Porth's Essentials of Pathophysiology, 4e

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Nervous System

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There are as many types of status epilepticus as there are types of seizures. Tonic–clonic status epilepticus is a medical emergency and, if not promptly treated, may lead to respiratory failure and death. The dis- order occurs most frequently in the young and old. Morbidity and mortality rates are highest in elderly persons and persons with acute symptomatic seizures, such as those related to anoxia or cerebral infarc- tion. 65 If status epilepticus is caused by neurologic or systemic disease, the cause needs to be identified and treated immediately because the seizures probably will not respond until the underlying cause has been corrected. Treatment consists of appropriate life support mea- sures. Medications are given to control seizure activity. Intravenously administered diazepam or lorazepam is considered first-line therapy for the condition. The prog- nosis is related to the underlying cause as well as the duration of the seizures themselves. spontaneous electrical discharges from neural networks in the brain, thought to result directly or indirectly from changes in excitability of single neurons or groups of neurons.The site of seizure generation and the extent to which the abnormal neural activity is conducted to other areas of the brain determine the type and manifestations of the seizure activity. ■■ Focal seizures originate in a small group of neurons in one hemisphere with secondary spread of seizure activity to other parts of the brain. Seizure activity may involve impairment of consciousness, involuntary motor movements, somatosensory disturbances, special sensory sensations, flushing, tachycardia, diaphoresis, hypotension or hypertension, or pupillary changes due to stimulation of the autonomic nervous system. ■■ Generalized seizures show simultaneous disruption of electrical activity in both hemispheres from the onset.They include unconsciousness and varying bilateral degrees of symmetric motor responses with evidence of localization to one hemisphere. Absence seizures are generalized nonconvulsive seizure events that are expressed mainly by brief periods of unconsciousness. Tonic–clonic seizures involve unconsciousness along with both tonic and clonic muscle contractions. SUMMARY CONCEPTS ■■ Seizures are paroxysmal motor, sensory, or cognitive manifestations of abnormal

Neurocognitive Disorders Neurocognitive disorders involve changes in spectrum of memory and cognitive functions. Memory is the pro- cess by which information is encoded, stored, and later retrieved, while cognition is the process by which infor- mation is reduced, elaborated, transformed, and used. Cognition involves the perception of sensory input and the ability to learn and manipulate new information, recognize familiar objects and recall past experiences, solve problems, think abstractly, and make judgments. Dementia or nonnormative cognitive decline can be caused by any disorder that permanently damages large association areas of the cerebral hemispheres or sub- cortical areas subserving memory and cognition. 66,67 It is a common and disabling disorder in the elderly and, because of the rapidly increasing elderly population, is a growing public health problem. The disorder is charac- terized by impairment of short- and long-term memory, deficits in abstract thinking, impaired judgment and other higher cortical functions, abnormalities of speech, and personality changes. These changes eventually become severe enough that they interfere with day-to-day func- tioning. Common causes of dementia are Alzheimer disease, vascular dementia, frontotemporal dementia, Wernicke-Korsakoff syndrome, and Huntington chorea. The diagnosis of dementia is based on assessment of the presenting problem; history about the person that is provided by an informant (someone who has known the person, usually a family member); complete physi- cal and neurologic examination; evaluation of cognitive, behavioral, and functional status; and laboratory and imaging studies. Depression is the most common treat- able illness that may masquerade as dementia, and it must be excluded when a diagnosis of dementia is con- sidered. This is important because cognitive function- ing usually returns to baseline levels after depression is treated. Screening evaluations for subdural hematoma, cerebral infarcts, cerebral tumors, and normal-pressure hydrocephalus are also recommended. These and other reversible forms of dementia that should be ruled out can be remembered by the mnemonic DEMENTIA: D rugs (drugs with anticholinergic activity), E motional (depression), M etabolic (hypothyroidism), E yes and ears (declining vision and hearing), N ormal-pressure hydro- cephalus, T umor or other space-occupying lesions, I nfection (human immunodeficiency virus infection or syphilis), A nemia (vitamin B 12 or folate deficiency). 67 Alzheimer Disease Dementia of the Alzheimer type is the most common type of dementia. 68–70 The disorder affects more than 5.2 million Americans, and is the sixth leading cause of death. 70 The risk for development of Alzheimer disease (AD) increases with age, starting at a level of 4% of per- sons under age 65 years, 13% of persons 65 to 74 years, 44% of persons 75 to 84 years, and 38% of persons age 85 years or older. 69