Arm Weakness: Signs, Causes, Treatment, and More

Arm weakness refers to a loss of muscle and strength in the arm, causing difficulty moving or using it. Arm weakness is usually a symptom of other underlying conditions or injuries. Depending on the cause, it may occur immediately, randomly, or develop gradually. Some causes may present a significant health risk.

Moving your arm requires communication between your muscles, brain, and nerves. If communication falters, you may experience weakness or be unable to move your arm as usual.

This article will explain arm weakness and the different potential causes. It will also describe accompanying symptoms and when to seek medical advice.

Arm weakness refers to a loss of strength in the arm and the inability to move an arm because of decreased muscle strength or affected arm muscles.

It can happen spontaneously or progress slowly over time. Weakness in the arm may occur on one or both sides of the body and may accompany weakness in other body parts. Additionally, it may occur with various other symptoms, including arm pain.

If you have arm weakness, you may have difficulty moving the affected arm or performing daily tasks.

Arm weakness can arise from various conditions that affect the muscles, bones, joints, nervous system, or metabolism.

Arm weakness can accompany generalized weakness, which is common with certain hereditary disorders, or it may result from a specific injury to the arm.

Arm weakness may be caused by damage to the muscles or bones of the arm or certain muscular and skeletal conditions, including:

• Arm injury: This can be a traumatic or specific injury to the arm that may cause weakness.
• Arthritis: This is a condition in which joints in the body are inflamed, making them stiff and painful. There are many types of arthritis, and joint pain may lead to weakness in the arms or other body parts.
• Cyst: This is usually a benign sac located on the body. It can contain fluid, air, or other materials.
• Fractured or broken bone: Fractures or damage to bones in the body can often lead to weakness, even after healing.
• Infection of the arm’s soft tissues: There are many infections of soft tissues in the arm that may stem from a wound or a bite. These infections can lead to weakness in the arms.
• Muscular dystrophy: This is an inherited disorder that causes muscle weakness and a progressive loss of muscle tissue.
• Myopathy: This is another muscle condition that results in muscle weakness.
• Tendinitis: This occurs when the tendons in the body are inflamed.

Arm weakness can also be caused by problems with the nervous system, including:

• Amyotrophic lateral sclerosis: Also known as Lou Gehrig’s disease, this is a severe neuromuscular disease that causes muscle weakness and disability.
• Carpal tunnel syndrome: This is a repetitive stress injury in which repeated wrist movement can lead to pain, numbness, and disability of the hands.
• Cerebral palsy: This group of disorders impairs movement, balance, and posture.
• Multiple sclerosis: This disease affects the brain and spinal cord, causing weakness, coordination, balance difficulties, and other problems.
• Myasthenia gravis: This is an autoimmune neuromuscular disorder that causes muscle weakness.
• Radiculopathy: This is the compression of a nerve in the spine, resulting from a spinal nerve root injury.

A variety of systemic conditions can also cause arm weakness, including:

• anemia, which is a low red blood cell count that may cause weakness
• electrolyte imbalance
• fibromyalgia, a chronic condition that causes pain, stiffness, and tenderness
• heavy metal poisoning, such as lead poisoning
• malnutrition
• thyroid problems
• toxic ingestion, such as eating poisonous plants, mushrooms, or chemicals
• age, as muscle strength and tissue decrease over time

In some cases, arm weakness may be a symptom of a serious or life threatening condition. These conditions include:

• brain tumor
• severe infection, accompanied by a fever higher than 101^oF
• stroke
• transient ischemic attacks, which are temporary stroke-like symptoms that may be a warning sign of an impending stroke

While arm weakness is usually not serious, arm weakness can indicate a stroke. 

You should seek immediate medical care if you experience serious symptoms that may indicate a stroke, such as:

• sudden, severe headache
• loss of consciousness
• confusion
• sudden numbness or paralysis, particularly on one side of the body
• vision changes
• difficulty speaking

If your arm weakness is persistent or causes you concern, seek prompt medical care.

Read more about stroke signs here.

Arm weakness may accompany other symptoms, depending on the underlying disorder or condition.

Arm weakness may accompany other symptoms affecting the musculoskeletal system, including:

• lumps on the arm
• difficulty breathing
• fatigue
• muscle pain
• reduced mobility or range of motion in the joints
• shoulder, arm, hand, or finger pain
• swollen joints

Arm weakness may accompany other symptoms affecting the nervous system, which includes the brain, nerves, and spinal cord. These symptoms include:

• confusion or loss of consciousness
• difficulty chewing, swallowing, or speaking
• muscle spasms
• numbness or tingling
• paralysis

Arm weakness may accompany symptoms related to other body systems, including:

• fatigue
• fever
• itching
• malaise or lethargy
• redness, warmth, or swelling

In some cases, arm weakness may be a symptom of a life threatening condition, such as a stroke or serious infection, that should be evaluated immediately in an emergency setting. 

You should seek immediate medical care if you, or someone you are with, have any of these life threatening symptoms, including:

• change in the level of consciousness or alertness, such as passing out or unresponsiveness
• garbled or slurred speech
• high fever
• paralysis or inability to move a body part
• sudden weakness, numbness, or tingling on one side of the body
• vision changes or vision loss
• severe headache

To diagnose your condition, your doctor or licensed healthcare practitioner may ask you several questions related to your arm weakness, including:

• How long have you felt weakness in your arm?
• Do you have any other symptoms?
• Have you had any recent infections?
• Have you had any recent injuries?
• Do you have a family history of autoimmune disorders, such as multiple sclerosis?

Doctors may perform different tests, depending on where they think the issue stems from. This includes:

• MRI scans to check for brain disorders
• lumbar puncture for spinal disorders
• electromyography for nerve disorders or neuromuscular issues
• blood cell count tests
• blood tests to evaluate liver and kidney condition

Arm weakness itself is not usually a serious condition. Mild arm weakness may be temporary and may resolve spontaneously.

Because arm weakness can occur due to serious conditions, a lack of treatment can result in complications and permanent damage.

Once doctors diagnose the underlying cause, it is important to follow your unique treatment plan. A treatment plan can help reduce the risk of potential complications, including:

• paralysis
• permanent loss of coordination, sensation, or both
• spread of cancer or infection

Optimal treatment for arm weakness depends on the underlying cause of the weakness. In some cases, physical therapy may help to improve arm strength.

If arm weakness occurs with pain, medication may assist in resolving both symptoms.

Arm weakness can refer to the loss of muscle strength or movement ability in the arm. There can be many different causes of weakness in the arm, ranging from mild injury to a potentially serious condition, such as multiple sclerosis or a stroke.

It can happen gradually over time, such as with old age, or can be a sudden, immediate occurrence. It is important to seek medical advice if you experience any symptoms, such as breathlessness or paralysis. These symptoms may indicate a more serious condition.