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Muscle Diseases

Definition Muscle diseases, which are also called myopathies, are disorders of skeletal muscle structure or function. Myopathies can be primary and occur in isolation, or they can be part of a multisystem disorder. Epidemiology Many muscle diseases ( Table 389-1 ) are inherited as autosomal dominant, autosomal recessive, X-linked, or maternal (mitochondrial) conditions. Environmental factors that may precipitate myopathies include recent infection, foreign travel, exposure to…

Peripheral Neuropathies

Approach to Peripheral Neuropathy The term peripheral neuropathy is used to describe a group of disorders that are caused by injury to the peripheral nervous system, which encompasses the final pathways of motor, sensory, and autonomic function. Epidemiology As a group, peripheral neuropathies are among the most common neurologic problems encountered in medical practice. The prevalence of peripheral neuropathy increases with age from 2 to 3%…

Amyotrophic Lateral Sclerosis and Other Motor Neuron Diseases

Definition The motor neuron diseases ( Table 387-1 ) are a heterogeneous group of disorders in which selective loss of function of upper motor neurons, lower motor neurons, or both results in impairment of the nervous system’s control of voluntary movement. The most common acquired motor neuron disease, amyotrophic lateral sclerosis (ALS), is a combined upper and lower motor neuron disorder. The features of lower motor…

Autonomic Disorders

Systemic Autonomic Disorders Definition Autonomic dysfunction, which is an important cause of disability, accompanies many diseases that affect the central or peripheral nervous system. It may manifest as autonomic failure or autonomic hyperactivity, may be generalized or focal, and may have a subacute, chronic progressive, or intermittent temporal profile. The prognosis of autonomic disorders depends on the underlying condition. Epidemiology The most common causes of autonomic…

Developmental and Neurocutaneous Disorders

The understanding of many neurodevelopmental disorders has improved dramatically because of high-resolution neuroimaging, which can detect structural defects that previously went unrecognized, genetic testing, and a better grasp of molecular mechanisms. As a result, targeted treatments are now available for some conditions. Neural Tube Defects The worldwide incidence of neural tube defects is about 1 to 10 per 1000 live births. In the United States, neural…

Nutritional and Alcohol-Related Neurologic Disorders

Vitamins and minerals, which are essential to cellular function, must be obtained from the environment because the body cannot produce them. They are necessary for embryonic and early development as well as the subsequent maintenance of metabolic function of both the central and peripheral nervous systems. Deficiencies can cause a variety of neurologic syndromes ( Table 384-1 ), each with a well-described constellation of symptoms that…

Encephalitis

Definition Encephalitis is a diffuse or focal inflammation of the parenchyma of the brain. The term encephalitis indicates that the predominant clinical syndrome arises from infection and inflammation in the parenchyma of the brain rather than in the leptomeninges. When both the leptomeninges and brain parenchyma are involved, the term meningoencephalitis is used. In the United States, about 50% of cases of encephalitis are viral in…

Brain Abscess and Parameningeal Infections

A brain abscess affects the brain’s parenchyma directly, whereas parameningeal infections produce suppuration in potential spaces covering the brain and spinal cord (epidural abscess and subdural empyema) or produce occlusion of the contiguous venous sinuses and cerebral veins (cerebral venous sinus thrombosis). Brain Abscess Epidemiology The frequency of various causes of brain abscess ( Table 382-1 ) in the population is difficult to ascertain because of…

Meningitis: Bacterial, Viral, and Other

Bacterial Meningitis Definition Meningitis is an inflammation of the arachnoid membrane, the pia mater, and the intervening cerebrospinal fluid (CSF). The inflammatory process extends throughout the subarachnoid space around the brain and spinal cord and involves the ventricles. Pyogenic meningitis is usually an acute bacterial infection that evokes a polymorphonuclear response in CSF. By comparison, tuberculous meningitis ( Chapter 299 ) is often subacute and characterized…

Multiple Sclerosis and Demyelinating Conditions

The disorders of myelin encompass a wide range of diseases in which myelin is not produced (hypomyelination), myelin is not formed in a normal fashion (dysmyelinating disease), or normally formed myelin is destroyed or not maintained appropriately (demyelinating disease and myelinolysis) ( Table 380-1 ). Hypomyelinating and dysmyelinating diseases are uncommon and include an array of leukodystrophies that have a genetic basis and may affect the…

Other Movement Disorders

Definition Movement disorders are first divided into hypokinetic and hyperkinetic categories. Hypokinetic disorders , which are characterized by akinesia, bradykinesia, and rigidity, are parkinsonian syndromes and are discussed in Chapter 378 . The common hyperkinetic movement disorders ( Table 379-1 ) are defined by specific clinical phenomena. TABLE 379-1 HYPERKINETIC MOVEMENT DISORDERS Tremor Chorea Ballism Dystonia Athetosis Tics Myoclonus Startle Stereotypies Miscellaneous Clinical Manifestations and Diagnostic…

Parkinsonism

Parkinsonism is a clinical syndrome that consists of four cardinal signs: tremor, rigidity, akinesia, and postural disturbances. Parkinson disease is a common cause of the syndrome, but there are numerous other causes ( Table 378-1 ). TABLE 378-1 DIFFERENTIAL DIAGNOSIS OF PARKINSONISM Modified from Cloutier M, Lang AE. Movement disorders: an overview. In: Factor SA, Lang AE, Weiner WJ, eds. Drug Induced Movement Disorders . Malden,…

Hemorrhagic Cerebrovascular Disease

In the United States, about 13% of strokes are caused by intracranial hemorrhage, but the worldwide percentage is about 20% because of countries where hypertension is common but atherosclerosis is less common. Intracerebral hemorrhage, which accounts for about 75% of cases, usually occurs when small penetrating arteries rupture and produce a focal collection of blood within the parenchyma. Subarachnoid hemorrhage, which accounts for about 25% of…

Ischemic Cerebrovascular Disease

Definition Ischemic cerebrovascular disease is caused by a reduction of blood supply to the brain. The injury may be focal (related to occlusion of a single artery), multifocal (related to occlusion of several arteries), or global. Although certain clinical features (e.g., severe hypertension, headache, impaired consciousness) may suggest brain hemorrhage ( Chapter 377 ) rather than ischemia, it is not possible to differentiate the two types…

Approach to Cerebrovascular Diseases

Definition The term cerebrovascular disease refers to a group of conditions in which the brain or spinal cord is injured by a vascular cause. The onset is generally abrupt, but it also can be insidious. Clinical manifestations depend on the location and extent of damage to neural structures. Although risk factors and treatments may overlap, cerebrovascular diseases are pathophysiologically divided into those in which an insufficiency…

Sleep Disorders

Definition Sleep is an active state of decreased responsiveness during which multiple vital functions occur to promote higher cognitive functioning and overall good health. During this physiologic state, the brain restores several metabolic processes, clears waste products, and furthers synaptic reorganization to promote alertness, memory, and learning. To achieve these goals, the brain cycles through discrete stages of sleep that allow progressive revitalization to support neuronal…

Coma, Disorders of Consciousness, and Brain Death

Disorders of consciousness and limited responsiveness ( Table 373-1 ) encompass a range of conditions, from mild encephalopathy or confusion to coma and brain death. Although not all causes of encephalopathy lead to poor outcomes, the rapid and comprehensive evaluation of a patient with altered consciousness remains one of the most important goals in all of medicine. Depending on the cause, a patient with altered mental…

The Epilepsies

Definition A seizure is defined by transient focal or generalized signs or symptoms due to abnormal excessive or synchronous neuronal activity in the brain. Focal seizures, which originate within neuronal networks limited to one cerebral hemisphere, produce signs and symptoms corresponding to the specific region of the brain affected by the seizure. Generalized seizures rapidly affect extensive neuronal networks on both cerebral hemispheres, and their signs…

Cognitive Impairment and Dementia

The Spectrum of Mild Cognitive Impairment to Dementia Definition Dementia is a cognitive disorder that leads to interference with daily functioning and results in loss of independence ( Table 371-1 ). Dementia can range in severity from mild, when a patient may still be independent in a few activities, to severe, when total dependence occurs. Mild cognitive impairment is the term that describes the earlier phase…

Regional Cerebral Dysfunction: Higher Mental Functions

Definition Higher mental function is at the core of what defines competent, independent individuals. Impairment of higher mental function can be broadly classified into four categories. Intellectual developmental disorder is a form of cognitive impairment that is present from infancy. Acquired forms of cognitive impairment are delirium, dementia, and focal cognitive disorders. Delirium ( Chapter 361 ) is defined by its acute or subacute onset and…