Abnormal posturing

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Abnormal posturing, which indicates severe brain injury, refers to an involuntary flexion or extension of the extremities (the arms and legs). 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.[1] 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).

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.

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.[2]

[edit] Causes

Posturing can be caused by conditions that lead to large increases in intracranial pressure.[3] Such conditions include traumatic brain injury, stroke, intracranial hemorrhage, brain tumors, and encephalopathy.[4] Decerebrate and decorticate posturing can indicate that brain herniation is occurring[5] or is about to occur.[3] 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.[5]

Posturing has also been displayed by patients with Creutzfeldt-Jakob disease.[6]

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.[7]

[edit] Decorticate Posturing

Decorticate posturing, with elbows, wrists and fingers flexed, and legs extended and rotated inward.
Decorticate posturing, with elbows, wrists and fingers flexed, and legs extended and rotated inward.

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.[1]

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.

[edit] Decerebrate Posturing

Decerebrate posturing is also called decerebrate response, decerebrate rigidity, or extensor posturing. In decerebrate posturing, the arms are extended by the sides, the head is arched back, and the legs are extended.[4] Decerebrate posturing indicates brain stem damage or rather damage below the level of the red nucleus. A patient with decorticate posturing may begin to show decerebrate posturing, or may go from one form of posturing to the other;[1] 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.[1]

[edit] References

  1. ^ a b c d AllRefer.com. 2003 “Decorticate Posture”. Retrieved January 15, 2007.
  2. ^ Nagel, FO; Kibel SM, Beatty DW. (1990). "Childhood near-drowning--factors associated with poor outcome". South African Medical Journal 78 (7): 422-425. PMID 2218768. Retrieved on 2007-01-23. 
  3. ^ a b Yamamoto, Loren G. 1996. “Intracranial Hypertension and Brain Herniation Syndromes: Radiology Cases in Pediatric Emergency Medicine". 5(6). Kapiolani Medical Center for Women and Children; University of Hawaii; John A. Burns School of Medicine. Retrieved January 24, 2007.
  4. ^ a b ADAM. 2005. "Decorticate Posture". Retrieved January 15, 2007.
  5. ^ a b Ayling, J (2002). "Managing head injuries". Emergency Medical Services 31 (8): 42. PMID 12224233. Retrieved on 2007-01-23. 
  6. ^ Obi, T; Takatsu M, Kitamoto T, Mizoguchi K, Nishimura Y (1996). "A case of Creutzfeldt-Jakob disease (CJD) started with monoparesis of the left arm". Rinsho Shinkeigaku (Clinical Neurology) 36 (11): 1245-1248. PMID 9046857. Retrieved on 2007-01-24. 
  7. ^ Idro, R; Otieno G, White S, Kahindi A, Fegan G, Ogutu B, Mithwani S, Maitland K, Neville BG, Newton CR. "Decorticate, decerebrate and opisthotonic posturing and seizures in Kenyan children with cerebral malaria". Malaria Journal 4 (57). PMID 16336645. Retrieved on 2007-01-21. 
  • Victor M, Ropper A. Adams and Victor's principles of neurology. 7th ed. New York: McGraw-Hill, 2001.
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