Brachial neuritis is a condition where nerves running from the neck through the shoulder and down the arm become inflamed, causing sudden, severe shoulder pain followed by muscle weakness. Also called Parsonage-Turner syndrome, it affects roughly 1.6 people per 100,000 each year and is more common in men between ages 30 and 70. Though the pain can be intense and alarming, the condition is self-limiting, and most people recover motor function over a period of months to more than a year.
What Causes It
The exact cause of brachial neuritis remains unclear, but it appears to involve an immune-mediated inflammatory attack on the brachial plexus, the network of nerves that controls sensation and movement in the shoulder, arm, and hand. In 30 to 85% of cases, a triggering event can be identified 3 to 14 days before symptoms begin. Known triggers include viral infections, recent surgery, and vaccinations. Cases have been documented after tetanus shots, and the CDC considers brachial neuritis occurring 2 to 28 days after tetanus vaccination a reportable event. Autoimmune mechanisms and bacterial infections have also been linked to the condition.
There is also a hereditary form, though it is far less common. In many cases, no clear trigger is ever identified, and the condition is labeled idiopathic.
How Symptoms Develop
The hallmark of brachial neuritis is its two-phase pattern. In 70% of patients, the condition begins with sudden, severe, aching pain in one shoulder that can radiate into the neck, arm, and forearm. This pain often strikes at night and can be intense enough to wake you from sleep. It typically lasts an average of four weeks, though in rare cases it resolves within 24 hours. About 10% of patients experience pain lasting longer than eight weeks.
As the pain fades, muscle weakness and wasting set in. In most people, noticeable weakness develops a few weeks after pain begins, though about 30% experience weakness within the first 24 hours alongside the pain. The muscles around the shoulder blade and upper arm are most commonly affected, and visible shrinkage of those muscles often becomes apparent within three to four weeks of symptom onset. You may notice difficulty lifting your arm, reaching overhead, or carrying objects.
Brachial Neuritis vs. Similar Conditions
The pain pattern of brachial neuritis can closely mimic other problems, which is why it’s frequently misdiagnosed at first. The conditions most often confused with it are cervical radiculopathy (a pinched nerve in the neck) and rotator cuff injuries.
A few key differences help distinguish them. With a pinched nerve in the neck, pain is usually triggered or worsened by certain head and neck positions, numbness and tingling follow a predictable nerve path down the arm, and turning or tilting the head toward the painful side reproduces symptoms. In brachial neuritis, the pain is rarely positional, sensory changes like numbness are not a major feature, and the pattern of weakness doesn’t follow a single nerve root the way a disc herniation would.
Shoulder conditions like rotator cuff tears, bursitis, and frozen shoulder can also cause unilateral pain and limited range of motion. The distinguishing factor is that none of these produce neurological deficits like the distinct muscle wasting and weakness seen in brachial neuritis.
How It’s Diagnosed
There is no single test that confirms brachial neuritis. Diagnosis relies heavily on recognizing the characteristic clinical pattern: acute shoulder pain that gives way to weakness and muscle wasting. Your doctor will perform a neurological exam testing strength, reflexes, and sensation in the affected arm.
Nerve conduction studies and electromyography (EMG) can help confirm which nerves are involved and assess the severity of damage. These tests are most useful a few weeks after symptoms begin, once nerve changes have had time to develop. MRI of the shoulder or brachial plexus may be ordered primarily to rule out other causes, such as a disc herniation in the cervical spine or a structural problem in the shoulder joint.
Treatment and Recovery
During the acute pain phase, treatment focuses on pain control. Over-the-counter anti-inflammatory medications and prescription pain relievers are commonly used. Some physicians prescribe a short course of oral corticosteroids, though evidence for their effectiveness in changing the overall course of the disease is limited. The priority in the early weeks is keeping you comfortable while the inflammation runs its course.
Physical therapy is central to recovery and follows a progressive approach based on your current strength. When you have little or no muscle contraction in the affected arm, the focus is on passive range-of-motion exercises, where a therapist moves your joints through their full range to prevent stiffness and joint contracture. As some muscle activation returns, you transition to active-assisted movements where you do part of the work with help. Eventually, as strength improves, you take over the full range of motion independently and begin adding resistance exercises.
This progression matters because pushing weakened muscles too hard too early can cause further damage, while doing too little risks letting joints stiffen and muscles weaken further from disuse.
What Recovery Looks Like
Recovery from brachial neuritis is slow but generally favorable. Motor function typically returns over a period of 6 to 18 months, with gradual improvement as the damaged nerves regenerate. The rate of recovery depends on the severity of nerve damage and which specific nerves were affected.
The muscle wasting that develops during the weakness phase can look dramatic, particularly around the shoulder blade and upper arm. This visible atrophy usually improves as nerve function returns, though rebuilding full muscle bulk takes time and consistent rehabilitation. Some people experience residual weakness or fatigue in the affected arm even after the main recovery period, particularly with overhead activities or sustained exertion. The condition is more common on the right side, and while recurrence is possible, it is not typical.