Demyelinating Disorders of the Central Nervous System

Multiple sclerosis (MS)

• Multiple sclerosis (MS) is a primary central nervous system (CNS) demyelinating disorder that spares the peripheral nervous system. The disease occurs twice as often in females than males. It usually affects individuals between the ages of 20 and 50.

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• The pathophysiology of multiple sclerosis is T-cell autoimmunity to CNS myelin with subsequent inflammation, and the formation of demyelination plaques and axonal degeneration. In its early stages, the inflammation (and so the symptoms) wax and wane; however, chronic disease with gliosis (scarring) results in gradual neurologic deterioration.

 

clinical Manifestations —The clinical manifestations of MS usually begin in a remitting-relapsing pattern, with “attacks” occurring during increases in body temperature and serum calcium levels. The specific neurologic deficits depend on the parts of the CNS that are most affected by the disease.

• Mixed or General MS — Complications in mixed or general MS are usually visual, but can include brain stem and cognitive dysfunction.

• Spinal MS — Causes weakness and/or numbness, and bladder and bowel problems.

• Cerebellar MS — Causes disorders in gait and motor movements. Paroxysmal attacks most often include paresthesias (especially with flexion of the neck), dysarthria, and ataxia.

• Most individuals eventually develop a progressive-relapsing pattern of deterioration over several decades.
– Evaluation and Management — MS is diagnosed by history, physical examination, MRI findings, and increased levels of IgG in the cerebrospinal fluid. Treatment includes anti-inflammatory and immunosuppressive drugs, such as corticosteroids and interferon.

 

Amyotrophic lateral sclerosis (ALS)

• Amyotrophic lateral sclerosis (ALS), also known as Lou Gehrig disease, is a degenerative disorder of both upper and lower motor neurons causing progressive muscle weakness and wasting. This devastating disorder affects both men and women, usually during the fifth decade of life, and leads to inexorable deterioration of neurologic function without cognitive decline.

• Pathophysiology
The pathophysiology of ALS is associated with a defect in a gene on chromosome 21, which leads to defective glutamate metabolism. Glutamate is an excitotoxin that causes degeneration of both upper and motor neurons without inflammation. Axonal degeneration is followed by gliosis (scarring) and denervation of motor units.

 

• Clinical Manifestations
Individuals with ALS experience progressive muscle weakness and atrophy with both flaccid and spastic paralysis. This weakness progresses to involve the muscles of respiration, eventually causing respiratory failure, which requires mechanical ventilation. On average an individual with ALS lives 2 to 3 years after development of symptoms.

 

• Alzheimer disease (AD) is the most common cause of late-onset dementia in the United States. Its prevalence increases with age, and risk factors include family history, history of head trauma, and alcohol abuse. Although the etiology is not known, toxins, viruses, and submicroscopic proteinaceous infectious particles called prions have been implicated.

• The pathophysiology of Alzheimer disease includes defects in chromosomes 19 and 21, which may be carried in the mitochondrial DNA.

• Abnormal amyloid proteins and apolipoprotein E (APOE) are linked with both structural changes and functional changes in the brain.

• The structural changes found in Alzheimer disease include neuritic plaques and neurofibrillary tangles.

• High levels of the excitotoxins glutamate and aspartate are released, which stimulate N-methyl-D-aspartate (NMDA) receptors and lead to more neuronal damage.

• Typical perfusion defects in the posterior temporal and parietal regions can be visible on a SPECT image The functional changes of AD include decreased synaptic levels of acetylcholine.

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Parkinson disease

• Parkinson disease is a common movement disorder that occurs because of degeneration of the basal ganglia and the dopaminergic nigrostriatal pathway. Secondary causes of Parkinson disease include trauma, infection, drugs, or toxins. Primary Parkinson disease is more common in men and most often afflicts individuals in their late 50s and early 60s.

 

• Pathophysiology
The pathophysiology of Parkinson disease is still being explored. Neuronal degeneration in the basal ganglia and in the nigrostriatal pathways leads to a decrease in central nervous system dopamine and a relative increase in acetylcholine.

 

• Clinical Manifestations
This dopamine/acetylcholine imbalance affects muscle tone, causing hypertonia (resting tremor and rigidity) and akinesia (lack of normal movement). Additional clinical manifestations include postural disturbance, frequent falls, dysarthria, dysphagia, slurred speech, drooling, and urinary retention. A decline in cognitive function and dementia is common, as is depression.

 

Meningitis

• meningitis can be caused by many types of microorganisms, including viruses, fungi, protozoans, and rickettsiae, the most serious type of infection is caused by bacteria. Bacterial meningitis can occur in immunocompromised individuals such as infants, the elderly, those on immunosuppressive drugs, or individuals with AIDS. However, the bacteria also can attack otherwise healthy young adults.

• Streptococcus pneumoniae (see image on the right) is the most common cause of community-acquired bacterial meningitis in the United States. Haemophilus influenza meningitis is much less common since the widespread vaccination of children. In young adults, Neisseria meningitidis (also known as meningococcus) is a highly contagious and serious cause of meningitis, often occurring in epidemics. Vaccination for this dangerous organism is recommended for those living in close quarters with others, such as college students and military personnel.

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