7 most common cause(s)
Muscle strength is determined by a complex interplay of nerves, muscle fibers, and chemical messengers. These allow muscles to contract and create force. Anything that disrupts this system can cause weakness of the upper arm. Usually it’s damage to the nerves, such as a pinched nerve in the neck or repetitive strain injury.
It’s difficult to tell true weakness from weakness related to pain, joint problems, or general fatigue that might happen after a hard workout or playing a new sport. True weakness means you have a decrease in muscle power.
You should see your doctor if you’re feeling like your muscles are weak for no apparent reason. It can also be a sign of a stroke, so you shouldn’t ignore it.
Causes
1. Pinched nerve in the neck
Symptoms
- Neck pain only on one side
- Sharp pain that radiates down the arm from the neck and shoulder area
- Numbness and tingling from the neck to the shoulder and upper arm
- Weakness from the shoulder to the hand
A pinched nerve root in the neck (cervical radiculopathy) happens when bones, muscles, or other tissues compress a nerve root, the part of the nerve connected to the spinal cord. It's often from an injury that causes a disc—the spongy tissue between neck bones—to herniate or bulge. The normal wear-and-tear of aging such as arthritis in the neck bones can also cause the problem.
Treating cervical radiculopathy
A pinched nerve root in the neck may improve with rest or changing your activity for a few days or weeks. You can try nonsteroidal anti-inflammatory drugs (NSAIDs) such as ibuprofen (Advil) or naproxen (Aleve).
Physical therapy may help, and in severe cases, you may need steroid injections into the spinal canal.
If these measures don’t relieve your symptoms, you may need surgery to relieve pressure on the nerve root by removing a piece of the herniated disc or cleaning out the bone or cartilage damaged by arthritis.
Pro Tip
Upper arm weakness must be evaluated in its true sense, not just what “feels” weak. —Dr. Michael Gaspar
2. Brachial plexopathy
Symptoms
- Pain in one arm
- Shoulder pain that shoots to the arm
- Arm weakness
- Numbness in one arm
The brachial plexus is a cluster of large nerves between the neck and shoulders. It connects the spinal cord nerves to the nerves in your arms.
Sudden forceful movements that cause the shoulder to stretch down while the neck stretches up and away can injure the brachial plexus. Brachial plexopathy often occurs in contact sports like football (called a shoulder stinger) or from trauma, such as a car or motorcycle accident.
Treating brachial plexopathy
Rest and physical therapy can help you recover from brachial plexopathy. If nerves are permanently damaged, you may need surgery to repair the nerves or remove irritating scar tissue.
3. Stroke or transient ischemic attack (TIA)
Symptoms
- Dizziness
- Leg numbness
- Arm numbness
- Headache
- Weakness, numbness, and paralysis on one side of the face and body
- Slurred speech
- Abnormal vision
A stroke is when blood flow somewhere in the brain has been blocked by a clot. This causes that part of the brain to lose oxygen, which can lead to permanent damage.
A transient ischemic attack (TIA), sometimes called a "mini stroke" or a "warning stroke,” is when a clot has blocked blood flow in your brain, but the clot dissolves on its own and the symptoms go away within minutes.
Because it happens so quickly, a TIA does not cause permanent damage. But it is a warning that a more damaging stroke may occur soon, and you need immediate treatment.
Treating stroke or TIA
If you think that you have had a TIA or a stroke, call 911. The longer you wait to get treated, the greater your chances of having permanent injury or disability.
Your doctor may prescribe thrombolytic medication to dissolve the clots and anticoagulant medication to prevent new clots. You may need surgery to clear your arteries. This can be the case for both TIA or stroke.
4. Thoracic outlet syndrome
Symptoms
- Upper back pain
- Neck pain
- Arm weakness
- Back pain that gets worse when sitting
- Upper spine pain
Thoracic outlet syndrome happens when blood vessels and nerves that travel between the collarbone and the first rib are compressed. Depending on which structures are compressed and how severe it is, you may feel a variety of symptoms.
When nerves are compressed, you may have numbness, tingling, or weakness in your arms. When blood vessels are affected, you may also have discoloration of your hands, cold hands and arms, or pain and swelling.
Thoracic outlet syndrome may come from abnormalities like an extra rib below your collarbone, trauma, repetitive motion, or poor posture (slumped over body position).
Treating thoracic outlet syndrome
Treatment includes addressing the underlying causes and using physical therapy, medication (to reduce pain), and possibly with surgery (to prevent damage to blood vessels). If you have an extra rib bone, you may need surgery to remove it.
5. Multiple sclerosis (MS)
Symptoms
- Severe fatigue
- Vision problems
- Numbness or weakness in arms, legs, or body
- Hypersensitivity, particularly in the arms and legs
- Mobility problems
- Loss of coordination
- Difficulty with speech or swallowing
- Constipation
- Bladder control problems
Multiple sclerosis (MS) happens when the body's immune system attacks nerve fibers and their myelin covering, causing permanent scarring (sclerosis). This damage interferes with the transmission of signals between the brain and different parts of the body.
Doctors don’t know what causes MS, but it usually appears between ages 20 and 50. It is more common in women.
All of the body’s nerves can be affected, so symptoms of MS and how severe they are can vary and they are often unpredictable. Numbness or hypersensitivity of the arms and legs are often the earliest symptoms of MS.
Treating MS
There is no cure for MS, but treatment with corticosteroids and plasma exchange (plasmapheresis) can slow the course of the disease and manage symptoms. This can improve your quality of life. Some drugs, such as disease-modifying drugs, can also be used to slow the progression of MS. They work by changing how your immune system works.
6. Polymyositis (inflammatory myopathy)
Symptoms
- Muscle pain and stiffness
- Muscle weakness
- Joint pain and stiffness
- Trouble catching your breath
- Problems with swallowing
Polymyositis is a disease that causes muscles to become irritated, inflamed, weak, and eventually break down. The condition can affect muscles all over the body, making even simple movements hard to do.
Polymyositis is one in a category of diseases called inflammatory myopathies. While the exact cause of polymyositis isn’t known, people ages 30 to 60 are the most likely to develop it. Polymyositis often comes after a viral illness or autoimmune reaction.
Treating polymyositis
While there is no cure for polymyositis, anti-inflammatory and immunosuppressant medications can help reduce your symptoms. Physical therapy and braces or other assistive devices can help you maintain muscle strength and function.
Pro Tip
A common misconception is that systemic conditions such as the flu cause muscle weakness. Rather, these conditions can lead to the “feeling” of being weak, although muscle power is still normal. —Dr. Gaspar
7. Amyotrophic lateral sclerosis (ALS)
Symptoms
- Muscle twitches in the arm, leg, shoulder, or tongue
- Muscle cramps
- Tight and stiff muscles (spasticity)
- Muscle weakness that affects an arm, a leg, neck or diaphragm
- Slurred and nasal speech
- Difficulty swallowing or chewing
Amyotrophic lateral sclerosis (ALS), also known as Lou Gehrig's Disease, is a degenerative disease that destroys nerve cells. Eventually, it causes total loss of control over muscle function. Doctors don't know what causes ALS.
Treating ALS
There is no cure for ALS, but treatment can help slow the progression of the disease and make you more comfortable. This includes medication, respiratory therapy, physical therapy, occupational therapy, and psychological support.
Other possible causes
A number of conditions may also cause weakness in one upper arm. Systemic disorders may cause physical limitations that are easy to mistake for weakness. But this is usually fatigue, not “true” weakness. These disorders include:
- Diabetes
- The flu
- Cardiopulmonary disease
- Joint disease
- Anemia
- Cancer
- Chronic infections
- Inflammatory diseases
- Depression
Pro Tip
The most important thing for a patient with upper arm weakness to tell their doctor is all of the symptoms they are having in addition to the weakness, particularly when needing to rule out a stroke. —Dr. Gaspar
When to call the doctor
See your primary care doctor if you have any of the following symptoms:
- True muscle weakness that does not improve
- Fever
- Increased heart rate
Should I go to the ER?
Call 911 if you have any of these signs of a stroke:
- Speech difficulty
- Facial drooping
- Weakness to the point you cannot raise your arm
- Sudden vision changes
Treatment and preventative care
At-home care
- Exercising regularly and eating a balanced diet help maintain a healthy weight and blood pressure. It can also decrease the likelihood of developing fatty deposits in your blood vessels, which can lead to clots and eventually, stroke.
Here are some over-the-counter (OTC) options and advice on managing your symptoms and understanding when to seek further medical help.
- Pain Relievers: To manage pain associated with conditions like pinched nerves or muscle strain, OTC pain relievers such as ibuprofen can be helpful.
- Heat Pads: For muscle relaxation and relief from discomfort caused by muscle spasms or tension, consider using heat pads.
Other treatment options
- Physical therapy to restore strength, function, and mobility in the arm.
- Steroid injections into the spinal canal for a pinched nerve that doesn’t improve with anti-inflammatories.
- Immunosuppressants or steroids for polymyositis.
- Surgery, if other treatments don’t work and your symptoms continue to progress or get worse, particularly if you have a pinched nerve.
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