Abnormal posturing

The presence of abnormal 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 patients who display decerebrate or decorticate posturing have worse outcomes than those who do not. Changes in the condition of the patient may cause alternation between different types of posturing.

Types

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 opisthotonus, in which the head and back are arched backward.

Decorticate

Decorticate posturing is also called decorticate response, decorticate rigidity, flexor posturing, or, colloquially, "mummy baby". 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 and feet turned inward. A person displaying decorticate posturing in response to pain gets a score of three in the motor section of the Glasgow Coma Scale, caused by the flexion of muscles due to the neuro-muscular response to the trauma.

There are two parts to decorticate posturing.

• The first is the disinhibition of the red nucleus with facilitation of the rubrospinal tract due to severment of the corticospinal tract. The rubrospinal tract facilitates motor neurons in the cervical spinal cord supplying the flexor muscles of the upper extremities. The rubrospinal tract and medullary reticulospinal tract biased flexion outweighs the medial and lateral vestibulospinal and pontine reticulospinal tract biased extension in the upper extremities.
• The second component of decorticate posturing is the disruption of the lateral corticospinal tract which facilitates motor neurons in the lower spinal cord supplying flexor muscles of the lower extremities. Since the corticospinal tract is interrupted, the pontine reticulospinal and the medial and lateral vestibulospinal biased extension tracts greatly overwhelm the medullary reticulospinal biased flexion tract.

The effects on these two tracts (corticospinal and rubrospinal) 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 midbrain. While decorticate posturing is still an ominous sign of severe brain damage, decerebrate posturing is usually indicative of more severe damage at the rubrospinal tract, and hence, the red nucleus is also involved, indicating a lesion lower in the brainstem.

Decerebrate

Decerebrate posturing is also called decerebrate response, decerebrate rigidity, or extensor posturing. It describes the involuntary extension of the upper extremities in response to external stimuli. 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. The arms and legs are extended and rotated internally. The patient is rigid, with the teeth clenched. The signs can be present on only one side of the body or on both sides, and they may be present just in the arms, and they may be intermittent.

A person displaying decerebrate posturing in response to pain receives a score of two in the motor section of the Glasgow Coma Scale (for adults) and the Pediatric Glasgow Coma Scale (for infants), due to the muscles extending because of the neuro-muscular response to the trauma.

Decerebrate posturing indicates brain stem damage, specifically 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. Decerebrate posturing is commonly seen in pontine strokes. 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. 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. Transection releases the centres below the site from higher inhibitory controls.

In competitive contact sports, posturing (typically of the forearms) can occur with an impact to the head and is termed the fencing response.