One of the myths in the neurosciences is that recovery after TBI (traumatic brain injury) plateaus two years after the injury. When discussing recovery from TBI, myths and legends abound. We tend to lose sight of basic neuroscientific principles. Clinicians tell families that recovery after TBI stops after two years. In legal matters, opinion can be even more dogmatic. We hear from esteemed experts that “it is well known” that recovery from brain injury plateaus after two years. Yet the “recovery takes two years” idea is inaccurate and represents a deep misunderstanding of what constitutes recovery after TBI. Here’s why…
Recovery after TBI: The Six Month Myth
For decades there was a paucity of research on recovery after brain injury. In part, this was because neuropsychology was in its infancy. Back then, research done on soldiers injured during wartime formed that backbone of our knowledge.
In the 1980s, researchers made an effort to study outcome after brain injury in civilian populations. Research projects in those days tended to follow patients for only six months. Consequently, we knew nothing about what happened after six months. As a result, doctors started to tell their patients that they had six months in which to recover. Thus, the elemental myth about recovery after TBI was born.
The six-month figure did not actually have anything to do with the duration of recovery, but simply reflected the typical duration of research into recovery after TBI in those days. It must have been difficult for doctors to admit that they knew nothing of what would happen after six months. Perhaps it was more comfortable (for the doctor) to tell patients that recovery plateaued at six months.
Recovery after TBI: The Two Year Legend
During the 1990s outcome studies started to track patients for longer periods, first a year, and then studies that followed patients for two years emerged. In fact, it is extremely difficult to mount a two-year follow-up study because the attrition rate in the cohort of patients is usually so high. Researchers start with a large sample of patients, but by two years only a handful remain.
Precisely because of the difficulties with casting the net further than two years, outcome studies lasting for two years became the new de facto standard. Hence, the recovery duration myth morphed from six months to two years and this is what we now tell our patients. The idea that recovery after brain injury plateaus at two years has become so ingrained that no-one thinks about it any more. It has assumed the status of a neuroscientific “law.”
What We Don’t Know
In the last few years, we have seen some very powerful studies into understanding outcome after TBI. These are international studies involving tens of thousands of patients. This research has advanced the field by a significant degree. Nonetheless, one of the fundamental messages to emerge is how little we know.
Our best scientific effort has enabled us to predict 35% of outcome. In other words, the majority of factors driving outcome, 65%, remain unknown. This enormous gap makes it clear that we need to be cautious when making statements about outcome. While we know of multiple predictors of outcome, we need to keep the limits of our knowledge in mind.
What Really Predicts Outcome?
Curiously, statements made about recovery after brain injury often ignore clinically obvious information. For example, we know perfectly well that severity of brain injury is a major determinant of outcome, and we know that the more severe the injury, the longer it takes to recover. Despite that knowledge, it is common for doctors to omit the crucial role of severity of brain injury and simple tell patients that it will take two years to recover. Surely it is obvious that a severe injury will take longer to recover than a mild injury?
We also know that the age of the patient is a major determinant of outcome; the older the patient, the worse the outcome and the longer it will take for recovery to reach a plateau. Strangely, we omit this obvious fact when discussing recovery after TBI with our patients.
In addition to the severity of the brain injury and the age of the patient, multiple other factors determine outcome. These include the amount of damage visible on brain scans, breathing difficulties, the presence of hypotension (low blood pressure), blood sugar abnormalities, and the like. Even extracranial injuries involving the body influence recovery after TBI. For instance, liver damage compromises the ability to recover from brain injury. Interestingly, the quality of the support received by the patient from family and friends is a major determinant of outcome.
Isn’t it strange, then, that doctors omit mention of the multiple determinants of outcome when asked how long it will take for a patient to recover after TBI? Instead, they often fob one off with the mythical statement that it will take two years. What happened to clinical reasoning?
The Nature of Recovery after TBI
If we think intelligently about recovery after brain injury, and apply some of the obvious facts that we know about the brain, then one of the first realisations is that recovery is not a unitary phenomenon and that it depends on the kind of brain function under consideration. We should expect a gradient of functional recovery, such that simpler brain functions recover more rapidly than complex brain functions.
For all their complexity, we know that sensory functions are simpler than motor functions, and this is borne out by research and clinical experience. For example, diplopia (double vision) may be present in the immediate aftermath of a concussion, but will typically rapidly abate. On the other hand, damage to the optic nerve is serious and if vision is not restored within the first four months, it is unlikely to return.
Hemiparesis due to injury to motor tracts may take more than six months to abate. If it is still present by a year and there has been minimal change, then it is unlikely to resolve and we should say that recovery from the hemiparesis has ceased. Notice that these are examples of recovery plateauing before the mythical two-year mark.
Complex Brain Functions
Emotional well-being, social behaviour and cognition are complex brain functions. Recovery of these brain functions is highly variable and may take years to improve and plateau. Cognitive functioning may take many years to improve, especially after severe brain injuries. Emotionally, patients may become depressed in the immediate aftermath, but then become happier and more positive as sensory and motor functioning normalises. However, when they start to encounter cognitive deficits that undermine their real-world functioning, depression may return. Thus, rather than improving in the long-term, emotional well-being may worsen.
Brain injury can drastically affect social competency initially. With the passage of time, therapy and feedback from the world, social skills gradually improve. Even beyond the mythical two-year mark, there may be substantial improvements in social interactions.
Compensation vs Recovery
There is a view that long-term gains represent psychological adaptations and compensation for specific deficits, rather than real physiological improvements in the brain. Proponents of the two-year recovery argument suggest that physiological recovery after TBI ceases at two years. On that view, adaptation accounts for any improvement thereafter. This view represents a rather peculiar take on the situation, and one that seems to suggest that psychological or physical adaptative processes have no physiological correlate. What, after all, is psychological adaptation if not a changed physiological process in the brain?
Recovery does not mean that the physical structure of the brain, “the wiring,” must return to the same configuration as before the injury. Recovery just means restoration of functioning.
Implications for Recovery after TBI
Current research tells us that we do not adequately understand predictors of recovery after TBI. We cannot say with certainty how long it will take to recover from a brain injury. Even if we know important characteristics of the injury, such as the initial score on the Glasgow Coma Scale, we are still unable to accurately predict outcome. We cannot confidently say when recovery will plateau. We might have learnt a massive amount about TBI in the last few years, but we still have a very long way to go.
It does a disservice to patients to tell them that there is no hope for improvement beyond the two-year mark. It is also unhelpful to dangle the carrot of hope when it should be clear that a given brain function is not going to recover any further. At this stage of the development of our knowledge, it is time to start thinking about prognosis and outcome relative to the specific patient. We need to stop preaching the “it takes two-years to recover” myth.