London: Moving a muscle usually involves communication between the muscle and the brain through nerves. The impetus to move a muscle may originate with the senses. For example, special nerve endings in the skin enable people to determine what something feels like, as when they feel the texture of the fabric or reach in their pocket to find a nickel in an assortment of coins.
This information is sent to the brain, and the brain may send a message to the muscle about how to respond. Also, the amount of muscle tissue must be normal, and the tissue must be able to contract in response to the signal from the nerves. Therefore, true weakness results only when one or more part of this pathway brain, spinal cord, nerves, muscles, or the connections between them is damaged or diseased.
Weakness may develop suddenly or gradually. Weakness may affect all of the muscles in the body or only one part of the body. For example, depending on where the spinal cord is damaged, spinal cord disorders may cause weakness only in the legs.
Symptoms depend on which muscles are affected.
For example, when weakness affects the muscles of the chest, people may have difficulty breathing. When weakness affects muscles that control the eyes, people may have double vision.
Complete muscle weakness causes paralysis.
People may have other symptoms depending on what is causing the weakness. Weakness is often accompanied by abnormalities in sensation, such as tingling, a pins-and-needles sensation, and numbness.
Causes: Because malfunction in the same part of the signal pathway causes similar symptoms regardless of cause, the many causes of muscle weakness are usually grouped by the location of the cause (see table Some Causes and Features of Muscle Weakness). That is, causes are grouped as those that affect the brain, spinal cord, peripheral nerves, muscles, or connections between nerves and muscles. However, some disorders affect more than one location.
Certain conditions that damage muscle, such as a low level of potassium (hypokalemia), consumption of too much alcohol, or use of corticosteroids
- Drugs used to paralyze muscles—for example, to keep people from moving during surgery or while on a ventilator
- For weakness in specific muscles, the most common causes are
- Strokes (the most common cause of weakness affecting one side of the body)
- Nerve damage as occurs in carpal tunnel syndrome or results from injury
- A ruptured or herniated disc in the spine
- Pressure on (compression of) the spinal cord, as can result from cancer that has spread to the spinal cord
- Multiple sclerosis
Fatigue: Many people report weakness when their problem is actually fatigue. Common causes of fatigue include severe illness, cancer, a chronic infection (such as HIV infection, hepatitis, or mononucleosis), heart failure, anemia, chronic fatigue syndrome, fibromyalgia, and mood disorders (such as depression).
Treatment: If the cause is identified, it is treated if possible. If weakness began suddenly and causes difficulty breathing, a ventilator may be used. Physical and occupational therapy can help people adapt to permanent weakness and compensate for the loss of function. Physical therapy can help people maintain and sometimes regain strength.
Essentials for Older People:
Weakness: As people age, the amount of muscle tissue and muscle strength tend to decrease. These changes occur partly because older people may become less active but also because the production of the hormones that stimulate muscle development decreases. Thus, for older people, bed rest during an illness can have a devastating effect.
Compared with younger people, older people start out with less muscle tissue and strength at the beginning of the illness and lose muscle tissue more quickly during the illness. Drugs are another common cause of weakness in older people because older people take more drugs and are more susceptible to side effects of drugs (including muscle damage and problems with nerves).
When evaluating older people who report weakness, doctors also focus on conditions that do not cause weakness but interfere with balance, coordination, vision, or mobility or that make movement painful (such as arthritis). Older people may mistakenly describe the effects of such conditions as a weakness. Regardless of what is causing weakness, physical therapy can usually help older people function better
