Abnormal posturing

Abnormal posturing is an involuntary flexion or extension of the arms and legs, indicating severe brain injury. It occurs when one set of muscles becomes incapacitated while the opposing set is not, and an external stimulus such as pain causes the working set of muscles to contract. The posturing may also occur without a stimulus. Since posturing is an important indicator of the amount of damage that has occurred to the brain, it is used by medical professionals to measure the severity of a coma with the Glasgow Coma Scale (for adults) and the Pediatric Glasgow Coma Scale (for infants).

Three types of abnormal posturing are decorticate posturing, with the arms flexed over the chest; decerebrate posturing, with the arms extended at the sides; and opisthotonos, in which the head and back are arched backward.

The presence of posturing indicates a severe medical emergency requiring immediate medical attention. Decerebrate and decorticate posturing are strongly associated with poor outcome in a variety of conditions. For example, near-drowning victims that display decerebrate or decorticate posturing have worse outcomes than those that do not. Changes in the condition of the patient may cause him or her to alternate between different types of posturing.

Causes
Posturing can be caused by conditions that lead to large increases in intracranial pressure. Such conditions include traumatic brain injury, stroke, intracranial hemorrhage, brain tumors, and encephalopathy. Posturing due to stroke usually only occurs on one side of the body and may also be referred to as spastic hemiplegia. Diseases such as Malaria are also known to cause the brain to swell and cause this posturing effect.

Decerebrate and decorticate posturing can indicate that brain herniation is occurring or is about to occur. Brain herniation is an extremely dangerous condition in which parts of the brain are pushed past hard structures within the skull. In herniation syndrome, which is indicative of brain herniation, decorticate posturing occurs, and, if the condition is left untreated, develops into decerebrate posturing.

Posturing has also been displayed by patients with Creutzfeldt-Jakob disease, diffuse cerebral hypoxia, and brain abscesses.

In children
In children younger than age two, posturing is not a reliable finding because their nervous systems are not yet developed. However, Reye's syndrome and traumatic brain injury can both cause decorticate posturing in children.

For reasons that are poorly understood, but which may be related to high intracranial pressure, children with malaria frequently exhibit decorticate, decerebrate, and opisthotonic posturing.

Decorticate posturing


Decorticate posturing is also called decorticate response, decorticate rigidity, or flexor posturing. Patients with decorticate posturing present with the arms flexed, or bent inward on the chest, the hands are clenched into fists, and the legs extended. A person displaying decorticate posturing in response to pain gets a score of three in the motor section of the Glasgow Coma Score.

There are two parts to decorticate posturing. The first is the disinhibition of the red nucleus with facilitation of the rubrospinal tract. The rubrospinal tract facilitates motor neurons in the cervical spinal cord subserving flexor muscles of the upper extremities. The second component of decorticate posturing is the disinhibition of the lateral vestibulospinal tract which facilitates motor neurons in the lower cord serving extensor muscles of the lower extremities. The disinhibition of these two tracts by lesions above the red nucleus is what leads to the characteristic flexion posturing of the upper extremities and extensor posturing of the lower extremities.

Decorticate posturing indicates that there may be damage to areas including the cerebral hemispheres, the internal capsule, and the thalamus. It may also indicate damage to the mesencephalic region, or the corticospinal tract, along which impulses travel from the brain to the spinal cord. While an ominous sign of severe brain damage, the damage of which decorticate posturing is indicative is not as serious as that indicated by decerebrate posturing.

Decerebrate posturing
Decerebrate posturing is also called decerebrate response, decerebrate rigidity, or extensor posturing. In decerebrate posturing, the head is arched back, the arms are extended by the sides, and the legs are extended. A hallmark of decerebrate posturing is extended elbows. A person displaying decerebrate posturing in response to pain gets a score of two in the motor section of the Glasgow Coma Score.

Decerebrate posturing indicates brain stem damage or rather damage below the level of the red nucleus (e.g. mid-collicular lesion). It is exhibited by people with lesions or compression in the midbrain and lesions in the cerebellum.

A patient with decorticate posturing may begin to show decerebrate posturing, or may go from one form of posturing to the other; progression from decorticate posturing to decerebrate posturing is often indicative of uncal (transtentorial) or tonsilar brain herniation. Posturing may occur on one or the other side of the body, or it may occur on both sides. Activation of gamma motor neurons is thought to be important in decerebrate rigidity due to studies in animals showing that dorsal root transection eliminates decerebrate rigidity symptoms.

History
Sherrington was first to describe decerebrate posturing after transecting the brain stems of cats and monkeys, causing them to exhibit the posturing.