Pathological processes active in the nervous system include congenital defects or alterations that may be degenerative, inflammatory, toxic, traumatic, mechanical or neoplastic. Circulatory impairment or disuse will cause impaired function as well.
Cerebrovascular accidents (CVAs)
The majority of CVAs are associated with thrombosis that obstructs blood flow and causes infarction to the area served by the vessel. Tissue served by the affected cerebral artery is destroyed. The neurologic deficits seen depend on the severity and location of the affected tissue but symptoms generally include headache, dizziness, confusion and aphasia (defect in speech).
Embolisms, most often blood clots originating in the heart, cause 8% of all CVAs. The emboli travel to the brain and lodge in the middle cerebral artery most frequently. Classic stroke symptoms of opposite side paralysis, sensory loss, aphasia, apraxia (lack of voluntary movement) and agnosia (lack of recognition) are sudden in onset. Sometimes a weakness of the tunica media in cerebral arteries (congenital or atherosclerotic) causes an enlargement of blood vessels that may subsequently rupture and hemorrhage resulting in the symptoms of stroke.
Alterations of consciousness & functional disturbances
Paralysis is the temporary or permanent loss of motor or sensory function and is a relatively common occurrence with trauma to the nervous system. A flaccid paralysis is characterized by a loss of muscle tone, loss of tendon reflexes, and muscle atrophy. Excessive muscle tone and exaggerated tendon reflexes are characteristic of spastic paralysis. There is no muscle atrophy unless there is prolonged disuse.
Epilepsy is the second most common neurologic disorder after stroke. About 1% of the US population has epilepsy and 80% of the cases can be controlled pharmacologically. This paroxysmal disorder of cerebral function is characterized by sudden, brief seizures and altered consciousness, motor activity and sensory phenomenon. Seizures are defined episodes of brain dysfunction resulting from abnormal neuronal discharge. Such seizures may be the result of microscopic brain lesions, metabolic aberrations, infections, toxic agents or trauma. In 75% of affected adults no cause is identified.
Seizures that affect the entire brain and produce a loss of consciousness, muscle contractions, and possibly incontinence are termed grand mal seizures. Those that are sudden in onset, brief (10-30 seconds) and produce a loss of muscle tone are called petite mal. Petite mal seizures occur mostly in children and may occur up to hundreds of times a day. Partial seizures are those where the electrical disturbance has minimal spread such that normal consciousness and awareness are preserved.
During an attack the person should not be restrained but care should be taken that the local environment is free of things that may cause injury. Swallowing the tongue is not a danger for the epileptic. Do not try to put something in their mouth. The person will require rest after the attack. Anticonvulsant drugs can help control seizures in a majority of cases.
Trauma to the head
Spinal cord injury
The degree of loss of function in spinal cord injuries depends on the level of the injury. Cervical spine injuries above the 4th vertebra may be fatal because control of the diaphragm and intercostal muscles used in respiration is lost. Such high cervical injuries result in quadriplegia. Injuries at the 5th and 6th cervical nerve retain some function of the neck, shoulder and upper arm. Additional elbow, wrist and hand function is seen in individuals with injuries at the 7th and 8th cervical level. Injuries to the thoracic and lumbar spine produce paraplegia. The lower the level of the injury the more function the person retains.
Herniation of the cartilaginous discs that cushion the articulation of the vertebral bodies is most commonly caused by trauma. The central nucleus of the disc is forced out by sudden training of the back causing pain, sensory loss, and paralysis due to pressure on the spinal nerve roots. Most of the time a herniation occurs in the lumbosacral spine between the 4th and 5th vertebrae. Cervical herniations usually occur at between the 5th and 7th cervical nerves resulting in shoulder pain that radiates down the arm and a stiff neck. Initial treatment includes pain relievers, hot packs and bed rest. If the condition does not get better, surgical intervention is warranted.
Generalized symptoms of CNS tumors are headache, vomiting, blurred vision, and papilledema (edema and inflammation of the optic nerve). Other symptoms depend on the location of the tumor. Frontal lobe tumors may produce speech disturbances, apathy, dementia, memory and intellect deficits, diminished judgment, depression, aphasia and apraxia. Tumors of the temporal lobe usually produce sensory aphasia while those of the occipital lobe are characterized by agnosia, paraesthesia, and dyslexia. When the occipital lobe is effected, patients may have visual disturbances, hallucinations and visual agnosia. Cerebellar tumors result in disturbances of equilibrium and coordination.
Sometimes cancer cells originating from a peripheral tumor of the lung, breast or other tissue may enter the CNS and begin to grow. This usually only happens when the metastatic cancer is well advanced. Prognosis for recovery is poor.
Any bacteria may potentially cause meningitis but some are more prominent. Meningitis is an infection of the membranes that surround and protect the brain and spinal cord. Symptoms of such an infection include fever, headache, photophobia, dizziness, neck and back stiffness, drowsiness, stupor and coma. Prompt diagnosis and antibiotic therapy are critical. Diphtheria, tetanus and botulism toxins cause profound effects on the CNS that may be prevented by immunization. Antitoxins are available and may prevent clinical symptoms in many cases.
Fungal infections of the CNS are not very common and usually occur secondary to an infection elsewhere or immunosuppressant therapy. Protozoal infections such as malaria, toxoplasmosis, ambiasis, Chagus, sleeping sickness, and trichinosis (Nematode) can produce CNS produce neurologic symptoms that are acutely fatal or chronic deficits dependent on the causative organism.
Cerebral palsy results from developmental defects in the brain or trauma at birth and is characterized by nonprogressive paralysis occurring on both sides of the body in a symmetrical fashion. Classic symptoms are mental retardation, seizures and motor disabilities with a diagnosis usually occurring in early childhood. The areas of the brain that are damaged determine the clinical picture.
Guillain-Barre Syndrome is an autoimmune disorder that occurs after an infectious disease (usually viral) producing a progressive muscle weakness and paralysis. Both sensory and motor functions are effected by the breakdown of myelin surrounding peripheral nerves. Recovery is usually complete but may take several months. Indeed, most patients (85%) make a full recovery in 4-6 months. Treatments include steroids, ACTH or immunosuppression that are variably effective.
Multiple Sclerosis is a chronic slowly progressive CNS disease where demyelination causes scarring and patches in the tissue. It may be autoimmune in nature. Late signs are nystagmus, tremor, and speech disorders progressing to paraplegia, incontinence and emotional instability.
Amyotrophic Lateral Sclerosis (ALS or Lou Gehrig’s disease) is characterized by muscular weakness and atrophy, spasticity, and hyperflexion due to degeneration of the spinal cord and medullary motor neurons. This steadily progressive disease has a greater incidence in men and usually results in death within 2-6 years although this is sometimes extended to 10+ years depending on where along the spinal cord the degenerative process began and how quickly the medulla becomes involved.
Huntington’s chorea is a dominantly inherited disease of the CNS having an onset at 30-50 years. It is characterized by progressive dementia, bizarre involuntary movements, and abnormal posture. There seems to be an imbalance in several neurotransmitters in parts of the brain. Treatment is usually aimed at blocking neurotransmission via dopamine. A commonly used drug is reserpine. It acts to deplete dopamine by preventing storage within neurons. It has some side effects, however, such as low blood pressure, depression, sedation, diarrhea, and nasal congestion. The disease is uniformly fatal usually within 10-15 years after symptoms appear.
Memory & judgment disorders
Alzheimer’s disease is a presenile dementia caused by an atrophy of the frontal and occipital lobes of the brain. It occurs between the ages of 40 and 60, more often in women than men. There is a progressive, irreversible memory loss, deterioration of intellectual function, disorientation and motor dysfunction. The loss of cholinergic nerve terminals in the basal forebrain is characteristic of Alzheimer’s as are plaques having a core of amyloid protein.