I have now heard several stories of prisoners faking a coma. In one, he was intubated for a GCS of 8, and the first clue was that the television was mysteriously and seemingly autonomously rotated toward the patient. Eventually they lay a trap involving blocking access to the television, and were able to catch him in the act.
Patients do of course lie to us, but many patients have psychogenic coma, where they are not intentionally fabricating the coma, which arises from psychological distress and is termed a conversion reaction. How can physical diagnosis demonstrate to us that a patient is actually awake?
The oculocephalic (doll’s eye) responses can give either fixed eyes or reflex responses in these patients. However, the cold caloric oculovestibular reflexes are thought to be highly sensitive and specific, though they appear not to have been studied in this population. Irrigate an ear with 60-100mL of ice water. A patient in a true coma with an intact brainstem shows a slow tonic deviation of the eye toward the ice. Patients with damage to the brainstem show no response. A patient who is awake shows fast phase nystagmus away from the cold ear.
Plum and Posner write “it is the presence of normal nystagmus in response to caloric testing that firmly indicates that the patient is physiologically awake and that the unresponsive state cannot be caused by structural or metabolic disease of the nervous system.” Later on they do qualify this statement by suggesting that intense visual fixation might overcome this nystagmus in some situations.
Other findings that are not consistent with organic disease include resistance to eye opening and rapid/active eye closure once released. Coma findings that cannot be fabricated include the slow smooth closure of opened eyelids and roving eye movements.
Apparently the rolling upward of the eyeballs upon lid opening is a voluntary act, though I have not been able to find a citation for that. Dropping the arm on the face is commonly used, and usually helpful, though I have seen it give a misleading result. With a thorough history and examination, the hope is that the diagnosis will become more clear.
Take home points:
Fast nystagmus away from the ice indicates an awake patient
Resistance to eye opening and active eye closure suggests an awake patient
Plum and Posner The Diagnosis of Stupor and Coma. This is a classic text that is highly recommended.