Leg weakness has many causes. Some of them are serious. But most can be treated.

Leg weakness is often a medical emergency that requires prompt medical attention, especially sudden weakness. A quick diagnosis often leads to more effective treatment.

This article explores several reasons for leg weakness and how to tell one from another.

Stroke

A stroke is also called a cerebrovascular accident (CVA). It causes brain damage by interrupting blood flow to a region of the brain. Several areas of the brain work together to move your legs.

Leg weakness from a stroke is:

  • SuddenUsually on just one side

The acronym FAST can help you determine whether you or someone else is having a stroke:

  • Facial drooping: One-sided symptoms of eyelid drooping and downward curving mouth. If the person smiles, does one side droop?Arm or leg weakness: One-sided weakness, can make you drop things, lean while walking, or fall. If they raise both arms, does one drift downward?Speech difficulties: The tongue may be affected by a stroke. Is the speech slurred?Time to call 911: Yes to any of these signs warrants emergency help. Time is a major factor in preventing brain damage. Never “wait and see” about stroke symptoms.

Also watch for:

  • ConfusionDizzinessDouble visionDrowsinessNausea or vomitingSevere headache

If you have a stroke, your best chance of recovery is getting quick treatment.

Guillain-Barre Syndrome

Guillain-Barre syndrome (GBS) is a life-threatening nerve disease. It affects about one in 100,000 Americans per year.

GBS is different from stroke because it affects the nerves, not the brain, and it affects both sides of the body. GBS starts begins with tingling or numbness in both feet.

It then quickly progresses to:

  • Foot weaknessWeakness spreading to the legsEventually, upward-spreading weakness throughout your body

The most dangerous aspect of GBS is weakness of the chest muscles that impair breathing. This can be fatal.

Healthcare providers closely monitor the oxygen levels of people with GBS. You may need to be put on a machine to help you breathe and get enough oxygen until you recover.

Call 911

Get emergency medical help if you have sudden numbness or weakness in your legs or feet.

Medications for GBS can reduce the symptoms and hasten recovery. Most people with GBS survive. But some have persistent leg sensations or moderate weakness for months or years.

Multiple Sclerosis

Multiple sclerosis (MS) is a fairly common neurological illness.

It causes episodes of:

  • WeaknessVision lossSensation disturbancesOther neurological symptoms

MS can cause leg weakness in one or both legs at a time. But it’s more common on just one side.

Symptoms of multiple sclerosis typically come and go. Episodes may last for a few weeks or months. They generally improve but may have some lasting effects.

Early Leg Weakness

MS symptoms tend to be vague at first. One-sided leg weakness can be an early sign, and it may range from mild to severe.

If your symptoms are vague and intermitted, get an appointment with your regular healthcare provider. MS is a serious chronic condition but not usually a medical emergency.

An MS diagnosis takes time and a lot of tests. Several effective treatments are available.

Pinched Nerve

A pinched nerve in the spine can cause leg weakness and/or numbness. It may affect one or both sides.

Generally, a pinched nerve starts with mild or moderate tingling or discomfort and it can slowly get worse. Sometimes, pain and weakness can become severe.

Pinched nerves are often caused by arthritis or spinal inflammation.

Other symptoms of a pinched nerve include:

  • Sharp pain or a dull acheTingling, zinging, pins-and-needles sensationsPain that shoots from your back to your footNumbness in the skin

Sometimes, a pinched nerve can cause sudden leg weakness without a warning. That’s more likely if you’ve had trauma to your spine. Always get emergency treatment for a spinal injury.

It can take some time and work for your healthcare provider to diagnose a pinched nerve.

Treatments include:

  • Physical therapyPain relievers/anti-inflammatory drugsInjected medications

Spinal Cord Disease or Injury

The spinal cord controls your body movements and relays sensation. It’s protected by the spine. Spinal cord damage can lead to leg weakness on one or both sides.

Spinal cord damage is always serious.

It can come from:

  • Spine fracture
  • Herniated disc
  • Cancer spreading to the spine or spinal cord
  • Infection of the spine or spinal cord
  • Multiple sclerosis

A fairly uncommon type of stroke, a spinal cord infarct, affects the spine. It’s caused by bleeding near the spine or a blood clot of the spinal arteries (blood vessels).

Always treat a spinal problem as an emergency. Prompt medical care can prevent permanent damage and leg weakness. 

If you had an accident that damaged your spine, the symptoms will come on suddenly. Other causes may be sudden or gradual. Treatments depend on the specific disease or the type and extent of the injury.

Leg Trauma

A traumatic injury to the leg or pelvic region can result in leg weakness. It could be from damaged muscles, nerves, or joints.

Usually, an injury that severe causes a lot of pain. But if you have severe damage to your spine or a spinal nerve, you might not feel it.

Always get immediate medical attention for any injury that keeps you from walking.

Treatment is generally geared toward repairing the injury. You might need physical rehabilitation to strengthen your leg after it’s healed.

Amyotrophic Lateral Sclerosis

Amyotrophic lateral sclerosis (ALS or Lou Gehrig’s disease) is a relatively uncommon, incurable disease. It generally gets worse within a few years of diagnosis.

ALS causes body weakness but doesn’t interfere with thinking or vision. It typically begins with tingling and weakness, which can be in the legs. Muscle twitches usually occur later as the disease progresses.

This disease affects both sides of the body. Even so, early symptoms may be more noticeable on one side.

ALS weakness can become severe throughout the body. Muscles of the mouth may become too weak for speech. New technologies are making it easier for people with ALS to communicate through eye movements.

Neuropathy

Neuropathy is pain from damaged nerves. It has many causes. It can result in leg weakness if motor nerves are involved.

Symptoms of neuropathy tend to come on gradually and affect both sides.

They include:

  • PainWeaknessNumbnessTinglingLoss of sensation

Neuropathic pain can be severe. It may limit your mobility and other activities. Common causes include uncontrolled diabetes, alcohol, and nutritional deficiency.

See your healthcare provider if you sometimes have odd sensations in your feet or legs. Neuropathy can be managed but usually not reversed. So it’s important to get a diagnosis before the damage progresses.

Myopathy

Diseases of the muscles are called myopathies. They usually manifest with weakness of the arms, legs, hands, or feet.

Examples of myopathies are:

  • Polymyositis
  • Lyme disease
  • Thyroid or parathyroid disease
  • Inflammatory diseases such as lupus and rheumatoid arthritis
  • Amyloidosis
  • Muscular dystrophy

Some of these are genetic. Others are not, and may develop during adulthood. They can impact one or both legs.

Myopathy symptoms generally start gradually and progress over time. Some types of myopathy may become severe within a few days or weeks of starting.

It can be diagnosed with electromyography (EMG) and nerve conduction studies. Treatments can include supportive braces, physical therapy, and medications.

Toxins

A number of toxins can cause leg weakness.

  • Lead poisoning
  • Chemotherapy medications
  • Statins (cholesterol-lowering drugs)
  • Steroid drugs
  • Antivirals
  • Alcohol

Weakness is likely to affect both legs.

If you develop weakness after starting a new medication, tell your healthcare provider right away. You may be experiencing toxicity.

Cancer

Cancer is one of the least likely causes of leg weakness. Rarely, leg weakness can be the first sign of a brain or spinal tumor.

Cancer can also metastasize (spread) to the brain or spine, causing leg weakness. Symptoms can be sudden and may affect one side or both.

Let your healthcare provider know about your symptoms right away. Most tumors can be effectively treated with surgery, radiation, and/or chemotherapy. A spinal cord compression from a metastatic tumor may require urgent treatment with high-dose steroids.

Summary

Leg weakness has many causes. Many of them are serious. Some are medical emergencies.

Get immediate medical attention for:

  • Sudden weaknessStroke symptoms (facial drooping, weak limbs, slurred speech)Weakness or numbness that starts in the feet and moves upwardKnown or suspected spinal injuriesInjuries that prevent walkingLeg weakness that develops after you have already been diagnosed with cancer

Gradual-onset weakness always warrants a visit to your healthcare provider. Often, catching the problem early can keep it from getting worse.

A Word From Verywell

Leg weakness can be scary, especially if it’s sudden. Be sure to get prompt medical attention for new or worsening leg weakness.

The wide range of causes means that diagnosis is necessary before a treatment plan can begin. It’s vital to get medical attention for leg weakness, even if symptoms are not severe.

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By Heidi Moawad, MD

Heidi Moawad is a neurologist and expert in the field of brain health and neurological disorders. Dr. Moawad regularly writes and edits health and career content for medical books and publications.