What is Diffuse Axonal Injury?
Diffuse axonal injury (DAI) is a type of traumatic brain injury (TBI) that happens because of a solid blow to the head. Remarkably, TBI is one of the main reasons behind death and disability in children and young adults in the United States. According to the Center for Disease Control and Prevention (CDC), there are over 1.5 million reported incidents of TBI each year in the US.
The severity of TBI ranges from mild, moderate, to severe, which is determined by the Glasgow coma scale (GCS). Patients with a GCS of 13 to 15 have a mild TBI, a GCS of nine to 12 indicates a moderate TBI, and a GCS below eight suggests a severe TBI.
The GCS is a tool used to assess the patient’s ability to open their eyes, their verbal responses, and their motor responses. For example, a patient that opens their eyes spontaneously scores higher than one that doesn’t open them at all. Similar comparisons are made for verbal and motor responses.
In the case of DAI, it specifically impacts the white matter tracks in the brain. This can lead to various neurological problems which can range from being insignificant to resulting in a coma-like state. Unfortunately, most DAI cases are severe with a GCS of less than 8. Since a DAI is diagnosed based on the patient’s symptoms and evaluations, it is crucial to understand and identify the signs correctly.
What Causes Diffuse Axonal Injury?
Diffuse axonal injury typically happens because of high-speed car accidents. This kind of injury typically results from a rapid start-stop motion that puts strain on the brain’s white matter, or the parts of the brain that connect different areas and convey messages. This can cause both visible and microscopic damage to the nerve fibers in the brain, specifically where the brain’s gray and white matter meet. The areas most commonly affected are the corpus callosum and the brainstem, which play essential roles in connecting and communicating information between different parts of the brain. It’s also important to note that getting a diffuse axonal injury doesn’t necessarily mean there’s also a skull fracture.
Risk Factors and Frequency for Diffuse Axonal Injury
It’s hard to say exactly how often diffuse axonal injury (DAI) occurs. However, estimates suggest that about 10% of all patients admitted to the hospital with traumatic brain injury (TBI) might have some degree of DAI. Of those patients with DAI, about 25% are expected to pass away. This number might actually be lower than reality, as patients who have other types of brain injuries may not be correctly diagnosed with DAI. Studies performed after patients’ deaths have found that DAI often happens in cases of severe traumatic brain injury.
Signs and Symptoms of Diffuse Axonal Injury
Diffuse axonal injury (DAI) is determined clinically. It’s generally suspected in patients who score less than 8 on the Glasgow Coma Scale (a measure of consciousness) for over six hours. The symptoms of this condition depend on its severity. For instance, those with mild DAI may experience symptoms similar to a concussion, which include:
- Headache
- Dizziness
- Nausea
- Vomiting
- Fatigue
However, a severe diffuse axonal injury might cause the patient to lose consciousness and enter a vegetative state. Unfortunately, only a tiny percentage of these patients regain consciousness within the first year after the injury.
Another set of symptoms are related to dysautonomia, a disorder that affects automatic body functions. Common dysautonomic symptoms include:
- Rapid heart rate (tachycardia)
- Fast breathing rate (tachypnea)
- Sweating (diaphoresis)
- Low blood pressure (vasoplegia)
- High body temperature (hyperthermia)
- Abnormal muscle tone
- Abnormal body posturing
Testing for Diffuse Axonal Injury
Diffuse axonal injury is a severe type of brain injury that often takes place due to accidents. When a person gets a head injury, the usual course of action is to apply advanced trauma life support protocols.
Doctors can definitively diagnose a case of diffuse axonal injury by examining brain tissue after death. However, when the patient is still alive, the diagnosis is made based on symptoms and the results from brain scans. If a person has had serious head trauma that involves the head moving suddenly and violently, then diffuse axonal injury might be suspected. Specifically, if the patient scored less than 8 on the Glasgow Coma Scale (a system used to evaluate the severity of brain damage) for more than six hours straight following a head injury, a diagnosis of diffuse axonal injury could be considered.
Certain findings on a computed tomography (a type of brain scan), like small spots of bleeding in the brain’s white matter, might suggest diffuse axonal injury if the patient’s symptoms align with this condition. But overall, this type of scan doesn’t always clearly show injuries related to diffuse axonal injury.
Magnetic resonance imaging (MRI), especially a method known as diffuse tensor imaging, is currently the best way to help diagnose diffuse axonal injury. Recent studies suggest that a specific type of MRI called gradient-recalled echo might be even more effective at detecting this type of brain damage, particularly in more severe cases.
It’s important to note that if a person’s condition doesn’t improve after treatment for a subdural or epidural hematoma (types of bleeding around the brain), diffuse axonal injury should be seriously considered. On the contrary, if a person gets significantly better after treating these types of bleeding, they likely don’t have diffuse axonal injury.
Right now, there’s unfortunately no blood test that can diagnose diffuse axonal injury. However, research is ongoing to find molecular markers in the blood that could potentially help diagnose this condition in the future.
Treatment Options for Diffuse Axonal Injury
Treatment for patients suffering from widespread nerve damage (diffuse axonal injury) focuses on preventing additional harm and promoting recovery. Secondary injuries can often be more dangerous, leading to potentially fatal conditions such as low oxygen levels paired with low blood pressure, inflammation, and increased pressure inside the skull. So, it’s necessary to take quick measures to prevent these conditions.
When it comes to immediate treatment for traumatic brain injuries, the priority is resuscitation. In centers that don’t specialize in neurology, trauma surgeons and emergency doctors usually take charge of this initial revival and brain treatment. The goal is to stabilize the patient for quick transport to a specially equipped center for brain injuries.
If a patient’s rating on the Glasgow Coma Scale (a measure of consciousness) drops below 8, monitoring for pressure inside the skull is important. This is generally decided after consulting with neurosurgery experts. Monitoring could also be considered for patients who cannot undergo continuous neurological evaluations. This typically applies to patients being given general anesthesia, pain relief with opioids, sedation, and prolonged paralysis for treating other injuries. Along with monitoring pressure, it can also be helpful to track cerebral oxygen saturation, a measure of oxygen levels in the brain.
Typically, short-term treatment with anticonvulsant drugs can prevent early seizures following trauma. However, there’s no evidence to suggest that this can prevent long-term seizures after the trauma.
While there is emerging evidence suggesting that treatment with progesterone may reduce the severity of the disease and death rate in acute brain trauma patients, it’s not yet a widespread practice.
Overall, the aim in treating patients with widespread nerve damage is to provide supportive care while preventing any further injuries.
What else can Diffuse Axonal Injury be?
- Blood clot under the skull (Subdural Hematoma)
- Blood clot above the protective membrane of the brain (Epidural Hematoma)
- Bleeding into the space surrounding the brain (Subarachnoid Hemorrhage)
- Different kinds of bleeding in the brain (Intracerebral Hemorrhage)
- Strokes, caused by blood clots or bleeding in the brain
- A mild brain injury or symptoms that persist after a concussion (Concussion/Post-concussive Syndrome)
- Low blood sugar (Hypoglycemia)
What to expect with Diffuse Axonal Injury
The outlook tends to be less promising for patients with severe DAI.
Possible Complications When Diagnosed with Diffuse Axonal Injury
Dysautonomia, a condition that affects the nervous system, is quite common. However, there is yet to be a definite cure for this condition. As a result, patients are usually advised to manage the symptoms as best they can with supportive treatments.
Recovery from Diffuse Axonal Injury
If surgery is performed, the standard after-surgery care typically involves decreasing the intracranial pressure (pressure in the skull) and enhancing the blood flow to the brain.
Patients and their families should anticipate a long recovery process after severe DAI (diffuse axonal injury). This usually includes extensive physical therapy, occupational therapy, speech therapy, and other forms of mental health support.
