What is cerebral palsy and what causes it?

- [Voiceover] Cerebral palsy is actually an umbrella term that we use to describe a group of disorders that affect a person's ability to move in a normal way. And cerebral palsy occurs because of damage to the developing brain. May be caused by an infection, or loss of oxygen for some reason. And this damage, it usually occurs during early development, anywhere from in utero to about toddlerhood, so while the brain is still undergoing really critical development. This damage, it occurs in parts of the brain that control our movements, and this damage, it is permanent. But it's not progressive, so the initial damage to the brain, it doesn't worsen over time, but the problems with movement do persist for the affected person's entire life. Now that we know a little bit more about cerebral palsy we can make a bit more sense of the name. Cerebral means brain, so this is where the damage is. And palsy means muscle weakness, or loss of function. This is describing the main problem that arises from this damage in the brain. Let's highlight the general parts of the brain here that are involved in movement. These will typically be the areas that get damaged to cause cerebral palsy. We've got the cerebellum and the motor cortex. These are the two bits that we can see if we look at the brain from the outside. And then if we go a little bit deeper inside the core of the brain, we've got the basal ganglia. These three parts of our brain, we can think of them as our movement centers. And what they're involved in are things like helping us make movements. So they help us coordinate and move our arms, and our legs, and our torsos. But they also help us do things like maintain our balance and control our posture, our muscle tone, and our reflexes. So it kind of follows that when these movement centers themselves, or the tracks of neurons that they use to communicate with each other and with our muscles, when any of these components are damaged during development the person will develop problems with their movements. And that's what we call cerebral palsy. One of the interesting issues with cerebral palsy is that the amount of trouble that each person has with their movements can vary a lot between different people. So let's explore this a little bit further. Let's draw a severity spectrum here for cerebral palsy. The further to the right we go, the more trouble the person has with their movements. On the left here, on the mild end of our spectrum we'll have people who aren't too badly affected from a functional, day-to-day point of view. This little boy here, it looks like he's able to walk and run around pretty well. And we know that cerebral palsy can cause trouble with posture, and balance, and coordination. So because this boy is able to run around like this we would say that he's not too severely affected. His form of cerebral palsy is quite mild. He'll still have some movement problems; Maybe he can't run quite as fast as someone without cerebral palsy. Or maybe he has some trouble with coordination. So maybe something like running and throwing a ball at the same time. But overall he's able to function pretty well on a day-to-day basis. But if we head over here to the severe end of our spectrum, the picture looks quite different. This girl here also has cerebral palsy but instead of being able to run around, she needs to be in a wheelchair. And it looks like she's having trouble with her posture so she needs to be held upright. And, you know, her cerebral palsy, it is so severe that she can't really get around by herself in her chair. It looks like she needs someone to operate it for her. So let's actually relabel the ends of our spectrum here so that we're painting a better picture of how wide this range of movement problems really is in cerebral palsy. Let's say that the severity spectrum for cerebral palsy goes from running to wheelchair, and everything in between. So this gives us a pretty good idea of how wide that range of movement problems can be. So what we're actually looking at here is something called the gross motor function classification system, or the GMFCS. And each of these pictures here actually represents the different levels of the GMFCS. So this system is a really useful way for characterizing the severity of someone's cerebral palsy. It gives us a good, fairly standard way, to get an idea of a person's movement abilities or their movement impairments. So let's leave this for a moment and go back to those damaging events that I mentioned, the events that damage the movement centers during development and cause cerebral palsy. Let's make another spectrum here, and this time we'll make a spectrum of causes. And we'll make this spectrum a little different. Let's go from nature on this end to nurture on this end. Nature refers to things that we're born with, things that are innate, like our genes or our chromosomes. And by nurture we're referring to our environment after we're born, so all of our personal experiences. And actually different causes of cerebral palsy can happen at different periods of early development. Let's do some color coding as well. Anything that I write on the spectrum in blue, that's happening before birth, so prenatally. And anything that I write in green, that's gonna be happening during the birth process, so perinatally. And anything in this nice salmon color here can be for things that happen after birth, up to the first few years of life, so postnatally. Let's start with events that can occur before birth, so in utero. All the way over on the nature end of our spectrum we can put genetics. There are a few genetic causes of cerebral palsy. So mom or dad, maybe they inadvertently passed on a mutated gene that results in damage to one of these movement centers in the brain But these are pretty rare causes of cerebral palsy, so the rest of the prenatal events that can cause cerebral palsy fall in between nature and nurture. They happen before birth, they are prenatal causes, but they have a bit more to do with the environment that the fetus is in. So we'll put these prenatal events around here on our spectrum of causes. The first event that we'll pop down here is infections, infections that the fetus gets from mom, so congenital infections. And one group of congential infections that can cause cerebral palsy is a group referred to as the TORCH infections. TORCH is a mnemonic for toxoplasmosis, rubella, cytomegalovirus, and herpes simplex virus. And there are actually two types of herpes simplex virus, type one and two, so we'll put both of these down here. I left this one for last on purpose because it's kind of a catch all. The O stands for other, just kind of because we had to make the mnemonic fit somehow, but we can put other infections down here like syphilis in this group. Because even though they don't really start with any of these letters, they can still cause cerebral palsy. So other things that can go wrong in the prenatal period. Well, we can run into some problems with the placenta. If we check out our developing fetus here, here's the placenta and here's the umbilical cord. These two are what allow the fetus to get oxygen and nutrient-rich blood from mom. Sometimes, the placenta, it doesn't form properly or it can be damaged during gestation. And when this happens, the placenta can't really do its job of delivering oxygen and all of those important nutrients to the fetus, which the fetus really counts on to develop properly. We call this placental insufficiency, and this is another possible cause of cerebral palsy. And one other thing that we'll put down here in our prenatal period is prematurity. This is when a baby is born early, defined as before 37 weeks of development in utero. And just to put that in some context, a baby that's born on time-- and we call these babies "term babies"-- they're born around the 40 week mark. And one of the main reasons that we're putting down prematurity here on our causes spectrum is because the brains of premature babies can be really fragile, and susceptible to damage. And there's actually a particular kind of brain damage that premature babies are at risk for that can cause cerebral palsy. And this is called periventricular leukomalacia, or PVL for short. Periventricular means around the brain ventricles, which play a part in keeping our brain nourished. And leuko, which means white, refers to the white matter in the brain. PVL is a type of brain injury of the white matter of the brain that lives around the ventricles. And it turns out that the vast majority of babies with PVL end up developing cerebral palsy, because these periventricular areas, they contain some really important tracks of neurons that are involved in controlling our movements. So prematurity puts a baby at risk for developing PVL, and PVL often causes cerebral palsy. Maybe we'll put PVL here in brackets beside prematurity just so that we remember one of the main reasons that we're putting prematurity down here on our causes spectrum. So what about the perinatal period? What sort of events can occur during the birth process and cause cerebral palsy? Well, if mom has one of those TORCH infections, instead of the fetus getting it during pregnancy, mom might actually pass on one of these infections to her baby during the birth process, as the baby is coming out of the birth canal. So we can put TORCH infections down here again, this time as a perinatal cause of cerebral palsy. And you can see that we're trending down our spectrum a bit, progressively to the right towards the nurture end. And that's because we're kind of getting into the realm of nurture, we're moving more towards those environmental causes that happen after birth. The second perinatal event that we can put down here is oxygen deprivation, or birth asphyxia. This happens when something gets in the way of the baby's ability to breathe. So, for example, if the umbilical cord gets caught around the baby's neck while it's being delivered. We actually used to think that this lack of oxygen, because of complications of birth like problems with the umbilical cord was the cause of cerebral palsy. But now we know that this type of event only occurs for a handful of cases of cerebral palsy, less than about 10%. And that the majority of things that go wrong and cause cerebral palsy actually happen during the prenatal period. Now let's go on and look at events that can happen during the postnatal period. And remember, here we're referring to the period after birth, up until the first few years of age. And now we can jump all the way over here to the nurture end of our spectrum of causes. Here we've got things like head trauma, so maybe the baby's brain was damaged during a car accident, or maybe they had a near drowning experience and that deprived them of oxygen and this damaged the brain. Because remember that our brain tissues really rely on oxygen in order to stay nice and healthy. And on that note we can put down stroke as another cause. This is another event that reduces oxygen flow to the brain which can damage those developing movement centers. And it's really important to note that strokes don't just happen in elderly people; They can happen in infants too, and they can cause cerebral palsy. And let's make our last example infections, and the major cerebral palsy-causing infection we can see postnatally is actually not a TORCH infection, it's bacterial meningitis. This is when the meninges, the protective coverings that we have around our brain and our spinal cord, when these become infected. In meningitis you get this really large inflammatory reaction around these parts of the brain. There's essentially a war going on between our immune system and the meningitis-causing bacteria. And if you've ever seen any war movies or taken any history classes, just imagine what the battlefield looks like when the war is over, or even while it's still raging. It's pretty damaged. And unfortunately in meningitis, our brain is the battlefield, and can thus become quite damaged. So if this battle goes on around any of the movement areas then we can end up with cerebral palsy. And by the way, I should clarify that these damaging events, they can cause cerebral palsy, but they won't cause it every time that they happen. So in other words it's totally possible for someone to have one of these events occur and not develop cerebral palsy.