Coma with Decorticate Posturing
This patient is in a coma with decorticate posturing, likely secondary to a structural brain lesion causing mass effect and impending herniation from metastatic disease. The clinical presentation of flexed arm over chest with extended leg following deep painful stimuli, combined with a dilated unreactive pupil and impaired medial eye movement, indicates severe brainstem compression with transtentorial herniation.
Clinical Reasoning
Decorticate posturing is characterized by flexion of the upper extremities and extension of the lower extremities, which precisely matches this patient's presentation 1. This abnormal motor response indicates damage to the cerebral hemispheres or disruption of corticospinal pathways above the level of the red nucleus, typically from structural lesions causing increased intracranial pressure 2.
The additional findings strongly support this diagnosis:
- Dilated left pupil unresponsive to light indicates compression of the ipsilateral third cranial nerve, a classic sign of uncal herniation with brainstem compression 2
- Impaired medial eye movement on doll's eye maneuver suggests medial longitudinal fasciculus dysfunction from brainstem involvement 2
- Lack of response to deep painful stimuli confirms comatose state rather than postictal somnolence 2
Why Other Options Are Incorrect
This is NOT convulsive generalized status epilepticus because the patient is not actively seizing and demonstrates fixed abnormal posturing rather than rhythmic motor activity 2.
This is NOT decerebrate posturing, which would show extension of both upper and lower extremities, indicating more severe brainstem dysfunction at the level of the midbrain or below 2.
This is NOT focal motor seizure with postictal somnolence because the fixed abnormal posturing, dilated pupil, and absent brainstem reflexes indicate structural damage rather than transient postictal changes 2. Postictal deficits typically resolve over minutes to hours and would not present with fixed pupillary abnormalities.
This is NOT locked-in syndrome, which presents with preserved consciousness, vertical eye movements, and blinking, with quadriplegia due to ventral pontine lesions—none of which match this presentation 2.
Critical Management Implications
Given metastatic lung cancer as the primary diagnosis, brain metastases occur in approximately 50% of lung cancer cases and represent the most common intracranial tumors in adults 3, 4. The cerebral hemispheres are involved in nearly 80% of brain metastases 3.
The presence of unilateral pupillary dilation and decorticate posturing indicates extreme risk of imminent death or irreversible brain damage from herniation 2. This represents a true neurological emergency requiring:
- Immediate high-dose dexamethasone (16-100 mg/day in divided doses for acute neurologic deterioration) to reduce vasogenic edema 5
- Emergent neurosurgical consultation for potential surgical decompression, particularly given the signs of midline shift and herniation 5
- Brief hyperventilation (target PaCO2 to lower end of normal) may be considered temporarily until definitive measures are undertaken, given the extreme risk of death 2
- Urgent neuroimaging (MRI preferred) to define the extent of metastatic disease and mass effect 3
The prognosis for untreated cerebral metastases is poor, with median survival less than 2 months 3. However, the motor examination findings of decorticate or decerebrate posturing alone should not be used to predict poor neurologic outcome due to unacceptable false positive rates (10-15%) 2, though the combination with absent pupillary reflexes at 72+ hours post-insult has better predictive value 2.