors we’ve found are that extensive extra-dural CSF collections, IIH, or a history of RIH or risk factor for IIH can be potential risk factors for RIH.
And while we’re still learning about individual risk factors, what do we know about how procedural type affects RIH? Again, this is also limited by a lack of formal diagnostic criteria and a standardized set of time points in which we assess for RIH symptoms. But there have been some several nice studies by the people who have talked here today. Dr. Schievink did a study that showed there is a slightly higher incidence of RIH in people who have undergone a surgical intervention as opposed to a non-surgical intervention. Dr. Beck found that about 36% of his patients after minimally invasive dural repair developed RIH. And Dr. Kranz found that there is no link to patch volume in the development of RIH. As Dr. Kranz mentioned earlier today, there is wide variability in the data that we have about RIH after CSF-venous fistula embolization.
I wanted to highlight this specific study that was done at Mayo Rochester that looked at 100 patients who had undergone CSF embolization, and they found out about 17 – or they at least tallied up 17 – of them who got RIH. What was really interesting is that it seemed to be that there was a treatment-dependent response to who got RIH, with the majority of people getting RIH and who did not have improvement in their SIH symptoms. So, what that suggested to me is that maybe there is something about that procedure that influences CSF hemodynamics.
Now, one of the most important aspects of RIH for both patients and their clinical partners is to recognize it. With RIH, we expect that there is a change in symptoms occurring within the first week of the procedure and resolving within about three months. And the classic – and I highlight classic – presentation of RIH is that it’s basically an inverse of SIH. So, the pain in SIH is mostly sub-occipital where the head and neck meet, whereas in RIH, it is more frontal or periorbital. In RIH, the pain is worse upright, and it’s worse in the morning after sleep. With RIH, people might also experience nausea, vomiting, blurred vision, and there are reports of even transient papilledema.
But, of course, clinical medicine is complicated, and it’s important to be aware of some features that make distinguishing SIH from RIH a little confusing. One of those things is that SIH may also not present typically. People with SIH can have frontal headache or headache in any location. They might also have paradoxical pain – pain that gets worse when they’re lying flat. There can also be a delay in some symptom development. So, I just mentioned that, a lot of times, in the majority of cases, RIH develops within that first week, but there are cases of people developing it after many weeks and even months.
There are times in RIH it presents with occipital pain or non-frontal pain, and there are also cases where RIH is actually presenting as back pain and not any change in headache location. So, it’s important to keep those factors in mind but also to keep an open mind if someone is having atypical symptoms of RIH, especially if they’re prolonged or refractory. We talked yesterday about cerebral venous sinus thrombosis – this is definitely on my high list of differential diagnoses for people who don’t have that classic presentation of RIH. So, I would encourage you to get a work-up for that.
The fortunate thing is that RIH does typically self-remit, but the symptoms, until that happens, can be quite debilitating. So, we often start off by treating people conservatively with head positioning and also maybe a low-salt diet, dandelion tea. Next steps – usually the gold standard is acetazolamide. That’s a really tricky medication to use, and it can have a lot of really harsh side effects. So, actually, I give my patients 125 mg of acetazolamide to take if they’re not really experiencing significant RIH symptoms. And then to titrate it up to kind of a gold dose of 250 mg to 500 mg, two to three times a day, and we can even titrate that up further if needed. And as the last speaker mentioned, sometimes we use alternative treatments too. So, methazolamide is a great option if someone can’t tolerate acetazolamide. Topiramate, furosemide, HCTZ, spironolactone – all of those could be used, and these are just a few from a list of medications that we can use.
CSF drainage or diversion – and I know I’m kind of preaching to the choir here – is only used as a last resort, so only if there are intolerable symptoms or diagnostic uncertainty. But there are also some very important treatment considerations that are not known, that are very interesting, and I hope that in a few years we’ll have answers to this.
So, first is, how does RIH truly impact healing? When I was starting out in this field, I was always told RIH is a good thing – you know, it’s great when we see RIH. But when we look at the cranial leak literature, they’ve actually found that aggressive treatment of ICP, of elevated intracranial pressure, after surgical repair is beneficial for people with idiopathic intracranial hypertension-caused cranial CSF leak. So, do we need to more aggressively treat RIH?
The other thing is, there’s no real standard pre-treatment protocol. Is that necessary? There is a study by Ferrante et al. that found that treating with acetazolamide at a dose of 250 mg at 18 hours and 6 hours prior to a large-volume, untargeted lumbar blood patch was very beneficial. So, if we’re kind of putting two and two together, if it is helpful for us to treat RIH aggressively, this might be something we consider – you know, maybe prevent the symptoms before they develop or become too severe.
Now, this is what’s really exciting to me is the pathophysiology. There’s no real clear idea of why RIH happens. There are a couple of different factors that are discussed in the literature. So, maybe there’s venous distension, changes in venous outflow, maybe there are changes in CSF reabsorption, there’s changes in dural compliance, maybe there’s underlying IIH.
I think many of these factors can actually link together under this concept of craniospinal elastance, which describes what pressure does in response to a change in volume. So, this is a nice graph here, and I know in the CSF leak field, we’re not strangers to the balloon analogy, so I’ll make no exception here. I want you to imagine a balloon, and you’ve only filled it up a little bit with air or water. You can still squeeze that balloon – it’s still pretty flexible. That balloon, in my analogy, is kind of at the lower end of that curve. Now, imagine that you’ve really filled up that balloon a lot with air or water, and you try to squeeze it. It’s become more rigid. It has more elastance and has become less flexible to any change in volume. In this curve, you can see that the higher up we go in terms of elastance, the same amount of volume increases the pressure so much more.
So, to truly understand RIH, we need to understand what affects craniospinal elastance. One hypothesis is that the veins in the craniospinal system are the key drivers of craniospinal elastance. Typically, the job of the veins is to buffer large changes in volume without significant increases in pressure. This can happen in normal pathophysiology. But in compensated spinal CSF leak – so people who have had a CSF leak for a long time or who are just very adaptive and resilient and compensate for it – it’s been shown that the epidural venous plexus becomes engorged, thought to be a compensatory mechanism, and that the outflow of the internal jugular veins is decreased. So the internal jugular veins collapse to boost up the pressure and again compensate for this lower pressure that’s happening in spinal CSF leak.
Dr. Schievink also did a really nice study which showed that narrowing in the veins is linked to an increased risk of RIH. So all of these compensatory changes can increase venous elastance and reduce the capacity of veins to buffer changes in volume.
So, you can imagine how people at different points of this elastance curve might experience RIH differently. Some people who are at the higher end of that elastance curve due to prolonged spinal CSF leak – causing veins to overcompensate – or who might have a prior history of IIH, or who could have had dural adhesion scarring, might develop RIH more quickly or even right away with volume shifts from a procedure. While those people who are at the lower end of that elastance curve – so someone who’s just gotten a leak and then gets treated quite quickly or in people who have a really highly compliant dura – may not develop RIH or have really mild symptoms.
In some cases, RIH may only manifest when the treatment-related fibrosis. So when we patch someone, they’re developing fibrosis they’re actually increases that elastance. They might only get those symptoms when that fibrosis happens, and there’s a tipping point in the elastance reserve for people.
So, I hope you’ve been able to see how insights into RIH will help us better understand spinal CSF pathophysiology and how the body changes to compensate for leak. To that end, I advocate for a few things. I think we should add RIH to the ICHD-4 criteria – that’s the diagnostic manual that we have for headache. With that formal diagnostic code, we could do more research. I’m also advocating for multi-institutional studies assessing the development of RIH at standard time points. And I hope, again, in a few years, we’ll be talking about RIH quite differently. Thank you.