Arm Weakness? Why Your Brachial Plexus May Be Failing — and What to Do Next

Arm weakness can be unsettling. You may notice difficulty lifting your arm, gripping objects, or even simple tasks like brushing your hair. In some cases, the problem is not in the muscles themselves — it's in the brachial plexus, a complex network of nerves that controls movement and sensation in your shoulder, arm, and hand.

If the brachial plexus is irritated, compressed, inflamed, or injured, your arm may feel weak, numb, painful, or uncoordinated. Understanding what's happening — and what to do next — can help you take the right steps without unnecessary fear or delay.

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What Is the Brachial Plexus?

The brachial plexus is a bundle of nerves that starts in your neck (from spinal nerve roots C5 through T1) and travels down into your shoulder and arm. These nerves:

• Control muscle movement in the shoulder, arm, forearm, and hand
• Provide sensation (touch, temperature, pain) to much of the upper limb
• Coordinate complex hand and arm movements

Because this nerve network is responsible for so much function, even mild problems can cause noticeable symptoms.

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Signs Your Brachial Plexus May Be Involved

Symptoms depend on which part of the brachial plexus is affected and how severe the damage is. Common signs include:

• Arm weakness
• Trouble lifting the arm above the head
• Difficulty gripping or holding objects
• Numbness or tingling in the shoulder, arm, or hand
• Burning or sharp nerve pain
• Muscle shrinking (atrophy) over time
• Loss of coordination

Symptoms may develop suddenly (after trauma or severe pain) or gradually (from compression or inflammation).

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Common Causes of Brachial Plexus Problems

There isn't just one reason the brachial plexus can fail. Causes range from temporary inflammation to serious injuries.

1. Traumatic Injury

This is one of the most well-known causes. It can happen due to:

• Car accidents
• Motorcycle crashes
• Contact sports injuries
• Falls
• Severe shoulder dislocation

In severe trauma, the nerves can stretch, tear, or even detach from the spinal cord. These injuries require urgent medical evaluation.

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2. Neuralgic Amyotrophy (Parsonage-Turner Syndrome)

This is an inflammatory condition affecting the brachial plexus. It often starts with:

• Sudden, severe shoulder or upper arm pain
• Pain lasting days to weeks
• Followed by noticeable arm weakness

The weakness may appear after the pain improves. Some people also experience muscle wasting.

The exact cause isn't always clear, but it may follow:

• Viral illness
• Vaccination
• Surgery
• Immune system activation

If you're experiencing sudden shoulder pain followed by arm weakness, you can use this free AI-powered symptom checker for Neuralgic Amyotrophy to help determine whether your symptoms align with this condition before your doctor's appointment.

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3. Compression or Thoracic Outlet Syndrome

The brachial plexus travels through narrow spaces near the collarbone and shoulder. It can become compressed due to:

• Repetitive overhead work
• Poor posture
• Muscle tightness
• Anatomical variations
• Tumors (rare but possible)

Compression may cause gradual weakness, tingling, and fatigue in the arm.

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4. Tumors or Masses

Tumors in the neck or upper chest — including lung cancers at the top of the lung (Pancoast tumors) — can press on the brachial plexus.

Warning signs that require urgent evaluation include:

• Unexplained weight loss
• Persistent pain that doesn't improve
• Weakness worsening steadily
• Night pain

While tumors are not the most common cause of brachial plexus symptoms, they must be ruled out when red flags are present.

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5. Radiation Injury

People who have received radiation therapy to the chest or neck (often for cancer treatment) may develop delayed brachial plexus damage months or years later.

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When Arm Weakness Is an Emergency

Some symptoms require immediate medical attention. Call emergency services or seek urgent care if you experience:

• Sudden arm weakness along with facial drooping or speech problems (possible stroke)
• Sudden severe neck or arm trauma
• Loss of bladder or bowel control
• Rapidly worsening paralysis
• Severe, unrelenting pain after injury

It's always better to rule out serious causes quickly.

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How Doctors Diagnose Brachial Plexus Problems

A medical evaluation usually includes:

1. Detailed Medical History

Your doctor will ask about:

• Recent injuries
• Infections
• Surgeries
• Vaccinations
• Cancer history
• Timing of pain and weakness

The pattern of symptoms often provides major clues.

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2. Physical Examination

The doctor will test:

• Muscle strength in different arm regions
• Reflexes
• Sensation
• Shoulder stability

Specific weakness patterns help identify which part of the brachial plexus may be involved.

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3. Imaging Tests

Depending on findings, your doctor may order:

• MRI of the neck or brachial plexus
• MRI of the shoulder
• CT scan (if trauma suspected)
• Chest imaging (if tumor suspected)

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4. Nerve Tests

• EMG (electromyography)
• Nerve conduction studies

These tests evaluate how well the nerves and muscles are functioning and help confirm brachial plexus involvement.

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Treatment Options

Treatment depends entirely on the cause.

For Inflammatory Conditions (like Neuralgic Amyotrophy):

• Pain control (NSAIDs or other medications)
• Sometimes corticosteroids (early in the course)
• Physical therapy
• Gradual strengthening exercises

Recovery can take months. Many people improve significantly, though some may have lingering weakness.

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For Compression:

• Physical therapy
• Posture correction
• Activity modification
• Anti-inflammatory treatment
• Surgery (in selected cases)

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For Trauma:

• Observation (if mild stretching injury)
• Physical therapy
• Surgical repair (if nerve torn or avulsed)
• Nerve grafting or transfers in severe cases

Early referral to a specialist improves outcomes in serious injuries.

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For Tumors:

• Oncology referral
• Imaging and biopsy
• Surgery, radiation, or chemotherapy depending on cause

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What Recovery Looks Like

Nerves heal slowly — often about 1 millimeter per day. That means:

• Mild injuries may recover in weeks
• Moderate injuries may take months
• Severe injuries may require surgery or may not fully recover

Physical therapy is essential to:

• Maintain joint flexibility
• Prevent stiffness
• Preserve muscle function
• Support nerve regeneration

Patience is important, but so is follow-up.

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When to Speak to a Doctor

You should schedule a medical appointment if you notice:

• Persistent arm weakness lasting more than a few days
• Severe shoulder pain followed by weakness
• Numbness that does not improve
• Muscle shrinking
• Symptoms after trauma

Speak to a doctor immediately if symptoms are sudden, severe, or accompanied by other neurological changes. Some causes of arm weakness — including stroke or cancer — can be life-threatening and require urgent care.

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The Bottom Line

The brachial plexus plays a critical role in arm movement and sensation. When it fails, you may experience weakness, pain, numbness, or loss of coordination. Causes range from inflammation and compression to trauma or, rarely, tumors.

Most cases are treatable. Many improve with time and therapy. However, ignoring persistent or worsening symptoms can delay recovery or miss a serious diagnosis.

If your symptoms fit the pattern of sudden shoulder pain followed by weakness, consider completing a free online symptom check for Neuralgic Amyotrophy to better understand your situation. Then take the results to your healthcare provider for discussion.

Arm weakness is not something to brush off — but it's also not something to panic about. The right evaluation, early diagnosis, and appropriate treatment make a significant difference.

If you are unsure about your symptoms, or if anything feels severe, unusual, or rapidly worsening, speak to a doctor promptly.