Hemiparesis

Hemiparesis is one-sided muscle weakness. It happens because of disruptions in your brain, spinal cord or the nerves that connect to the affected muscles. It’s a symptom you shouldn’t ignore because it can be a symptom of a stroke. If it happens suddenly, you should get immediate medical attention.

Overview

Hemiparesis is weakness that affects one side of your body. It can affect your face, arm, leg or a combination of all three.
Hemiparesis is one-sided muscle weakness. It's usually a symptom of a brain-related issue or condition. It can affect the face, arm and leg, and sometimes it affects all three.

What is hemiparesis?

Hemiparesis is one-sided muscle weakness. It’s a key symptom of neurological (brain- or nervous system-related) problems. Some of those problems are life-threatening medical emergencies. However, hemiparesis can also happen with conditions that aren’t dangerous.

If you experience sudden hemiparesis in a limb or your face for an unknown reason, you should immediately go to the nearest emergency room (ER). Having this symptom unexpectedly can be an early sign of a stroke. You should also seek immediate medical help if you have any other signs of stroke, including balance issues, vision changes, face and arm drooping and speech difficulties.

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Possible Causes

What are the most common causes of hemiparesis?

When you have hemiparesis, the affected side of your body doesn’t have the same strength level as the opposite side. That can happen for two reasons:

  • A problem in your brain: When part of your brain isn’t functioning properly, one-sided weakness is one of the possible symptoms.
  • A problem with your spinal cord or nerves: The spinal cord and nerves are like your body’s wiring. They carry signals to and from your brain, including signals that command your muscles to move. If something affects the wiring, the signals can’t reach their destination properly, affecting how strongly the muscles follow orders.

The side of your body that hemiparesis affects depends on where the problem is in your central nervous system (CNS). Your brain and spinal cord make up the CNS, but the side of your body they link to depends on a quirk of your body’s structure.

Anatomy of the central nervous system

A major part of how your CNS works depends on “decussation.” This term comes from “decussis,” the Latin word for the Roman numeral “X.” This term comes into play because there’s a point where the nerve tissue in your spinal cord “decussates.” The nerve fibers cross like an X and switch sides. Decussation happens in the brainstem, just above where your skull and spine connect.

When the problem with your CNS happens above the decussation point (in your brain), you experience hemiparesis on the opposite (contralateral) side. When hemiparesis happens because of a problem below the decussation point (somewhere in your spinal cord or peripheral nervous system), the hemiparesis symptoms happen on the same (ipsilateral) side as the problem.

The only exceptions are when the problem is in an area that relies on nerves that connect to your brain without passing through the decussation point. These points are mainly in your head and face.

Conditions that cause hemiparesis

Dozens of conditions and circumstances can cause hemiparesis. Some of the most common causes include:

Care and Treatment

How is hemiparesis treated?

The treatments for hemiparesis depend on the underlying cause. Some of these conditions are treatable or even curable. Others may get better on their own. Unfortunately, many of these conditions (such as spinal cord or traumatic brain injuries) can permanently damage affected parts of your nervous system. In these cases, the hemiparesis won’t go away, although it may improve to some degree.

Because there are so many different ways to treat hemiparesis, a healthcare provider is the best person to tell you more about the possible treatments in your situation. They can give you information that considers your specific condition, circumstances, health history and more.

What can I do at home to treat hemiparesis?

Hemiparesis can be a sign of a stroke. Because of that, it’s not something you should diagnose or self-treat.

The only exception is if a healthcare provider previously diagnosed you with a condition that can cause hemiparesis. Migraines or seizures are examples of this.

Talk to your healthcare provider if you have a condition that can cause hemiparesis. They can tell you when this symptom is a sign that you need medical attention immediately.

What are the possible complications or risks of not treating hemiparesis?

Because hemiparesis is a possible stroke symptom, the risks of not treating it can be high. In the worst cases, it can result in permanent brain damage, paralysis, loss of abilities or even death.

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Can hemiparesis be prevented?

Hemiparesis can happen unpredictably and for reasons that aren’t fully understood. Because of that, it’s not preventable. However, you can reduce your risk of it happening by avoiding conditions or events that can cause hemiparesis. Key ways to avoid those conditions and events include:

  • Eat a balanced diet, and reach and maintain a weight that’s healthy for you. Many conditions related to your circulatory and heart health, especially stroke, can cause brain damage that leads to hemiparesis. Preventing stroke and similar conditions is key to reducing your risk of developing this symptom.
  • Manage your health conditions. Chronic conditions like Type 2 diabetes, high blood pressure and epilepsy can raise your risk for conditions or injuries that could cause hemiparesis. Managing these conditions is essential to lowering your risk of developing this symptom. You should also take care to manage conditions that can cause gradual damage to your nervous system, such as multiple sclerosis.
  • Don’t ignore infections. Infections can cause hemiparesis if they spread to your brain. Getting prompt treatment for infections — especially ones in your eyes, ears and nose — is essential. Be sure to follow treatment guidelines as closely as possible, too.
  • Wear safety equipment. Protective gear, especially helmets and safety restraints (such as seat belts), can help you avoid head, neck and back injuries that could lead to hemiparesis.

When To Call the Doctor

When should hemiparesis be treated by a doctor or healthcare provider?

Hemiparesis should always be diagnosed and treated by a healthcare provider the first time you have it. If they diagnose you with a condition that involves hemiparesis but isn’t dangerous, they can tell you the things to watch for that mean you need medical attention.

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Additional Common Questions

Hemiplegia vs. hemiparesis — what’s the difference?

Hemiplegia and hemiparesis are very similar symptoms, and many people — including healthcare providers — use the terms interchangeably.

  • Hemiparesis is one-sided weakness.
  • Hemiplegia is one-sided paralysis. Having it means you can’t move the affected body part(s) at all. Hemiplegia is more severe than hemiparesis.

What is ataxic hemiparesis?

Ataxic hemiparesis is when you have combined symptoms of weakness and difficulty coordinating movements. It’s generally a symptom of small-vessel blockages in your brain (lacunar stroke).

A note from Cleveland Clinic

Having hemiparesis can be a scary experience, especially if it’s something you’re unfamiliar with. When it happens suddenly and unexpectedly, it’s usually a sign that you need medical attention immediately. If you experience hemiparesis or are with someone who has one-sided muscle weakness, don’t panic. Conditions that cause this symptom to appear suddenly are serious but are often very treatable if you get immediate care. With quick diagnosis and treatment, you improve the chances of having a positive outcome and returning to your usual routine and activities.

Medically Reviewed

Last reviewed by a Cleveland Clinic medical professional on 05/04/2023.

Learn more about our editorial process.

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