What is decerebrate posturing?

Decerebrate Posturing: Definition and Clinical Significance

Decerebrate posturing is an abnormal motor response characterized by rigid extension of all extremities with internal rotation and pronation, indicating severe brain injury at the midbrain level or massive bilateral forebrain damage. 1, 2

Clinical Characteristics

Decerebrate posturing manifests as:

• Exaggerated extensor posture of all extremities with rigid extension, internal rotation, and pronation 2
• Shortening and lengthening reactions that can be modified by tonic neck reflexes, labyrinthine reflexes (Magnus-de Kleijn), and phasic spinal reflexes 2
• Distinction from simple extensor posturing: True decerebrate rigidity requires the presence of these modifiable reflexes, not just extensor posture alone 2, 3

Anatomical Localization

The posturing typically indicates:

• Midbrain lesions are the most common anatomical substrate, with significant correlation between midbrain injury and decerebrate posturing 2, 4
• Massive bilateral forebrain lesions can produce identical posturing when accompanied by roving eye movements and preserved brainstem reflexes 5
• Pontine involvement appears to be of secondary importance in the pathophysiology 4

Clinical Grading Context

Decerebrate posturing represents severe neurological dysfunction across multiple grading scales:

• Hunt and Hess Grade 4: Stupor, hemiparesis, early decerebrate posturing 1
• Hunt and Hess Grade 5: Coma, decerebrate posturing, moribund appearance 1
• World Federation of Neurological Surgeons Grade 4-5: Glasgow Coma Scale 3-12 with or without motor deficit 1
• Grade IV encephalopathy: Comatose state with decerebrate posture indicating extreme risk of imminent death or irreversible brain damage 1, 6

Prognostic Implications

The presence of decerebrate posturing carries significant prognostic weight:

• Mortality rate of approximately 80% in head-injured patients exhibiting decerebrate rigidity 2
• Increased mortality from 20% to 70% when extensor posture is present compared to its absence 2
• Incidence of up to 40% in head-injured patients 2
• Recovery potential depends on etiology: Metabolic causes (potentially reversible) versus structural brainstem damage (poor prognosis) 6, 7

Critical Diagnostic Pitfalls

Several important caveats must be recognized:

• Do not equate with simple extensor posturing: "Tonic and cerebellar fits" are forms of muscle spasm from brainstem irritation, not true decerebrate rigidity 2
• Spinal cord automatisms can mimic decerebrate posturing after brain death, appearing in delayed fashion and potentially confounding diagnosis 8
• False positive rate of 15% (95% CI, 5%-31%) when using decerebrate posturing alone to predict poor neurologic outcome 6
• Cannot distinguish from decorticate posturing for prognostication purposes in post-cardiac arrest patients, as both have unacceptable false positive rates when used alone 6

Etiological Considerations

Common causes include:

• Trauma is the most common cause of decerebrate rigidity in humans 2, 3
• Hemorrhagic stroke with brainstem involvement 1
• Metabolic encephalopathy including hepatic encephalopathy and hyperammonemia 1, 7
• Sequential bihemispheric strokes producing massive bilateral forebrain injury 5