Abnormal posturing classification

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Editor-In-Chief: C. Michael Gibson, M.S., M.D. [1]

Overview

The two types of abnormal posturing are decorticate and decerebrate posturing. Opisthotonos, in which the head and back are arched backward, is another form of abnormal posturing.

Decorticate Posturing

Decorticate posturing is also called decorticate response, decorticate rigidity, flexor posturing, or "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. Decorticate posturing indicates damage to the mesencephalic region, or the corticospinal tract, along which impulses travel from the brain to the spinal cord. 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 subserving 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. 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. Decerebrate posturing indicates brain stem damage or rather damage below the level of the red nucleus (eg. mid-collicular lesion). 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.[1]

References

  1. Berne and Levy principles of physiology/[editors] Metthew N. Levy, Bruce M. Koeppen, Bruce A. Stanton.-4th ed.Philadelphia, PA: Elsevier Mosby, 2006.

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