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More Diseases & Conditions
More Diseases & Conditions Articles
Influenza (the flu) is a respiratory infection. It is caused by the influenza virus. Influenza typically is spread by air or by direct contact from one person to another. Influenza virus is very contagious.
Most influenza cases occur during epidemics. Epidemics peak during the winter months. A particularly widespread and severe epidemic is called a pandemic.
Compared with other viruses, influenza can strike remarkably large numbers of people in a relatively short time. In the developed nations, about 10-15% of the people get the flu each year. During severe epidemics, a greater fraction of the population gets sick.
The most common types of influenza virus are A and B. Influenza A is the one usually responsible for the annual epidemics. Most people get multiple flu infections during their lives. With many other types of infections, having the disease once protects against a second infection. That is because the body's immune system remembers the returning virus. It attacks it immediately, and rapidly eliminates it.
With influenza, the virus usually has mutated (changed) somewhat since the first infection. The change is enough to fool your immune system. As a result, the immune system responds slowly. By the time the immune response is in full gear, millions of the body's cells are already infected.
Tendons are tough, flexible, fibrous bands of tissue that connect muscles to bones. When tendons become inflamed, irritated or suffer microscopic tears, the condition is called tendonitis. Tendons can be small, like the delicate, tiny bands in the hands, or large, like the heavy, ropelike cords that anchor the calf or thigh muscles. In most cases, the cause of tendonitis is unknown; when a cause can be identified, the condition usually happens for one of two reasons:
Overuse – A particular body motion is repeated too often.
Overload – The level of a certain activity, such as weightlifting, is increased too quickly.
Rarely, tendonitis is caused by an infection, such as gonorrhea. Tendonitis is most common in the shoulder, elbow, knee, wrist and heel, although it can happen anywhere that tendons are found in the body. For uncertain reasons, tendonitis is also common in people with diabetes. In recent years, a rare cause of tendonitis (or other tendon disease, including rupture) has been recognized: the use of certain antibiotics, including ciprofloxacin or levofloxacin. Why this happens is unknown.
Bedwetting, also called nocturnal enuresis, means that a child accidentally passes urine at night during sleep. Because this is normal in infants and very young children, bedwetting is not considered a medical problem unless it happens in a child who is already in elementary school or who was completely dry day and night and then began to wet the bed again during the night.
By age 5, 80% to 85% of children are consistently dry throughout the night. After age 5, the number of children who continue to wet the bed decreases by about 15% per year, even without treatment. Only 1% of children still wet the bed by the time they are 15 years old.
To help make diagnosis and treatment easier, doctors sometimes classify bedwetting into two types, primary and secondary nocturnal enuresis. In primary nocturnal enuresis, the child has never been consistently dry at night. In secondary nocturnal enuresis, the child has been dry at night for at least three to six months (or one year, according to some experts) and has begun to wet the bed again. It is very important to remember that in both types, the child is not wetting the bed on purpose.
Lead is a metal that is poisonous (toxic) when inhaled or eaten. Lead gets into the bloodstream. It is stored in the organs, tissues, bones and teeth.
With increasing or prolonged exposure, lead can cause:
Permanent damage to the central nervous system, especially the brain
Delayed development in children
Behavioral changes in children
Decreased production of red blood cells (anemia)
Damage to the reproductive systems of men and women
The leading source of exposure to lead is lead-based paint. This was outlawed for residential use in 1978. But it remains in some older homes. The main hazard is paint dust. Paint dust enters the air when old paint is scraped, sanded or begins to flake.
People can get lead into their bodies in other ways. These include:
Drinking water from pipes that are made of lead or use lead solder
Using ceramic dishes made with lead
Using products made with lead-containing paint (often imported from other countries)
Playing in lead-contaminated soil
Using lead in hobbies or crafts such as making stained glass
Using certain home remedies that contain lead
Eating lead-contaminated spices purchased in foreign countries (unusual)
Children face the most serious risk. Their growing bodies absorb more lead. Young children, especially toddlers, tend to put objects in their mouths that may be covered with lead dust. If lead paint is flaking, small children sometimes eat the sweet tasting paint chips. Or they chew on painted surfaces, such as window sills.
Adults who have high lead levels in their blood usually were exposed in the workplace. Industries with a high potential for exposure include:
Construction that involves welding, cutting, blasting or other disturbances of surfaces painted with lead
Radiator repair shops
Young children can be exposed to lead when parents who work in these areas carry lead dust home on their clothes and shoes.
A woman who had lead poisoning can pass lead on to her fetus if she becomes pregnant. This remains true even if she no longer is exposed to lead.
Since lead was banned in gasoline and residential paint, average blood levels of lead have dropped dramatically in the United States.
In children, lead levels of 5 micrograms or more per deciliter (mcg/dL) of blood are known to be hazardous. Recent studies suggest that even lower levels may be harmful. Pediatricians closely monitor children whose lead level is approaching 5 (mcg/dL). They are encouraged to look carefully for possible sources of lead exposure.
Fragile X syndrome is an inherited disorder associated with mental retardation and a particular appearance. It is caused by an error in a small piece of the DNA (genetic blueprint) for the FMR1 gene. This gene is found on the X chromosome, one of the two chromosomes (X and Y) that determine gender.
In people with fragile X, a particular section of the DNA code — CGG — is "fragile" and gets repeated an unusually large number of times, compared with the normal 5 to 50 times. As a result, the FMR1 gene is not expressed (turned on), and the body cannot produce FMR1 protein, which is related to nerve function.
Depending on the number of CGG repetitions, fragile X can have a variety of physical, intellectual and behavioral effects. People with more repetitions tend to have more severe symptoms. For example, people with 200 or more CGG repetitions are described as having a full fragile X mutation and usually develop many of the symptoms of fragile X syndrome, including mental retardation. People with 59 to 200 CGG repetitions are described as having a fragile X premutation and may not show any obvious signs or symptoms of fragile X syndrome. The number of CGG repetitions can increase when the gene is passed from generation to generation, increasing the chance of developing the full fragile X mutation.
Fragile X syndrome is seen in approximately 1 in 4,000 to 6,000 males and 1 in 8,000 to 9,000 females. However, many more people carry the fragile X premutation, but show no signs or symptoms of the syndrome. Fragile X syndrome is the most common inherited cause of mental retardation in males.
Malignant hyperthermia is a severe reaction to a dose of anesthetics. The reaction is sometimes fatal. It is caused by a rare, inherited muscle abnormality. Infrequently, extreme exercise or heat stroke can trigger malignant hyperthermia in someone with the muscle abnormality.
In people with the muscle abnormality, muscle cells have an abnormal protein on their surfaces. The protein does not affect muscle function significantly. That is, until the muscles are exposed to a drug that can trigger a reaction.
When a person with this condition is exposed to one of these drugs:
Calcium stored in muscle cells is released
The muscles contract and stiffen at the same time
There is a dramatic and dangerous increase in body temperature (hyperthermia)
Malignant hyperthermia usually occurs during or after surgery. But it can occur wherever anesthetic medications are used. This includes:
Intensive care units
Symptoms of malignant hyperthermia usually occur within the first hour after exposure to the trigger medication. However, the symptoms can be delayed for up to 12 hours.
Most cases occur in children and adults younger than 30.
A subdural hematoma occurs when a blood vessel near the surface of the brain bursts. Blood builds up between the brain and the brain's tough outer lining. The condition is also called a subdural hemorrhage.
In a subdural hematoma, blood collects immediately beneath the dura mater. The dura mater is the outermost layer of the meninges. The meninges is the three-layer protective covering of the brain.
A subdural hematoma is a life-threatening problem because it can compress the brain.
Most subdural hemorrhages results from trauma to the head. The trauma damages tiny veins within the meninges.
In young, healthy people, bleeding usually is triggered by a significant impact. This type of impact might occur in a high-speed motor vehicle accident.
In contrast, older people may bleed after only a minor trauma. For example, it might happen from falling out of a chair.
A subdural hematoma is also more common in people:
Taking medications that thin the blood
Who abuse alcohol
Who have seizures
An acute subdural hemorrhage is bleeding that develops shortly after a serious blow to the head. Blood accumulates rapidly, causing pressure to rise within the brain. This can result in loss of consciousness, paralysis or death.
When bleeding develops slowly, it is known as a chronic subdural hemorrhage. Bleeding may develop over a period of weeks to months
This form of bleeding is much more common in older people. The head trauma that causes chronic subdural hemorrhage is often minor. Many of those affected cannot recall a head injury.
Malaria is an infection caused by single-celled parasites that enter the blood through the bite of an Anopheles mosquito. These parasites, called plasmodia, belong to at least five species. Most human infections are caused by either Plasmodium falciparum or Plasmodium vivax.
Plasmodium parasites spend several parts of their life cycle inside humans and another part inside mosquitoes. During the human part of their life cycle, Plasmodium parasites infect and multiply inside liver cells and red blood cells.
Some infected blood cells burst because of the multiplying parasites inside. Many more infected red blood cells are broken down by your spleen or liver, which filter out and remove damaged or aging red blood cells from circulation. Both Plasmodium parasites in the bloodstream and irritants that are released from broken red blood cells cause malaria symptoms.
Most deaths from malaria are caused by P. falciparum, which causes severe disease. Before P. falciparum malaria causes a red blood cell to burst, it can make the surface of the cell stick to other cells like it. This causes the blood to clot within small blood vessels, which can severely damage organs.
People who have lived all their life in a country with a high rate of malaria have typically been exposed to malaria parasites many times. After the first exposure, your immune system begins to protect you, so re-infection may cause few or no symptoms.
Your immune system does not remain active against malaria for more than a few years if you are not exposed again. This explains why people can live for years in the tropics without being bothered by malaria. However, people from the tropics who spend several years in another country may lose their immune protection.
A subarachnoid hemorrhage is bleeding from a damaged artery at the surface of the brain. This bleeding often causes a sudden, severe headache. It is a medical emergency. Subarachnoid hemorrhage is a type of stroke. It can cause permanent brain damage.
Blood from a subarachnoid hemorrhage pulses into the space between the brain and the skull. It mixes with the cerebrospinal fluid that cushions the brain and spinal cord. As blood flows into the cerebral spinal fluid, it increases the pressure that surrounds the brain. The increased pressure can interfere with brain function.
In the days that immediately follow the bleeding, chemical irritation from clotted blood around the brain can cause brain arteries to go into spasm. An artery spasm can cause additional new brain damage.
Most often, a subarachnoid hemorrhage happens because a bulge in the wall of an artery ruptures. The sac-like bulge is called a saccular aneurysm. A subarachnoid hemorrhage also can occur because blood leaks from an abnormal tangle of blood vessels called an arteriovenous malformation (AVM).
Several large arteries form a circle at the base of your brain. When a subarachnoid hemorrhage is caused by a ruptured saccular aneurysm, the aneurysm usually is located where a blood vessel branches from one of these large arteries. About 20% of patients who have had a subarachnoid hemorrhage have multiple aneurysms.
Although it is not possible to predict whether an aneurysm will rupture, an aneurysm is more likely to rupture when it has a diameter of 7 millimeters or more. In most cases, a person who has a brain aneurysm never has a symptom related to it.
Scarlet fever is an infection caused by Group A Streptococcus ("strep") bacteria. It causes a finely textured rash that can appear like sandpaper along with other symptoms. It usually occurs after a strep infection of the throat (strep pharyngitis, or strep throat), but occasionally after a strep skin infection. The rash of scarlet fever is caused by a toxin that the strep bacteria produce.
Scarlet fever once was common among children ages 2 to 10, but now it is relatively rare. The reason for this remains a mystery, especially because there has been no decrease in the number of cases of strep throat or strep skin infections.