What is Decerebrate and Decorticate Posturing?
Decorticate and decerebrate posturing are both abnormal ways the body responds, usually due to harmful stimuli coming from either outside or inside the body. These responses mainly involve usual movements of the trunk and limbs and generally indicate severe brain or spinal damage. It’s interesting to note that Charles Sherrington, a Nobel laureate, first documented decerebrate posturing in 1898 upon studying the brains of live monkeys and cats.
Decorticate posturing is also called abnormal flexion, decorticate rigidity, flexor posturing, or decorticate response. Similarly, decerebrate posturing is known by other names like abnormal extension, decerebrate rigidity, extensor posturing, or decerebrate response.
However, some criticism has been raised in medical literature about using the terms decorticate and decerebrate posturing because they are associated with specific locations in the anatomy, which may not always be the case. Infections affecting different parts of the brain can cause both types of postures, but they typically involve some degree of brainstem damage. Still, it is widely agreed that decorticate posturing typically requires a more forward injury than decerebrate posturing. In most studies, this location is considered to be the red nucleus at a part of the midbrain called the intercollicular level.
What Causes Decerebrate and Decorticate Posturing?
Many things can lead to abnormal body posturing, such as different types of brain lesions, as well as more widespread issues like metabolic and infectious diseases.
Brain lesions can occur in two primary regions:
1. Supratentorial Lesions: These are found in the upper part of the brain and can be due to an abscess, bleeding outside the brain tissue (extra-axial hematoma), water on the brain (hydrocephalus), brain bleeding, increased pressure inside the skull, trauma to the brain, or a tumor.
2. Infratentorial Lesions: These are found in the lower part of the brain. Similar to supratentorial lesions, they can be due to an abscess, hydrocephalus, brainstem or diencephalic stroke, cerebellar or brainstem hemorrhage, traumatic brain injury, or a tumor.
3. Diffuse and Metabolic Factors: These can occur throughout the entire body or in the metabolism and include conditions such as cerebral malaria, irregular levels of certain chemicals in the body (like sodium, magnesium, and calcium), brain inflammation, liver-related brain disease, lack of oxygen leading to brain injury, low blood sugar, lead poisoning, brain or spinal cord infection, and Reye syndrome, a rare but severe condition that usually affects children and teenagers recovering from a viral infection.
In individuals who already have structural abnormalities in the nervous system, episodes of rigid and abnormal posturing can happen in response to many different factors. These factors include, but are not limited to, fever, low oxygen levels, metabolic disturbances, sensory irritation, low blood sugar, and irritation of the membranes covering the brain and spinal cord.
Risk Factors and Frequency for Decerebrate and Decorticate Posturing
Even though there’s no specific data on how often abnormal posturing happens, we do have information on the health issues that typically cause it. The main cause of abnormal posturing, including decorticate and decerebrate posturing, is traumatic brain injury (TBI). A 2019 study estimated that around 69 million people worldwide have a TBI each year. Of these, about 8% are severe. A severe TBI is when a patient’s Glasgow Coma Scale (a test used to measure a person’s level of consciousness) score is 8 or less.
Signs and Symptoms of Decerebrate and Decorticate Posturing
The Glasgow coma scale requires a trained observer to distinguish between normal and abnormal flexing of muscles, especially in the early stages of a brain injury. Different postures can indicate the state of the patient’s condition.
Decorticate posturing involves abnormal bending inwards of the arms, with the legs stretching out. This posturing can include slow bending of the elbow, wrist, and fingers while twisting inwards at the shoulder. The legs and feet would be stretched out, toes typically spread out and overextended.
Decerebrate posturing features pulling inwards and twisting of the shoulder, stretching at the elbows with turning of the forearm, and flexing of the fingers. Legs show the same signs as decorticate posturing – stretching out and inward twisting at the hip, with the extension of the knee and bending of the feet. Toes would be typically spread out and overextended. But, because ‘decerebrate’ is linked with a specific physiological meaning, sometimes it’s simply referred to as ‘extension.’
In the situation of brain herniation, a patient’s neurological status can worsen in stages. Starting from a stage in which the patient can follow commands, the patient might go through phase of reflexes and muscle tension, decorticate posturing. As more of the brain gets impacted, the patient may show signs of decerebrate posturing. In the final stages, when even more portions of the brain are involved, the patient may lose muscle resistance and become flaccid.
Testing for Decerebrate and Decorticate Posturing
Decorticate and decerebrate posturing are signs that indicate nerve injury, rather than conditions on their own. Multiple factors can cause these symptoms, so various tests may be needed to identify the root cause accurately. In situations where pressure from lesions is a concern, it may be beneficial to consider surgical treatments as soon as possible. For such cases, imaging tests like CT or MRI scans can be used for early detection.
Further investigations could involve laboratory tests for other potential causes such as infections and metabolic disruptions. These tests may include blood samples and spinal fluid examination.
Treatment Options for Decerebrate and Decorticate Posturing
The treatment for a brain injury focuses on addressing the root cause. This could involve making adjustments to improve bodily functions, or treating any infections that might be present. In cases of traumatic brain injury, removing blood that has collected outside of the brain (a condition known as extra-axial hematoma) can improve a patient’s chances of survival.
However, some conditions may not be reversible, such as brain damage caused by lack of oxygen (hypoxic brain injury). In these situations, doctors will offer supportive measures to ease symptoms and maintain quality of life as much as possible.
What else can Decerebrate and Decorticate Posturing be?
Both normal flexion, which is a reflex to pain, and decorticate posturing, an abnormal positioning of the body, can seem quite similar. However, normal flexion responds quickly and varies in its movement pattern, unlike the slow, recurring movements seen in abnormal flexion. In normal flexion, the shoulder moves away from the body, the wrist stays neutral or extends, and importantly, the legs do not extend. In contrast, abnormal flexion sees the shoulder moving towards the body with the wrist flexing, and a critical characteristic is leg extension.
Spinal reflexes can stay active even after brain death. In fact, one study reported that for 22% of the patients declared brain dead, motor spinal responses were still seen. These can often be mistaken as abnormal posturing movements named decerebration.
There are additionally other kinds of abnormal posturing like Opisthotonus and Paratonia, caused by various conditions including cerebral palsy, tetanus, brain injuries, and poisoning, which can resemble abnormal posturing. Opisthotonus is seen when the back and neck are extremely arched, whereas Paratonia typically occurs as a result of brain diseases or conditions causing brain degeneration.
Lastly, people with injuries to the corticospinal tract, like tissue death from inadequate blood supply (ischaemic strokes), bleeding, or tumors, can develop a condition known as spasticity, which causes muscle stiffness and involuntary spasms. This condition can result in the arms and legs being positioned in a way similar to decorticate posturing. However, in spasticity, the person remains conscious whereas in abnormal posturing, they do not.
What to expect with Decerebrate and Decorticate Posturing
Abnormal posturing, a certain body position that can occur after a brain injury, is often a distressing sign. Unfortunately, the survival rates are quite low, with only 37% of decorticate patients (those with certain injury to the brain cortex) surviving after a head injury, and an even lower 10% for decerebrate patients (those with specific damage to the brain).
Generally, children who are hospitalized due to a head injury have a mortality rate of 10% to 13%. However, in severe cases where the child exhibits decerebrate posturing, the mortality rate increases dramatically to 71%.
As for traumatic brain injury (TBI) with decerebrate posturing, previous studies have indicated mortality rates ranging from 68% to 83%. In such cases, chances for survival are much higher if the patient is younger, is admitted to the hospital within 6 hours of injury and if the injury caused an extradural hematoma, a type of blood clot outside of the brain. The odds of recovery decrease with acute subdural hematoma (a blood clot on the surface of the brain) and older age.
When it comes to patients who exhibit abnormal posturing after the brain has been deprived of oxygen, survival rates are not encouraging. A study reviewing 210 patients showed that abnormal posturing, or a GCS motor score of less than 4, one day after the injury, suggested almost no chance of regaining independence.
Similarly, patients with gunshot wounds to the head who demonstrate either decorticate or decerebrate posturing have almost no chance of a good recovery. The Hunt and Hess subarachnoid hemorrhage severity grading scale, which is used to assess the severity of bleeding around the brain, includes decerebrate posturing in its highest categories, 4 and 5, which have mortality rates of 42% and 77%, respectively.
Possible Complications When Diagnosed with Decerebrate and Decorticate Posturing
Based on what we know about an individual’s prognosis, complications can range from death to significant issues with brain function. In the immediate aftermath, patients in a coma may also have difficulty keeping their airway open and regulating their heart and lung functions.
Complications include:
- Death
- Poor functional neurological outcome
- Airway management problems
- Difficulty regulating cardiorespiratory system
Preventing Decerebrate and Decorticate Posturing
Since the main reason behind abnormal posturing is traumatic brain injuries (TBI), it’s crucial to take steps for public safety. Efforts should be made to minimize events like road accidents and workplace mishaps which often lead to such injuries. This public health initiative can potentially reduce the occurrences of these conditions.
