The 7 Phenotypes of Concussion: Part1
When it comes to concussion recovery, it's critical to recognize that not all concussions are the same. We now know that different phenotypes, or symptom profiles, manifest in response to concussions. Identifying these distinct phenotypes helps tailor the treatment process to the individual, improving the likelihood of effective recovery.
In this two-part series, we’ll explore the seven major concussion phenotypes. In Part 1, we’ll dive into three of the most common types: autonomic, vestibular, and visual/oculomotor phenotypes.
1. Autonomic Phenotype
Dysautonomia~ or dysfunction in the autonomic nervous system~ is one of the core components of the autonomic concussion phenotype. After a concussion, it's not uncommon for the autonomic system to be thrown way off balance. This system controls involuntary body functions like heart rate, digestion, blood pressure.... A hallmark sign of this dysfunction is increased symptoms in response to physical activity.
Patients often notice heightened symptoms like headaches, nausea, or dizziness when increasing their physical exertion. This is where tools like the Buffalo Concussion Treadmill Test (or Bike Test) come into play. These tests are designed to assess exercise intolerance~a common feature of the autonomic phenotype.
In addition to exercise intolerance, clinicians assess various factors like postural changes, pupil response, and isometric grip strength to evaluate autonomic function. One of the tools that can provide insight into the degree of autonomic involvement is the COMPASS 31, an outcome measure that breaks down all the components of the autonomic system. This tool can be an essential asset for therapists and physicians, giving them a broad view of how the autonomic nervous system might be contributing to a patient’s symptoms.
For clinicians, it’s important to acknowledge that autonomic dysfunction is one of the more challenging phenotypes to assess objectively. Often, it’s overlooked because many feel undertrained in this area. But there are objective measures that can help assess the autonomic nervous system’s functioning and guide treatment planning. The Buffalo Concussion Treadmill Test is one, but so are the COMPASS 31 and other assessments.
Recognizing autonomic involvement is vital because this phenotype doesn’t just impact exercise tolerance~it affects the entire nervous system. Symptoms of autonomic dysfunction often overlap with other phenotypes, and understanding this overlap can help clinicians tailor a more effective recovery plan.
2. Vestibular Phenotype
Next up! The vestibular system… the second phenotype we'll explore, and it’s one that many patients and clinicians are familiar with. The vestibular system plays a crucial role in balance, spatial orientation, and movement, and dysfunction in this system often results in dizziness, balance issues, and a general sense of disorientation.
When dealing with a vestibular phenotype, patients frequently report dizziness with movement~whether turning their heads, bending down, or walking. A common complaint is bumping into objects, typically on one side, or feeling like they’re veering off course while walking. Some describe a sensation of being disconnected from their bodies, feeling as though they’re floating or dissociated. This disorientation can often be mistaken for other conditions, making it crucial to assess vestibular function directly.
While dizziness is a common symptom, it is important to note that vestibular dysfunction doesn’t always manifest as dizziness. An example from my practice… patients with motion sickness or balance challenges may have vestibular issues that stem from an imbalance in their otoliths~the sensory structures in the inner ear responsible for linear acceleration. Asymmetry in the functioning of the otoliths may lead to persistent symptoms even when dizziness is not present.
Triggers for vestibular symptoms often include quick movements, elevators, escalators, or traveling in a car. These symptoms can arise from both central (brainstem-related) and peripheral (inner ear) sources, and they can be asymmetric, affecting one side of the body more than the other.
Clinicians assessing vestibular phenotypes should focus on specific components like the semicircular canals, which process angular acceleration, and the otoliths. It’s crucial to recognize that vestibular dysfunction may stem from various sources, whether peripheral damage, central processing issues, or a combination of both. Understanding the specific nature of the vestibular problem will inform treatment strategies, which may include vestibular rehabilitation therapy.
3. Visual/Oculomotor Phenotype
The visual or oculomotor phenotype is another key subtype that often presents after a concussion. Contrary to what many people think… visual clarity alone is not the sole indicator of visual system dysfunction. Instead, the oculomotor system~which controls eye movements~can become impaired after a concussion, leading to a wide range of symptoms.
Common symptoms of visual phenotype include dizziness, particularly when reading or scanning busy environments, bumping into objects, blurred or double vision, and headaches. Patients with this phenotype may find it difficult to focus their eyes, especially when moving between near and far objects, or when engaging with screens and reading. As with other phenotypes, dizziness can be a symptom of visual dysfunction, though it isn’t always present.
Triggers for visual symptoms include screen use, reading, and being in visually overwhelming environments like shopping centers. These tasks require the eyes to work together symmetrically, which becomes a challenge when the oculomotor system is impaired. For instance, poor binocular coordination~the ability of the eyes to work together~can cause blurred vision and difficulty focusing on objects.
This phenotype can be broken into two components: functional vision and visual processing. Functional vision refers to how well the eyes move and work together to take in the environment, such as when scanning a page or focusing on a target. Visual processing, on the other hand, relates to how the brain interprets the information received from the eyes. Both aspects can be affected by a concussion, and distinguishing between the two is important for targeted treatment.
Neuro-optometrists are specialists in this area, and they can assess binocular dysfunction and prescribe therapies to improve oculomotor coordination. Other clinicians, such as physical and occupational therapists, can also play a role in helping to retrain the visual system through specific exercises.
Common Themes in Phenotypes
As you can see… there is significant overlap between these phenotypes. Dizziness, for example, is a symptom shared by the autonomic, vestibular, and visual phenotypes, and balance challenges appear in more than one category. This overlap can make it difficult to immediately pinpoint a patient’s specific phenotype based on symptoms alone, underscoring the importance of objective assessment tools.
Outcome measures like the CP 29 Clinical Profile Screen Scale, which was developed to help categorize concussion phenotypes, are useful tools for guiding clinicians. This tool asks detailed questions to help identify the likely phenotype and where further investigation may be needed. While it covers five of the seven phenotypes, it’s a great starting point for clinicians looking to dig deeper into their patients' concussion profiles.
Moving Forward
These first three phenotypes ~autonomic, vestibular, and visual~ each require their own nuanced approach to treatment. If you find yourself relating to more than one of these categories, that’s not uncommon. Many patients experience persistent symptoms across multiple phenotypes, and recovery often involves addressing more than one aspect of the nervous system.
In Part 2, we will dive into the remaining four phenotypes of concussion, exploring how they manifest and how to approach their treatment. Stay tuned as we continue to break down the complexity of concussion recovery and offer actionable insights for clinicians and patients alike.
