Myths and Legends of Neuroscience: Recovery from TBI plateaus in two years

How long does it take before recovery ceases from a traumatic brain injury (TBI)?  When discussing recovery from TBI, it seems every basic neuroscientific principle is forgotten in favour of myths and legends.  Families are often told that recovery after TBI plateaus after two years.  In legal matters involving brain injury, neurosurgeons and neuropsychologists regularly trot out statements to the effect that “it is well known” or “it is generally accepted” that recovery after brain injury ceases after two years.   The “recovery takes two years” idea is inaccurate and represents a deep misunderstanding of what constitutes recovery from brain injury.  Here’s why…

Six Months to Recover

Once upon a time, in the days when doctors still made house calls, and coma was a marker of brain injury and not sedation, it was believed that recovery peaked six months after brain injury.  For decades there was a paucity of research on recovery after brain injury, in part because neuropsychology was in its infancy.  Much of what we knew came from research done on soldiers who had been injured during war.  By the 1980s substantial effort was being made into studying outcome after brain injury in civilian populations.  Research projects in those days tended to follow patients for six months, and 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, and so 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 outcome after TBI in those days.  Doctors were too embarrassed to admit that they knew nothing of what would happen after six months, so it was more comfortable (for the doctor) to tell patients that recovery plateaued at six months.

 

Recovery in Two Years

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 is usually so high.  You start off with hundreds of patients, but by two years you are left with only a handful.

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 Really Predicts Outcome?

It is curious that statements that are made about recovery after brain injury typically 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.

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.  (This is not to suggest that infants are immune to brain injury, or any other such nonsense.)  Why is this obvious fact not mentioned to patients?

In the last few years some very powerful studies have been mounted into understanding outcome after TBI, international studies involving 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; the bulk of recovery, 65%, remains unknown.  Clearly, we need to be cautious when making statements about outcome.  We need to consider the many predictors of outcome that have been identified and keep the limits of our knowledge in mind.

Isn’t it strange, then, that when doctors are asked how long it will take for a patient to recover from a brain injury, they do not respond by saying that it depends on the severity of the brain injury, the age of the patient, pathology visible on CT brain scans, the presence of hypotension, extent of extracranial injuries and other such factors, but instead trot out this mythical statement that it will take two years.  What happened to clinical reasoning?

The Nature of Recovery

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, but if it is still present by a year and there has been minimal change over the months, 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.

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.

Social competency may be drastically affected 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

It might be argued that some of the long-term gains discussed above 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, and that any improvements thereafter arise because the patient has learnt to adapt.  This view represents a rather peculiar take on the situation, and one that seems to suggest that psychological processes have no physiological correlate.  What, after all, is psychological adaptation if not a changed physiological process in the brain?

In this context, recovery is an improvement in a brain function that was impaired after TBI.  Recovery does not mean that the physical structure of the brain, “the wiring,” must return to the same configuration as before the injury.  It simply means that after TBI, a given brain function shows improvement for a while, and that after some time the initial gains come to an end.

 

Implications

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 fundamentally important characteristics of the injury, such as the duration of post-traumatic amnesia, the patient’s initial score on the Glasgow Coma Scale, the extent of radiologically proven brain injury, etc, we are still unable to accurately predict outcome, and cannot 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 and to stop preaching the “it takes two-years to recover” generalisation.