Neurologic diseases are common in the general population, and they will become even more common as the population ages. Therefore, dental patients will regularly present with neurologic conditions. Several diseases affecting the nervous system are of clinical significance in dental practice. These diseases may vary in severity and consequences. The focus of this chapter is on five of the more common and significant neurologic diseases— stroke , Parkinson disease , Alzheimer disease , epilepsy , and multiple sclerosis (MS). Also discussed are cerebrospinal fluid (CSF) shunts because of the assumed risk of bacterial seeding after an invasive dental procedure in patients with such shunts.
CRITICAL COMPLICATIONS: Patients with neurologic diseases are at high risk during dental treatment for complications such as stroke, myocardial infarction (MI), adverse bleeding, altered consciousness, and infection. These events could prove serious or fatal. The dentist must be able to detect these patients, based on history and clinical findings, refer them for medical diagnosis and management, and work closely with their physicians to develop dental management plans that will be effective and safe for these patients.
Stroke (Cerebrovascular Accident)
Stroke is a generic term that is used to refer to a cerebrovascular accident (CVA)—a serious and often fatal neurologic event caused by sudden interruption of oxygenated blood to the brain. The associated ischemic injury results in focal necrosis of brain tissue, which may be fatal if the damage is catastrophic. Even if a stroke is not fatal, the survivor often is debilitated in motor function, speech, or cognition to a certain degree. The scope and health impact of stroke are reflected in the fact that stroke is the leading cause of serious, long-term disability in the United States; 5% of the population older than 65 years of age has had at least one stroke.
Stroke is one of the most significant health problems in the United States. Stroke is the fifth leading cause of death in the United States, with more than 130,000 Americans dying of stroke annually. Each year in the United States, about 800,000 people experience new or recurrent stroke. Three of four of these (600,000) are new strokes. This figure translates to the occurrence of one stroke about every 4 minutes; 75% of persons survive their stroke.
Ischemic stroke accounts for 87% of all strokes in the United States.
An estimated 6.6 million Americans have had a stroke. Overall stroke prevalence during the period from 2009 to 2012 was an estimated 2.6% (National Health and Nutrition Examination Survey, National Heart, Lung, and Blood Institute). According to data from the 2013 BRFSS (Centers for Disease Control and Prevention), 2.7% of men and 2.7% of women had a stroke in this time period.
Hypertension is the most important risk factor for ischemic and hemorrhagic stroke. The incidence of stroke increases directly in relation to the degree of elevation of systolic and diastolic arterial blood pressure above threshold values. More important, conclusive evidence accrued since 1980 indicates that control of hypertension prevents strokes. Metaanalyses of randomized controlled trials confirm an approximate 30% to 40% reduction in stroke risk with lowering of blood pressure.
Approximately 7% to 10% of men and 5% to 7% of women older than 65 years of age have asymptomatic carotid stenosis of greater than 50%. Epidemiologic studies suggest that the rate of unheralded stroke evolving ipsilateral to a stenosis is about 1% to 2% annually.
Nonvalvular atrial fibrillation carries a 3% to 5% annual risk for stroke, with the risk becoming even higher in the presence of advanced age, previous transient ischemic attack (TIA) or stroke, hypertension, impaired left ventricular function, and diabetes mellitus.
Individuals who have a TIA and survive the initial high risk period have a 10-year stroke risk of roughly 19% and a combined 10-year stroke, MI, or vascular death risk of 43% (4% per year). In epidemiologic studies, the risk for stroke in smokers is almost double that in nonsmokers, but the risk becomes essentially identical to that in nonsmokers by 2 to 5 years after quitting. The relative risk for stroke is two to six times greater for patients with insulin-dependent (type 1) diabetes. An association with race has been recognized: Compared with whites, African Americans are at 38% greater risk for a first stroke with a similar greater risk of death. Also, 40,000 more women than men have a stroke each year. Risk of stroke increases with age; however, on average, 28% of people who have a stroke are younger than 65 years of age. There are nearly 5 million stroke survivors living in the United States, and an average dental practice of 2000 adult patients will include about 31 patients who have had or will experience a stroke.
Pathophysiology and Complications
Stroke is caused by the interruption of blood supply and oxygen to the brain as a result of ischemia or hemorrhage. The most common type is ischemic stroke induced by thrombosis (in up to 80% of cases) of a cerebral vessel. Ischemic stroke also can result from occlusion of a cerebral blood vessel by distant emboli. Hemorrhage causes about 15% of all strokes and carries a 1-year mortality rate greater than 60%.
Cerebrovascular disease is the primary factor associated with stroke. Atherosclerosis and cardiac pathosis (MI, atrial fibrillation) increase the risk of thrombolic and embolic strokes, but hypertension is the most important risk factor for intracerebral hemorrhagic stroke. Approximately 10% of persons who have had an MI will have a stroke within 6 years. Additional factors that increase the risk for stroke include the occurrence of TIAs, a previous stroke, high dietary fat, obesity and elevated blood lipid levels, physical inactivity, uncontrolled hypertension, cardiac abnormalities, diabetes mellitus, elevated homocysteine levels, elevated hematocrit, elevated antiphospholipid antibodies, heavy tobacco smoking, increasing age (risk doubles each decade after the age of 65 years), and periodontal disease. Heart failure (see Chapter 6 ) also predisposes the patient to ischemic stroke, the risk for which is twice as high. Increased risk for hemorrhagic stroke also occurs with use of phenylpropanolamine, an α-adrenergic agonist.
Pathologic changes associated with stroke result from infarction, intracerebral hemorrhage, or subarachnoid hemorrhage (SAH). Cerebral infarctions most commonly are caused by atherosclerotic thrombi or emboli of cardiac origin. The extent of an infarction is determined by a number of factors, including the site of the occlusion, size of the occluded vessel, duration of the occlusion, and collateral circulation. The production and circulation of proinflammatory cytokines, the occurrence of clotting factors, and arterial inflammation contribute to platelet aggregation. Neurologic abnormalities result from excitotoxicity, free radical accumulation, inflammation, mitochondrial and DNA damage, and apoptosis of the region supplied by the damaged artery.
The most common cause of intracerebral hemorrhage is hypertensive atherosclerosis, which results in microaneurysms of the arterioles ( Fig. 27.1 ). Vessels within the circle of Willis often are affected ( Fig. 27.2 ). Rupture of these microaneurysms within brain tissue leads to extravasation of blood, which displaces brain tissue, causing an increase in intracranial volume until resultant tissue compression halts bleeding. Hemorrhagic strokes also may be caused by SAH. The most common cause of SAH is rupture of a saccular aneurysm at the bifurcation of a major cerebral artery.
The most serious outcome of stroke is death, which occurs in 8% of those who experience ischemic strokes and 38% to 47% of those with hemorrhagic strokes within 1 month of the event. Overall, about 23% of patients die within 1 year. Mortality rates are directly related to type of stroke, with 80% of patients dying after an intracerebral hemorrhage, 50% after an SAH, and 30% after occlusion of a major vessel by a thrombus. Death from stroke may not be immediate (sudden death) but rather may occur hours, days, or even weeks after the initial stroke episode.
If the victim survives, it is highly likely that a neurologic deficit or disability of varying degree and duration will remain. Of those who survive the stroke, 10% recover with no impairment , 50% have a mild residual disability, 15% to 30% are disabled and require special services, and 10% to 20% require institutionalization. Approximately 50% of those who survive the acute period (the first 6 months) are alive 7 years later.
The type of residual deficit that results from a stroke is directly dependent on the size and location of the infarct or hemorrhage. Deficits include unilateral paralysis, numbness, sensory impairment, dysphasia, blindness, diplopia, dizziness, and dysarthria. Return of function is unpredictable and usually takes place slowly, over several months. Even with improvement, patients frequently are left with some permanent residual problem, such as difficulty in walking, using the hands, performing skilled acts, or speaking. Dementia also may be an outcome of stroke.
Familiarity with the warning signs and symptoms and the phases of stroke can lead to appropriate action that may be lifesaving. Four events associated with stroke are (1) the TIA, (2) reversible ischemic neurologic deficit (RIND), (3) stroke-in-evolution, and (4) the completed stroke. These events are defined principally by their duration.
A TIA is a “mini” stroke that is caused by a temporary disturbance in blood supply to a localized area of the brain. A TIA often is associated with numbness of the face, arm, or leg on one side of the body (hemiplegia) and weakness, tingling, numbness, or speech disturbances that usually last less than 10 minutes. Most commonly, a major stroke is preceded by one or two TIAs within several days of the first attack.
A RIND is a neurologic deficit that is similar to a TIA but does not clear within 24 hours. Eventual recovery is the rule, however.
Stroke-in-evolution is a neurologic condition that is caused by occlusion or hemorrhage of a cerebral artery in which the deficit has been present for several hours and continues to worsen during a period of observation. Signs of stroke include hemiplegia; temporary loss of speech or trouble in speaking or understanding speech; temporary dimness or loss of vision, particularly in one eye (may be confused with migraine); unexplained dizziness; unsteadiness; or a sudden fall.
Clinical manifestations that remain after a stroke vary in accordance with the site and size of residual brain deficits; these include language disorders, hemiplegia, and paresis; the latter is a form of paralysis that is associated with loss of sensory function and memory and weakened motor power. Box 27.1 presents the different behavioral manifestations of right- versus left-sided brain damage. Of note, in most patients with stroke, the intellect remains intact; however, massive left-sided stroke has been associated with cognitive decline.
|Right-Sided Brain Damage||Left-Sided Brain Damage|
Laboratory and Diagnostic Findings
Patients suspected of having had a stroke usually undergo a variety of laboratory tests and diagnostic imaging procedures to rule out conditions that can produce neurologic alterations, such as diabetes mellitus, uremia, abscess, tumor, acute alcoholism, drug poisoning, and extradural hemorrhage. Such investigations often include urinalysis, blood sugar level, complete blood count, erythrocyte sedimentation rate, serologic tests for syphilis, blood cholesterol and lipid levels, chest radiographs, and electrocardiography (ECG). Various abnormalities may be disclosed by the test results, depending on the type and severity of stroke and its causative factors. A lumbar puncture also may be ordered by the physician to check for blood or protein in the CSF and for altered CSF pressure, which would be suggestive of SAH. Doppler blood flow studies, EEG, cerebral angiography, computed tomography (CT) ( Fig. 27.3 ), and magnetic resonance imaging (MRI, including diffusion and perfusion studies of the brain) are important for determining the extent and location of arterial injury.
The first aspect of stroke management is prevention. This is accomplished by identifying specific risk factors (e.g., hypertension, diabetes, atherosclerosis, cigarette smoking) and attempting to reduce or eliminate as many of these as possible. Blood pressure–lowering (see Chapter 3 ), antiplatelet therapy (see Chapter 24 ), and statin therapy are primary stroke prevention methods. Carotid endarterectomy is a secondary stroke prevention method.
The benefit of lowering blood pressure is evident in the fact that a reduction of systolic blood pressure by 10 mm Hg is associated with a one-third reduction in risk for stroke. Regimens of aspirin, ticlopidine, or extended-release dipyridamole are accepted preventive therapies for ischemic stroke in patients who have experienced TIAs or who have had a stroke. Aspirin dosed at 81 to 325 mg daily, can effectively reduce the risk of stroke by preventing emboli. Likewise, surgical intervention through endarterectomy reduces the risk by about 1% per year, such that one stroke is prevented for every 20 patients who undergo surgery over a 5-year period.
Treatment for stroke generally has three components. The immediate task is to sustain life during the period immediately after the stroke. This is done by means of life support measures and transport to a hospital. The second task involves emergency efforts to prevent further thrombosis or hemorrhage and to attempt to lyse the clot in cases of thrombosis or embolism. Thrombolysis and improved neurologic outcomes have been achieved with intravenous (IV) recombinant tissue-type plasminogen activator (rt-PA) and intraarterial prourokinase. Of the two, IV administration of rt-PA within 3 hours of ischemic stroke onset is the only approved therapy in the United States.
After the initial period, efforts to stabilize the patient continue with anticoagulant medications such as heparin, coumarin, aspirin, and dipyridamole combined with aspirin (Aggrenox) in cases of thrombosis or embolism. Whereas heparin is administered intravenously during acute episodes, coumarin, dipyridamole, aspirin, subcutaneous low-molecular-weight heparin, or platelet receptor antagonists (clopidogrel, abciximab, ticlopidine) are used for prolonged periods to reduce risk of thrombosis (e.g., deep vein thrombosis). Corticosteroids may be used acutely after a stroke to lessen the cerebral edema that accompanies cerebral infarction. Such therapy can markedly reduce the likelihood of complications. Surgical intervention may be indicated for removal of a superficial hematoma or management of a vascular obstruction. The latter usually is accomplished by thromboendarterectomy or by use of bypass grafts in the neck or thorax. Diazepam, phenytoin, and other anticonvulsants are prescribed in the management of seizures that may accompany the postoperative course of stroke.
If the patient survives, the third and final task consists of institution of preventive therapy, administration of medications that reduce the risk of another stroke (statins and antihypertensive drugs), and initiation of rehabilitation. Rehabilitation generally is accomplished by intense physical, occupational, and speech therapy (if indicated). Although marked improvement is common, many patients are left with some degree of permanent deficit.
Numerous strategies are being evaluated for treating acute ischemic stroke (AIS). These include intraarterial thrombolysis (IAT); augmentation of rt-PA with other medications, thereby enlarging the therapeutic window (i.e., lengthening the period of efficacy); and neuroprotection. IAT may be a treatment option for selected patients. Possible selection criteria include presentation between 3 and 6 hours from symptom onset, major cerebral artery occlusion, severe neurologic deficits, and high risk of systemic hemorrhage with IV rt-PA (e.g., recent surgery). In most circumstances, the availability of IAT should not preclude the use of IV rt-PA in patients meeting appropriate criteria. IAT requires access to emergent cerebral angiography, experienced stroke physicians, and neurointerventionalists; it should be performed only at a clinical center with considerable expertise in this technique.
The MERCI (Mechanical Embolus Removal in Cerebral Ischemia) retrieval system (Concentric Medical, Inc., Mountain View, CA) has been approved by the U.S. Food and Drug Administration (FDA) for recanalizing acutely occluded cerebral arteries. In the Multi-MERCI study, patients who did not improve immediately after IV rt-PA underwent mechanical embolectomy within 8 hours of symptom onset. Partial or complete recanalization occurred in 74% of patients, with a symptomatic intracerebral hemorrhage rate of 6.7%.
Another, newer FDA-approved device for AIS is the Penumbra stroke system (Penumbra, Inc., Alameda, CA). This device combines two methods of clot extraction, aspiration and mechanical extraction. First the clot is aspirated; then a thrombus removal ring can be used if necessary to remove remaining clot.
Important public health roles of dentists are that of educator in stroke prevention and as an identification of stroke-prone patients. Patients with a history or clinical evidence of hypertension, congestive heart failure, diabetes mellitus, previous stroke or TIA, and advancing age are predisposed to stroke, as well as to MI. As these factors increase in frequency, so does the level of risk ( Box 27.2 ). The dentist should assess patient risk, encourage persons with risk factors to seek medical care, and eliminate or control all possible risk factors (see Box 27.4 ).