Merck Manual

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Some Causes and Features of Muscle Weakness

Some Causes and Features of Muscle Weakness

Cause

Common Features*

Tests

Brain disorders

Headaches, personality changes, confusion, difficulty concentrating, drowsiness, loss of balance and coordination, and paralysis or numbness

Sometimes seizures

MRI or CT of the brain

Multiple sclerosis (affects the brain, spinal cord or both)

Usually other symptoms of nervous system malfunction (such as loss of sensation, loss of coordination, and vision problems)

Weakness that

  • Tends to come and go

  • Sometimes affects different parts of the body

  • Is worse in hot weather

MRI of the brain and sometimes of the spinal cord

Sometimes a spinal tap (lumbar puncture)

Symptoms that occur suddenly:

  • Weakness or paralysis, usually on one side of the body

  • Abnormalities in or loss of sensation on one side of the body

  • Difficulty speaking, sometimes with slurred speech

  • Confusion

  • Dimness, blurring, or loss of vision, particularly in one eye

  • Dizziness or loss of balance and coordination

A doctor’s examination

CT or MRI of the brain

Spinal cord disorders

Acute transverse myelitis (sudden spinal cord inflammation), often due to

  • Multiple sclerosis

  • Inflammation of blood vessels

  • Certain infections such as Lyme disease or syphilis

Tingling, numbness, and muscle weakness that

  • Occur rapidly (over hours to a few days)

  • Start in the feet and move upward

Usually a bandlike tightness around the chest or abdomen

Often difficulty passing urine

When an injury is severe, loss of bowel and bladder control and/or reduced sexual response, including erectile dysfunction in men

MRI or CT of the spinal cord

A spinal tap

Blood tests to help identify the cause

Cauda equina syndrome, caused by pressure on several spinal nerve roots, as may result from

Weakness in both legs

Loss of feeling in the upper inner part of the thighs, the buttocks, bladder, genitals, and the area between them (saddle area)

Usually pain in the lower back

Loss of bowel and bladder control and/or reduced sexual response, including erectile dysfunction in men

MRI or CT of the spinal cord

Compression of the spinal cord that develops suddenly (acute), as may result from

  • Abscesses (pockets of pus)

  • Hematomas (pockets of blood)

  • Injuries of the neck or back

  • Some cancers

Symptoms that develop in hours or days

Weakness or paralysis of the legs and sometimes arms and loss of sensation

With abscesses or tumors, tenderness to the touch over the compressed area

MRI or CT of the spinal cord

Compression of the spinal cord that develops slowly (chronic), as may result from

  • Cervical spondylosis (degeneration of the vertebral disks due to arthritis)

  • Spinal stenosis (narrowing of the passageway for the spinal cord) due to arthritis

  • Some tumors

Symptoms that are present for weeks to months

When an injury is severe, loss of bowel and bladder control and/or reduced sexual response, including erectile dysfunction in men

MRI or CT of the spinal cord

Compression of a spinal nerve root by a ruptured disk

Weakness, numbness, or both in one leg or arm

Usually back or neck pain that shoots down the leg or arm

Usually MRI or CT of the spinal cord

Usually electromyography (stimulating muscles and recording their electrical activity)

Sometimes nerve conduction studies (measuring how fast nerves transmit signals)

Multiple sclerosis (affects the brain, spinal cord, or both)

Usually other symptoms of nervous system malfunction (such as loss of sensation, loss of coordination, and vision problems)

Weakness that

  • Tends to come and go

  • Sometimes affects different parts of the body

  • Is worse in hot weather

MRI of the brain and spinal cord

Sometimes a spinal tap

Disorders that affect the peripheral nerves and the brain or spinal cord§

Progressive muscle weakness that

  • Often starts in the hands

  • Sometimes affects one side more than the other

Clumsiness, involuntary muscle contractions, and muscle cramps

Drooling and difficulty speaking and swallowing

As the disorder progresses, difficulty breathing and eventually death

Electromyography and sometimes nerve conduction studies

Often MRI of the spinal cord to rule out spinal cord disorders that can cause similar symptoms

Muscles that tire easily and progressive muscle weakness

Sometimes muscle twitching and loss of muscle tissue

In people who have had polio

Electromyography and sometimes nerve conduction studies

Disorders that simultaneously affect many nerves (polyneuropathies)

Weakness and often loss of sensation that

  • Usually begin in both legs

  • Then progress upward to the arms

When severe, difficulty swallowing and breathing

Electromyography and nerve conduction studies

A spinal tap

Nerve damage caused by

Muscle weakness that

  • Often begins in both feet

  • Then affects the hands

  • Then progresses up the legs and arms

Loss of sensation, typically before muscles become weak

Loss of reflexes

Electromyography and nerve conduction studies

Other tests depending on the disorder suspected, such as

  • Urine tests to check for toxins

  • Blood tests to check for certain antibodies or to measure sugar, vitamin, or drug levels

  • Sometimes a spinal tap

Muscle wasting (atrophy)

Sometimes loss of reflexes

Loss of sensation, including the ability to sense position of the limbs, vibration, pain, and temperature

Electromyography and nerve conduction studies

Genetic testing

Disorders that affect the connections between nerves and muscles (neuromuscular junction disorders)

Botulism (due to the bacteria Clostridium botulinum)

At first, often a dry mouth, drooping eyelids, vision problems (such as double vision), difficulty swallowing and speaking, and rapidly progressive muscle weakness, often beginning in the face and moving down the body

When contaminated food is the source, nausea, vomiting, stomach cramps, and diarrhea

No changes in sensation

Blood or stool tests to check for toxins produced by the bacteria

Sometimes electromyography

Sometimes examination of a stool sample to check for bacteria

Weak and drooping eyelids, double vision, difficulty speaking and swallowing, and weakness in the arms and legs

Excessive weakness of affected muscles that

  • Occurs after muscles are used

  • Disappears when they are rested

  • Recurs when they are used again

Use of a drug (edrophonium test) to see whether it improves muscle strength after muscles are used

Blood tests to check for certain antibodies and/or electromyography

Tearing of the eyes, blurred vision, increased salivation, sweating, coughing, vomiting, frequent bowel movements and urination, and weak muscles that twitch

A doctor’s examination

Sometimes blood tests to identify the toxin

Botulinum toxin when a dose that is too high is used to treat dystonia or other muscle spasms

Weakness of the treated muscles or sometimes of all muscles

A doctor's examination

Disorders that affect muscles (myopathies)§

Muscle malfunction due to use of alcohol, corticosteroids, or various other drugs

Weakness that tends to first cause difficulty standing up or lifting the arms overhead

Use of a drug that can cause muscle damage (such as a statin)

When due to use of alcohol or certain other drugs, muscle aches and pains

A doctor’s examination

Stopping any drug that can cause muscle malfunction

Sometimes electromyography

Blood tests to measure levels of muscle enzymes that leak from damaged muscles into the blood

Viral infections that cause muscle inflammation

Muscle aches and pains that are worsened by movement, especially walking

Sometimes fever, a runny nose, cough, sore throat, and/or fatigue

Sometimes only a doctor’s examination

Sometimes blood tests that measure the amount of muscle damage

Muscle biopsy (removal of a piece of muscle tissue for examination under a microscope)

Conditions that cause generalized muscle wasting:

Loss of muscle tissue

In people with obvious evidence of the problem

A doctor’s examination

Electrolyte abnormalities due to certain disorders or use of diuretics:

Weakness that

  • Affects the whole body

  • May come and go

  • Is often accompanied by muscle cramping and twitches

Blood tests to measure the level of potassium and other electrolytes

(such as Duchenne muscular dystrophy and limb-girdle muscular dystrophy)

Progressive muscle weakness that

  • May start during infancy, childhood, or adulthood

  • Depending on the type, may progress rapidly, causing early death

In some types, an abnormally curved spine (scoliosis) and weakness of the spinal muscles, which often develop during childhood

A thorough family history to determine whether any family members have had a similar disorder

Genetic testing

Muscle biopsy

X-rays of the spine to check for scoliosis

*Features include symptoms and results of the doctor's examination. Features mentioned are typical but not always present.

Symptoms vary depending on the location (level) of the damage. Areas that are supplied by the parts of the spinal cord below the damaged part are affected (see figure Where Is the Spinal Cord Damaged?).

In the United States, MRI is usually available. However, if MRI is unavailable, myelography with CT (x-rays taken after a radiopaque contrast agent is injected via a spinal tap) can be done.

§Sensation is usually not affected.

CT = computed tomography; MRI = magnetic resonance imaging.