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The central nervous system (CNS) is the body's major communication network. Because of localization of functions, neurologic deficits related to disease processes are variable in their presentation. In certain locations of the brain, a lesion will cause minimal or no symptoms, whereas in other areas, it will cause major neurologic deficits. CNS disease can present in many ways, including changes in consciousness, focal neurologic deficits (e.g., aphasia and amnesia, motor and sensory defects), headaches, dizziness, and seizures. Knowledge of the various neurologic pathways will allow a physician to localize the cause of the patient's symptoms.

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CNS diseases are classified within one of many categories, including vascular diseases (e.g., infarcts and spontaneous hemorrhages), trauma, infections, neoplasms, degenerative diseases, toxic and metabolic disorders, and demyelinating diseases. Because the pathology of nervous system diseases is intimately related to their neurologic manifestations, this chapter will begin with a discussion of clinical presentations of central nervous system disorders. This will be followed by a discussion of basic pathologic changes, malformations, vascular diseases, traumatic disorders, infections of the CNS, neoplasms, degenerative diseases, demyelinating disorders, and, finally, a few basic peripheral nerve and skeletal muscle disorders.

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Requirement for consciousness: Intact and functioning brainstem reticular activating system and its cortical projections.

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Terminology for impaired levels of consciousness, in order of increasing severity

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  • Confusion: Impairment of the capacity to think with normal speed and clarity, associated with inattentiveness and disorientation. Delirium is a special example of an acute confusional state in which impaired attention and reasoning are associated with agitation, hallucinations, and in some cases, tremor and convulsions.
  • Drowsiness: Inability to remain awake without external stimulation; often associated with some degree of confusion.
  • Stupor: State in which only vigorous external stimulation can arouse the patient; once aroused, responses remain markedly impaired.
  • Coma: Deep sleep-like state; patient cannot be aroused even with vigorous or repeated external stimulation.

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Causes of change in consciousness

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  1. With abnormal CT scan

    • Hemispheric mass lesions that cross the midline or impinge upon the brainstem.
    • Brainstem lesions that directly affect the reticular formation.
    • Subarachnoid hemorrhage.

  2. With normal CT scan

    • Inflammatory disorders, such as bacterial meningitis and viral encephalitis.
    • Exogenous toxins, such as sedative drugs, alcohols, opioids, and carbon monoxide.
    • Endogenous metabolic insults, such as global hypoxic-ischemic insults, hypoglycemia, hyperammonemia, and hypercalcemia.
    • Postictal state.
    • Selective brainstem ischemia.

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Diagnosis of cause of changes in consciousness: Establishing a differential diagnosis for the cause of a patient's change in consciousness requires evaluation of the history preceding the change, the physical examination, and the effectiveness of initial empirical therapy.

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Categories of cause of changes in consciousness

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  • Toxic and metabolic (e.g., opiate overdose, alcohol).
  • Infectious (e.g., meningitis, encephalitis, septic shock).
  • Cerebrovascular (e.g., stroke).
  • Trauma.
  • Other (e.g., seizures, neoplasms).

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Role of history in diagnosis of changes in consciousness

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  • Preceding headache suggests meningitis, subarachnoid hemorrhage, or encephalitis.
  • Preceding intoxication, ...

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