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Decerebrate posturing (decerebrate rigidity, abnormal extensor reflex) is characterized by adduction and extension of the arms, with the wrists pronated and the fingers flexed. The legs are stiffly extended, with plantar flexion of the feet. In severe cases, the back is acutely arched (opisthotonus). (See Recognising decerebrate posture.) This sign indicates upper brain stem damage, which may result from primary lesions, such as infarction, hemorrhage or tumor; metabolic encephalopathy; head injury; or brain stem compression associated with increased intracranial pressure (ICP). This postural pattern was first described by Sherrington, who produced it in cats and monkeys by transecting the brainstem at the intercollicular level.
If you observe decerebrate rigidity/posture:
Decerebrate rigidity may be elicited by noxious stimuli or may occur spontaneously. It may be unilateral or bilateral. With concurrent brain stem and cerebral damage, decerebrate rigidity may affect only the arms, with the legs remaining flaccid. Alternatively, decerebrate rigidity may affect one side of the body and decorticate rigidity the other. The two postures may also alternate as the patient’s neurologic status fluctuates. Generally, the duration of each posturing episode correlates with the severity of brain stem damage.
Decerebrate rigidity/posture results from damage to the upper brain stem. In this posture, the arms are adducted and extended, with the wrists pronated with the fingers flexed. The legs are stiffly extended, with plantar flexion of the feet.
Relief of high ICP by removal of spinal fluid during a lumbar puncture may precipitate cerebral compression of the brain stem and cause decerebrate posture and coma.
Inform the patient’s family that decerebrate posture is a reflex response, not a voluntary response to pain or a sign of recovery. Offer emotional support.