The neurologic evaluation and management of a patient with coma or altered consciousness can be intimidating for the student, because such patients are usually critically ill and may require prompt intervention. The fundamental principles behind the evaluation of a neurologic problem, however, should not be discarded. On the contrary, an orderly and hypothesis-based approach may be even more important in a comatose patient than in others, given the need for timely diagnosis and the relative limitations of history and examination.

DEFINITION

Coma is defined as a state of unarousable unresponsiveness. Typically, the patient lies with eyes closed and does not open them even to vigorous stimulation, such as sternal rub, nasal tickle, or nailbed pressure. Alterations in consciousness short of coma are often described using terms such as drowsiness, lethargy, obtundation, and stupor, but these terms tend to be used imprecisely and it is generally best to describe simply how the patient responded to various degrees of stimulation. The Glasgow Coma Scale (GCS) assigns a numerical score to a patient’s level of responsiveness and is commonly used by neurosurgeons in cases of head trauma (see Table 17-1). Its utility lies in its ease of use by nurses and paramedics, its inter-rater reproducibility, and its prognostic value following head injury. Although the GCS describes a level of responsiveness, it does not assist in determining the cause of coma.

CLINICAL APPROACH

An algorithm for approaching patients with coma or altered consciousness is presented in Figure 3-1. The initial steps of stabilization and evaluation culminate in the neurologic exam, which is performed with two goals in mind: to assess brainstem function and to look for focal signs. The differential diagnosis and further investigations stem from this clinical assessment.

1.Remember the ABCs. In any patient with altered consciousness, the airway, breathing, and circulation (ABC) should be checked and maintained according to usual protocols, including intubation and mechanical ventilation if required.

2.Look for obvious clues to etiology. A brief history and general exam should be performed to search for obvious clues. A history of medical problems such as diabetes, hepatic failure, alcoholism, or a seizure disorder may be provided by the family, noted on a medical alert bracelet, or deduced from prescription labels. The circumstances in which the patient was found can offer clues to the onset or etiology of depressed consciousness. The general exam may yield telling signs, such as an odor on the breath, needle tracks on the skin, or a tongue laceration. It is important to check for meningeal signs in any unconscious patient because both bacterial meningitis and subarachnoid hemorrhage may lead to depressed consciousness.

FIGURE 3-1. The approach to coma and altered consciousness. [ABC: airway, breathing, and circulation.]

3.Try reversing common reversible etiologies. Most emergency departments make it standard practice to administer naloxone, thiamine, and dextrose to any patient with depressed consciousness and no obvious etiology. Note that thiamine should always be given before glucose because the latter can precipitate Wernicke encephalopathy if given alone.

4.Check brainstem reflexes and look for focal signs. These are the two primary goals of the neurologic exam in this setting, because the subsequent diagnostic and therapeutic steps will depend on these clinical findings.

5.Assess for all medication exposure. All comatose patients should have a toxicology screen for substances of abuse and other drugs. It is also important to remember what medications were administered in the emergency setting, including for intubation, as they can impact the findings of the neurologic exam. Remembering the half-life of the drug and mechanisms of action will help inform the interpretation of the exam.

Cranial nerves (CNs) should be examined in detail, because this is the portion of the exam most relevant to the assessment of brainstem function. In an arousable patient, most CNs can be tested in the usual manner. In a patient who is not arousable enough to follow commands, several important brainstem reflexes should be tested (Table 3-1), including the pupillary, corneal, oculocephalic, and gag reflexes. In addition, a funduscopic examination should always be performed. For many patients with altered consciousness, testing for a blink to visual threat may be the only way to judge visual fields. If the patient cannot move his or her face to command, the examiner may be restricted to looking for an asymmetry at rest, such as a flattened nasolabial fold on one side. Supraorbital pressure can be used to assess for facial asymmetries, as well as response to noxious stimuli. Bilateral nasal tickle also tests sensation in the trigeminal nerve (CN V)—which prompts a response via CN VII. This is less painful than supraorbital pressure. The presence of an endotracheal tube may make such testing difficult.

Motor tone should be checked in all extremities. If the patient can cooperate with some testing, a gross hemiparesis can be ruled out by having the patient hold the arms extended or legs elevated and observing for a downward drift. Otherwise, the examiner may be restricted to observing for asymmetry of spontaneous movements (or to asking caretakers whether all extremities have been seen to move symmetrically). Failing that, noxious stimuli such as nailbed pressure or a pinch on a flexor surface can be applied to each limb and the speed and strength of withdrawal noted, although abnormalities here may result from sensory loss as well as motor dysfunction. Decorticate and decerebrate posturing, signs of brainstem dysfunction, may be seen either spontaneously or in response to noxious stimuli (Fig. 3-2).

Muscle stretch reflexes can be tested in the usual manner, and a Babinski sign should be sought.

Sensory testing in most patients with altered consciousness is limited to testing of light touch or pain sensation. Noxious stimulation to each limb, as described previously, may be useful in looking for gross sensory abnormalities. In all cases in which noxious or invasive testing is needed, it is important to explain to the family and others at the bedside what the exam maneuvers and their purposes are before performing them, as noxious stimuli can be distressing for loved ones to watch.

Coordination may be tested in patients who are arousable enough.

FIGURE 3-2. Decorticate (above) and decerebrate (below) posturing. Both indicate brainstem dysfunction, although decorticate posturing suggests dysfunction slightly more superior than decerebrate posturing. (LifeART image Copyright © 2012 Lippincott Williams & Wilkins.)

DIFFERENTIAL DIAGNOSIS

In theory, there are two main ways in which consciousness can be depressed: the brainstem can be dysfunctional or both cerebral hemispheres can be dysfunctional simultaneously. As examples, acute disease in the brainstem (e.g., pontine hemorrhage) can lead to coma, as can processes affecting both cerebral hemispheres at once (e.g., hypoglycemia). Unilateral cerebral hemispheric lesions, however, can also lead to coma if they are large or severe enough to cause swelling and compression of the opposite hemisphere or downward pressure on the brainstem.

Accordingly, most neurologists interpret the information obtained from the exam of the comatose patient using the following principle: The presence or absence of brainstem reflexes suggests how deep the coma is, whereas the presence or absence of focal signs narrows the differential diagnosis and guides the workup.

Thus, in milder cases of depressed consciousness, the pupillary, corneal, and gag reflexes may all be preserved. In more severe cases, some or all of these brainstem reflexes may be lost, no matter what the etiology. (Note that if a brainstem reflex is abnormal in an asymmetric fashion, such as a unilateral unreactive pupil, this would be interpreted as a focal sign and suggests compression of, or primary disease in, the brainstem.)

BOX 3-1. Structural Causes of Depressed Consciousness

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The Sensory System Head Trauma Neurologic Investigations Neuro-Ophthalmology Demyelinating Diseases of the Central Nervous System Disorders of the Spinal Cord

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