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Key Features

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Essentials of Diagnosis
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  • Reduction or alteration in cognitive and affective mental functioning and in arousability or attentiveness

  • Acute onset

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General Considerations
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  • The neurologic substrate for consciousness is the ascending reticular activating system in the brainstem, which extends the thalamus and paraventricular nucleus of the hypothalamus

  • Large lesions of the cortex, especially bilateral lesions, can also cause coma

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Clinical Findings

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Symptoms and Signs
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  • Many terms, including obtundation, lethargy, somnolence, stupor, light coma, and deep coma, are used to describe the continuum from fully alert and aware to complete unresponsiveness

  • Persistent vegetative state

    • Denotes a chronic condition in which there is preservation of the sleep-wake cycle

    • However, there is no awareness of self or the environment

    • No recovery of mental function

  • Minimally conscious state

    • Denotes patients who do not meet criteria for persistent vegetative state

    • These patients occasionally may have purposeful movements

  • Brain death refers to patients in coma without brainstem reflexes or spontaneous respirations

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Differential Diagnosis
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  • Locked-in syndrome

    • Describes patients who are conscious but have no access to motor or verbal expression because of massive loss of motor function of the pontine portion of the brainstem

    • Vertical eye movements may be preserved

  • Akinetic-mutism

    • Patient is aware, but does not initiate movement or follow commands

    • Caused by lesions of the frontal lobes

  • Catatonia

    • Refers to patients with psychiatric illness

    • Patients retain ability to maintain trunk and limb postures

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Diagnosis

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Laboratory Findings and Diagnostic Procedures
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  • If the cause of the coma is not obvious, emergency laboratory tests must be obtained

  • Initial tests include

    • An immediate blood glucose

    • Complete blood cell count

    • Urine obtained by catheterization if necessary

    • pH and electrolytes (including bicarbonate)

    • Serum urea nitrogen

    • Aspartate aminotransferase

    • Ammonia

  • Urine, blood, and even gastric contents must be saved for toxin screen if the underlying cause is not obvious

  • Blood culture and lumbar puncture often are necessary to rule out CNS infection

    • Papilledema is a relative contraindication to lumbar puncture prior to imaging

    • Often, a blood culture is obtained, antibiotics started, and imaging study of the brain done prior to a diagnostic lumbar puncture

    • If meningitis is suspected and a lumbar puncture is delayed or believed to be hazardous, antimicrobials should be started and the diagnostic lumbar puncture done later

  • Tests that are helpful in obscure cases of coma include

    • Oxygen and carbon dioxide partial pressures

    • Serum and urine osmolality

    • Porphyrins

    • Lead levels

    • General toxicology screen

    • Serum amino acids

    • Urine organic acids

  • Rarely, an emergency EEG aids in diagnosing the cause of coma

    • May correlate with the stage of coma and add prognostic information

    • Should be ordered if seizures are suspected

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Imaging
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  • If severe head trauma or increased pressure is suspected, an emergency CT scan or MRI is necessary

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