neurologic disorders
Overview of Coma and Impaired Consciousness
Diagnosis
History General physical examination Neurologic examination, including eye examination Laboratory tests (eg, pulse oximetry, bedside glucose measurement, blood and urine tests) Immediate neuroimaging Sometimes measurement of ICP If diagnosis is unclear, lumbar puncture or electroencephalography (EEG) Impaired consciousness is diagnosed if repeated stimuli arouse patients only briefly or not at all. If stimulation triggers primitive reflex movements (eg, decerebrate or decorticate posturing), impaired consciousness may be deepening into coma. Diagnosis and initial stabilization (airway, breathing, and circulation) should occur simultaneously. Temperature is measured to check for hypothermia or hyperthermia; if either is present, treatment is started immediately. Glucose levels must be measured at bedside to identify low levels, which should also be corrected immediately. If trauma is involved, the neck is immobilized until clinical history, physical examination, or imaging tests exclude an unstable injury and damage to the cervical spine. Medical identification bracelets or the contents of a wallet or purse (eg, hospital identification card, drugs) may provide clues to the cause. Relatives, paramedics, police officers, and any witnesses should be questioned about the circumstances and environment in which the patient was found; containers that may have held food, alcohol, drugs, or poisons should be examined and saved for identification (eg, drug identification aided by a poison center) and possible chemical analysis. Relatives should be asked about the following: The onset and time course of the problem (eg, whether seizure, headache, vomiting, head trauma, or drug ingestion was observed; how quickly symptoms appeared; whether the course has been progressive or waxing and waning) Baseline mental status Recent infections and possible exposure to infections Recent travel Ingestions of unusual meals Psychiatric problems and symptoms Prescription drug history Use of alcohol and other recreational drugs (eg, anesthetics, stimulants, depressants) Previous and concurrent systemic illnesses, including new-onset heart failure, arrhythmias, respiratory disorders, infections, and metabolic, liver, or kidney disorders The last time the patient was normal Any hunches they may have about what might be the cause (eg, possible occult overdose, possible occult head trauma due to recent intoxication) Medical records should be reviewed if available. Physical examination should be focused and efficient and should include thorough examination of the head and face, skin, and extremities. Examination of the heart and lungs is important to assess blood flow and oxygenation to the brain. Signs of head trauma include periorbital ecchymosis (raccoon eyes), ecchymosis behind the ear (Battle sign), hemotympanum, instability of the maxilla, and cerebrospinal fluid (CSF) rhinorrhea and otorrhea. Scalp contusions and small bullet holes can be missed unless the head is carefully inspected. If unstable injury and cervical spine damage have been excluded, passive neck flexion is done; stiffness suggests subarachnoid hemorrhage or meningitis. Findings may suggest a cause: Hypothermia: Environmental exposure, near-drowning, sedative overdose, severe hypothyroidism, Wernicke Encephalopathy , or, in older people, sepsis Hyperthermia: Heatstroke, infection, stimulant drug overdose, or neuroleptic malignant syndrome Fever, petechial or purpuric rash, hypotension, or severe extremity infections (eg, gangrene of one or more toes): Sepsis or central nervous system (CNS) infection Needle marks: Drug overdose (eg, of opioids orinsulin) A bitten tongue: Seizure Breath odor: Alcohol, other drug intoxication, or diabetic ketoacidosis Hypotension or pulse abnormalities: Cardiac dysfunction with hypoperfusion Difficulty breathing: Acute respiratory dysfunction from bacterial or viral illness The Introduction to the Neurologic Examination determines whether the brain stem is intact and where the lesion is located within the CNS. The examination focuses on the following: Level of consciousness Eyes Motor function Deep tendon reflexes Level of consciousness is evaluated by attempting to wake patients first with verbal commands, then with nonnoxious stimuli, and finally with noxious stimuli (eg, pressure to the supraorbital ridge, nail bed, or sternum). The Glasgow Coma Scale (see table Glasgow Coma Scale* ) was developed to assess patients with head trauma. For head trauma, the score assigned by the scale is valuable prognostically. For coma or impaired consciousness of any cause, the scale is used because it is a relatively reliable, objective measure of the severity of unresponsiveness and can be used serially for monitoring. The scale assigns points based on responses to stimuli. Eye opening, facial grimacing, and purposeful withdrawal of limbs from a noxious stimulus indicate that consciousness is not greatly impaired. Asymmetric motor responses to pain or deep tendon reflexes may indicate a focal hemispheric lesion. As impaired consciousness deepens into coma, noxious stimuli may trigger stereotypic reflex posturing. Decorticate posturingcan occur in structural or metabolic disorders and indicates hemispheric damage with preservation of motor centers in the upper portion of the brain stem (eg, rubrospinal tract). Decerebrate posturingindicates that the upper brain stem motor centers, which facilitate flexion, have been structurally damaged and that only the lower brain stem centers (eg, vestibulospinal tract, reticulospinal tract), which facilitate extension, are responding to sensory stimuli. Decerebrate posturing may also occur, although less often, in diffuse disorders such as anoxic encephalopathy. Flaccidity without movement indicates that the lower brain stem is not affecting movement, regardless of whether the spinal cord is damaged. It is the worst possible motor response. Asterixis and multifocal myoclonus suggest metabolic disorders such as uremia, hepatic encephalopathy, hypoxic encephalopathy, and drug toxicity. Psychogenic unresponsiveness can be differentiated from physiologically impaired consciousness by finding that although voluntary motor response is typically absent, muscle tone and deep tendon reflexes remain normal, and all brain stem reflexes are preserved. Vital signs are usually not affected. The following are evaluated: Pupillary responses Extraocular movements Fundi Other neuro-ophthalmic reflexes provide information about brain stem function (see table Interpretation of Pupillary Response and Eye Movements ). One or both pupils usually become fixed early in coma due to structural lesions, but pupillary responses are often preserved until very late when coma is due to diffuse metabolic disorders (called toxic-metabolic encephalopathy), although responses may be sluggish. If one pupil is dilated, other causes of should be examined. Papilledema may indicate increased ICP but may take many hours to appear; papilledema is usually bilateral. Increased ICP can cause earlier changes in the fundi, such as loss of retinal venous pulsations, disk hypermia, dilated capillaries, blurring of the medial disk margins, and sometimes hemorrhages. Subhyaloid hemorrhage may indicate subarachnoid hemorrhage. Theoculocephalic reflexis tested by the doll’s-eye maneuver in unresponsive patients: The eyes are observed while the head is passively rotated from side to side or flexed and extended.This maneuver should not be attempted if cervical spine instability is suspected. If the reflex is present, the maneuver causes the eyes to move in the opposite direction of head rotation, flexion, or extension, indicating that the oculovestibular pathways in the brain stem are intact. Thus, in a supine patient, the eyes continue to look straight up when the head is turned side to side. If the reflex is absent, the eyes do not move and thus point in whatever direction the head is turned, indicating the oculovestibular pathways are disrupted. The reflex is also absent in most patients with psychogenic unresponsiveness because visual fixation is conscious. If the patient is unconscious and the oculocephalic reflex is absent or the neck is immobilized, oculovestibular (cold caloric) testing is done. After integrity of the tympanic membrane is confirmed, the patient’s head is elevated 30°, and with a syringe connected to a flexible catheter, the examiner irrigates the external auditory canal with 50 mL of ice water over a 30-second period. If both eyes deviate toward the irrigated ear, the brain stem reflex is functioning normally, suggesting mildly impaired consciousness. If nystagmus away from the irrigated ear also occurs, the patient is conscious and psychogenic unresponsiveness is likely. In conscious patients, 1 mL of ice water is often enough to induce ocular deviation and nystagmus. Thus, if psychogenic unresponsiveness is suspected, a small amount of water should be used (or caloric testing should not be done) because cold caloric testing can induce severe vertigo, nausea, and vomiting in conscious patients. If the eyes do not move or movement is dysconjugate after irrigation, the integrity of the brain stem is uncertain and the coma is deeper. Prognosis may be less favorable. If muscle tone, deep tendon reflexes, and the response to the doll's-eye maneuver are normal, suspect psychogenic unresponsiveness. Certain patterns of eye abnormalities and other findings may suggest Brain Herniation (see also figure The spontaneous respiratory rate and pattern should be documented unless emergency airway intervention is required. It may suggest a cause. Inspection (Cheyne-Stokes or Biot respiration) may indicate dysfunction of both hemispheres or of the diencephalon. Hyperventilation (central neurogenic hyperventilation) with respiratory rates of > 25 breaths/minute may indicate midbrain or upper pontine dysfunction. An inspiratory gasp with respiratory pauses of about 3 seconds after full inspiration (apneustic breathing) typically indicates pontine or medullary lesions; this type of breathing often progresses to respiratory arrest. Initially, pulse oximetry, fingerstick plasma glucose measurements, and cardiac monitoring are done. Blood tests should include a comprehensive metabolic panel (including at least serum electrolytes, bloodureanitrogen [BUN], creatinine, and calcium levels), complete blood count (CBC) with differential and platelets, liver tests, and ammonia level. Arterial blood gases (ABGs) are measured, and if carbon monoxide toxicity is suspected, carboxyhemoglobin level is measured. Blood and urine should be obtained for culture and routine toxicology screening; serumethanollevel is also measured. Other toxicology screening panels and additional toxicology tests (eg, serum drug levels) are done based on clinical suspicion. ECG (12-lead) is also done to check for myocardial infarction and new arrhythmias. Chest x-ray should be done to check for new lung disease that may affect brain oxygenation. If the cause is not immediately apparent, noncontrast head CT should be done as soon as possible to check for masses, hemorrhage, edema, evidence of bone trauma, and hydrocephalus. Initially, noncontrast CT rather than contrast CT is preferred to rule out brain hemorrhage; CT detects cerebral bleeding and bone injuries (eg, skull fractures) best within 72 hours of injury. MRI can be done instead if immediately available, but it is not as quick as newer-generation CT scanners and may not be as sensitive for traumatic bone injuries ; however, MRI is now as sensitive as CT for detecting blood early as well as late. If noncontrast CT is not diagnostic, MRI or contrast CT can then be done; either of them may detect isodense subdural hematomas, multiple metastases, sagittal sinus thrombosis, herpes encephalitis, or other causes missed by noncontrast CT. MRI provides greater detail than CT when done > 72 hours after symptom onset but is more difficult logistically than CT if the patient is intubated. Classic lentiform (lens)-shaped hyperdensity that does not extend across suture lines. © 2017 Elliot K. Fishman, MD. Classic lentiform (lens)-shaped hyperdensity that does not extend across suture lines. © 2017 Elliot K. Fishman, MD. Classic crescent-shaped hyperdensity extending across suture lines. © 2017 Elliot K. Fishman, MD. Subfalcine herniation is the most common type of cerebral herniation. In this image, the left brain has herniated under the free edge of the falx cerebri (arrow) because hemorrhage from an infarct in the middle cerebral artery has increased intracerebral pressure. © 2017 Elliot K. Fishman, MD. If coma is unexplained after MRI or CT and other tests, Lumbar Puncture (Spinal Tap) (spinal tap) is done to check opening pressure and to exclude infection, subarachnoid hemorrhage, and other abnormalities. However, MRI or CT images should first be reviewed for intracranial masses, obstructive hydrocephalus, and other abnormalities that could obstruct CSF flow or the ventricular system and thus significantly increase ICP. Such abnormalities contraindicate lumbar puncture. Suddenly lowering CSF pressure, as can occur during lumbar puncture, in patients with increased ICP could trigger CSF analysis includes cell and differential counts, protein, glucose, Gram staining, cultures, and sometimes, based on clinical suspicion, specific tests (eg, cryptococcal antigen test, cytology, measurement of tumor markers, Venereal Disease Research Laboratory [VDRL] tests, polymerase chain reaction [PCR] for herpes simplex, visual or spectrophotometric analysis for xanthochromia). If increased ICP is suspected, CSF pressure is measured. If ICP is increased, Intracranial Pressure (ICP) Monitoring is done continuously, and If seizures may be the cause of coma, particularly if nonconvulsive status epilepticus (recurrent seizures without prominent motor symptoms) is being considered, or if the diagnosis remains uncertain, EEG may be done. In most comatose patients, EEG shows slowing and reductions in wave amplitude that are nonspecific but often occur in toxic-metabolic encephalopathy. In some patients with nonconvulsive status epilepticus, the EEG shows spikes, sharp waves, or spike and slow complexes. If psychogenic unresponsiveness or seizure activity (pseudoseizure) that results from a behavior disorder is possible, video EEG monitoring is required. Depending on the destination, recent travel should prompt testing for bacterial, viral, and parasitic infections that may lead to coma. Clinicians can consider evoked potentials such as brain stem auditory evoked potentials to assess brain stem function or somatosensory evoked potentials to assess the cortex, thalamic, brain stem, and spinal cord pathways (eg after cardiac arrest). 