The patient is observed to assess respiration, limb position, and spontaneous movements. Myoclonus or seizures may be subtle (e.g., twitching of one or two fingers or the corner of the mouth). More florid movements, such as facial grimacing, jaw gyrations, tongue protrusion, or complex repetitive limb movements, may defy ready interpretation. Asymmetric movements or postures may signify either focal seizures or hemiparesis.

Assessment of motor tone is crucial in the examination of coma. Asymmetry of muscle tone suggests a structural lesion, but it is not always clear which side is abnormal. Gegenhalten, or paratonia, is variable resistance to passive movement that often increases with the velocity of the movement; it is attributed to diffuse forebrain dysfunction and is often accompanied by a grasp reflex. Rigidity is present throughout the entire range of movement, is often seen in combination with cogwheeling, and usually indicates basal ganglia dysfunction (e.g., parkinsonism) or symptomatic hydrocephalus. Spasticity has a characteristic “catch” midway through passive movement and indicates corticospinal pathway dysfunction. Acute transtentorial herniation often produces exaggerated lower extremity spasticity and clonus.

Motor responses to stimuli may be appropriate, inappropriate, or absent. Even when patients are not fully awake, they may be roused to follow simple commands. Some patients who respond only to noxious stimuli (e.g., pressure on the sternum or supraorbital bone; pinching the neck or limbs; or squeezing muscle, tendon, or nail beds) may make voluntary avoidance responses. The terms decorticate and decerebrate posturing are physiologic misnomers but refer to stereotyped hypertonic flexion or extension in response to noxious stimuli (Fig. 18.3). In decorticate rigidity, the arms are flexed, adducted, and internally rotated, and the legs are extended; in decerebrate rigidity, the arms and legs are all extended. These postures are most often associated with cerebral hemisphere disease, including hypoxic-ischemic or metabolic encephalopathy, but may follow upper brain stem lesions or
transtentorial herniation as well (see later section for a discussion of herniation syndromes). Flexor posturing generally implies a more rostral lesion and has a better prognosis than extensor posturing, but the pattern of response may vary with different stimuli, or there may be flexion of one arm and extension of the other. When these postures seem to occur spontaneously, there may be an unrecognized stimulus (e.g., airway obstruction or bladder distention). With continuing rostrocaudal deterioration, there may be extension of the arms and flexion of the legs until, with lower brain stem destruction, there is flaccid unresponsiveness. However, lack of motor response to any stimulus should always raise the possibility of limb paralysis caused by cervical trauma, Guillain-Barré neuropathy, or the locked-in state.

In Cheyne-Stokes respiration (CSR), periods of hyperventilation and apnea alternate in a crescendo-decrescendo fashion. The hyperpneic phase is usually longer than the apneic, so arterial gases tend to show respiratory alkalosis. CSR occurs with bilateral cerebral disease or metabolic encephalopathy. It usually signifies that the patient is not in imminent danger. Long-cycle CSR, with brief periods of apnea occurring every 1 to 2 minutes, is a stable breathing pattern and does not imply impending respiratory arrest. Conversely, “short-cycle CSR” (cluster breathing) with less smooth waxing and waning is often an ominous sign of a posterior fossa lesion or dangerously elevated ICP.

Sustained hyperventilation is usually due to metabolic acidosis, pulmonary congestion, hepatic encephalopathy, or during acute herniation (see Fig. 18.3). Rarely, it is the result of a lesion in the rostral brain stem. Apneustic breathing, consisting of long inspiratory pauses, is seen with pontine lesions, especially infarction; it occurs infrequently with metabolic coma or transtentorial herniation.

Respiration having a variably irregular rate and amplitude (ataxic breathing) indicates medullary damage and may progress to apnea, which also occurs abruptly in acute posterior fossa lesions. Loss of automatic respiration with preserved voluntary breathing (Ondine curse) occurs with medullary lesions; as the patient becomes less alert, apnea may be fatal. Other ominous respiratory signs are end-expiratory pushing (e.g., coughing) and “fish-mouthing” (i.e., lower jaw depression with inspiration). Stertorous breathing (i.e., inspiratory noise) is a sign of airway obstruction.

Pupillary abnormalities in coma may reflect an imbalance between input from the parasympathetic and sympathetic nervous systems or lesions of both. Although many people have slight pupillary inequality, anisocoria should be considered pathologic in a comatose patient. Retinal or optic nerve damage does not cause anisocoria, even though there is an afferent pupillary defect. Parasympathetic lesions (e.g., oculomotor nerve compression in uncal herniation or after rupture of an internal carotid artery aneurysm) cause pupillary enlargement and, ultimately, full dilation with loss of reactivity to light. Sympathetic lesions, either intraparenchymal (e.g., hypothalamic injury or lateral medullary infarction) or extraparenchymal (e.g., invasion of the superior cervical ganglion by lung cancer), cause Horner syndrome with miosis. With involvement of both systems (e.g., midbrain destruction), one or both pupils are in mid position and are unreactive. Small but reactive pupils following pontine hemorrhage are the result of damage to descending intra-axial sympathetic pathways.

With few exceptions, metabolic disease does not cause unequal or unreactive pupils. Fixed, dilated pupils after diffuse anoxia -ischemia denote a bad prognosis. Anticholinergic drugs, including glutethimide, amitriptyline, and antiparkinsonian agents, abolish pupillary reactivity. Hypothermia and severe barbiturate intoxication may cause not only fixed pupils but also a reversible picture that mimics brain death. Bilateral or unilateral pupillary dilation and nonreactivity may accompany (or briefly follow) a seizure. In opiate overdose, miosis may be so severe that a very bright light and a magnifying glass are necessary to detect reactivity. Some pupillary abnormalities are local in origin (e.g., trauma or synechiae).

Spontaneous blinking may occur with or without purposeful limb movements. Eyes that are conjugately deviated away from hemiparetic limbs indicate a destructive cerebral lesion on the side toward which the eyes are directed. Eyes turned toward paretic limbs may indicate a pontine lesion, an adversive seizure, or the wrong-way gaze paresis of thalamic hemorrhage. Eyes that are dysconjugate while at rest may indicate paresis of individual muscles, internuclear ophthalmoplegia, or preexisting tropia or phoria.

When the brain stem is intact, the eyes may rove irregularly from side to side with a slow, smooth velocity; jerky movements suggest saccades and relative wakefulness. Repetitive smooth excursions of the eyes first to one side and then to the other, with 2- to 3-second pauses in each direction (periodic alternating or
ping-pong gaze), may follow bilateral cerebral infarction or cerebellar hemorrhage with an intact brain stem.

If cervical injury has been ruled out, oculocephalic testing (the doll’s eyes maneuver) is performed by passively turning the head from side to side; with an intact reflex arc (vestibular system → brain stem → eye muscles), the eyes move conjugately in the opposite direction (Fig. 18.4). A more vigorous stimulus is produced by irrigating each ear with 30 to 60 mL of ice water. A normal, awake person with head elevated at 30 degrees has nystagmus with the fast component in the direction opposite the ear stimulated, but a comatose patient with an intact reflex arc has deviation of the eyes toward the stimulus, usually for several minutes. Simultaneous bilateral irrigation causes vertical deviation, upward after warm water and downward after cold water.