Acute brachial plexus neuritis, neuralgia amyotrophy, or Parsonage Turner syndrome, is a clinically defined syndrome that consists of sudden severe,
acute, sharp, throbbing, or burning pain in the shoulder girdle and upper arm with no apparent cause. The pain usually is constant, but it is exacerbated
by movements of the shoulder. Movements of the neck, coughing, and/or sneezing usually do not worsen the pain. After days or weeks, the pain subsides, to
be followed by weakness (within about 2 weeks of onset) and even muscle wasting in the upper arm. The weakness is usually maximal at onset but can progress
over 1 or more weeks. Numbness may occur, depending on the particular nerves affected, and usually is found in the nerve distribution corresponding to
maximal muscle weakness. However, numbness is rarely a prominent complaint.
The pathophysiology of brachial neuritis is unknown, but the condition is generally thought to be an immune-mediated inflammatory reaction against nerve fibers
of the brachial plexus. Studies have suggested that various infections (viral [particularly of the upper respiratory tract] or less commonly, bacterial
[pneumonia, diphtheria, typhoid]) precede the onset of acute brachial plexus neuritis in as many as 25% of cases. Up to 15% of cases have been reported to occur
following vaccinations. Other possible causal factors such as surgery, trauma (not related to the shoulder), childbirth, medical investigative procedures
(lumbar puncture, radiologic dye), and systemic illness (e.g., polyarteritis nodosa, lymphoma, systemic lupus erythematosus, temporal arteritis, Ehlers-Danlos syndrome)
have been less commonly implicated. In 30-85% of the cases, a suspected precipitating factor can be found 3-14 days before the initial onset of the pain.
The disorder is often mistaken for other disorders affecting the shoulder region, including cervical radiculopathy, adhesive capsulitis, shoulder arthritis,
calcifying tendonitis, or other rotator cuff problems, or Herpes Zoster. Disorders causing muscle wasting or weakness, especially nerve root compression,
spinal cord or brachial plexus tumors, anterior poliomyelitis or amyotrophic lateral sclerosis should also be considered in the differential diagnosis.
Evaluation with electrodiagnostic and radiographic studies is useful in confirming the diagnosis and excluding alternative disorders. MRI of the clinically weak
muscles may reveal high signal intensity of the affected muscles on the T2 study. These changes may appear within days following the onset of symptoms and
persist for months. An MRI scan of the plexus and muscles of the shoulder girdle or upper arm is seldom required to establish a diagnosis, but it may be
useful if an early, specific diagnosis would be beneficial. A cervical spine MRI can aid in the diagnosis of suspected cervical radiculopathy.
Electromyographic testing in patients with acute brachial plexus neuritis yields variable data, depending on the severity of neural damage and the timing of the examination.
Most cases of acute brachial plexus neuritis occur between 20 and 60 years of age. The male-to-female ratio ranges from 2:1 to >10:1. The incidence has been estimated as
1-2 cases per 100,000 persons, but this figure is probably low as many cases are misdiagnosed, or the symptoms are mild and clinically unrecognized.
The usual abnormality on physical examination is a brachial plexus lesion, as indicated by involvement of two or more nerves. Weakness commonly occurs in the supraspinatus,
infraspinatus, deltoid and/or the biceps muscles.
Brachial plexus neuritis following immunization against smallpox, tetanus toxoid, diphtheria, tetanus and pertussis (DTP), influenza, and hepatitis B have been reported.
The exact etiology of post-vaccination brachial plexus neuritis is unknown. Direct injury to the nerve is unlikely because often the not-injected limb can be involved.
Moreover, an injection in the deltoid muscle can lead to an axillary nerve injury, but, in many cases larger parts of the brachial plexus are involved.
The course of the neuritis is usually one of gradual improvement and recovery of muscle strength in 3 to 4 months. Some patients, however, experience several years of
muscle weakness or a slight permanent weakness. In general, 80% of patients with brachial neuritis recover functionally within 2 years; 90% recover functionally within 3 years.
Brachial neuropathy is treated conservatively and largely symptomatically. While the pain is present, pain relievers (analgesics) should be freely given.
The pain may be severe enough for chronic (weeks of) narcotic therapy. A short course of high-dose oral steroids is often recommended, however immunosuppressive therapy
(e.g., steroids, immunoglobulin, plasma exchange) has not been shown to be beneficial.
Physical therapy for 3 to 8 weeks should be focused on the maintenance of full range of motion in the shoulder and other affected joints. Passive and active range of
motion exercises should begin as soon as the patient's pain has been adequately controlled; these should be followed by regional conditioning of the affected areas.
Strengthening of the rotator cuff muscles and scapular stabilization may be indicated. Passive modalities (eg, heat, cold, transcutaneous electrical nerve stimulation)
may be useful as adjunct pain relievers.
Profound weakness in the shoulder muscles may require the use of a sling; however, unless absolutely necessary, it is generally advised to avoid constantly supporting
the arm in a sling because of the risk of complicating recovery by the development of adhesive capsulitis ("frozen shoulder").
Although neither direct trauma nor localized inflammation due to IM or SQ vaccine injection is thought causative of brachial plexitis, it is empirically recommended that,
if possible, subsequent vaccinations not be given in the affected arm.
30 y/o white male received a vaccination in his left deltoid. He was asymptomatic until about 17 days later he experienced left shoulder pain (2/10) with no decrease in his
range of motion (ROM), no decrease in sensation, no paresthesias, and no weakness. Over the next 10 days the pain progressed to a steady 4/10 pain. Within a few days,
he had difficulty lifting objects, but noted no decrease in the ROM. However, on examination about 1 month post-vaccination, his pain was 6/10, he noted decreased ROM,
and there was left shoulder scapular winging. On exam, there was marked asymmetry with atrophy of left traps, marked drooping of left shoulder, and weak and asymmetric
shoulder shrug on left. He was able to abduct to about 90 degrees, but with scapular stabilization, he was able to abduct to about 130 degrees. He reported occasional
brief paresthesias in his 4th and 5th digits, but otherwise denied lasting paresthesias or numbness. He denied any preceding infectious illness.
His EMG revealed abnormalities of the trapezius muscle, though clinically, serratus anterior is also involved which is innervated by the long thoracic nerve of brachial plexus origin.
MRI of his cervical spine was essentially normal.
He was treated symptomatically with Neurontin tid and Vicodin prn. Three months after onset of symptoms, constant dull pain persisted in left trapezius and scapula regions.
This pain intermittently increased to 3 or 4/10 (about 10 times per day) which lasted from 5 minutes to 3 hours. The patient required narcotics 1-2 nights per week for
difficulty with sleeping due to pain. At 8 months after onset of symptoms, he was about 50 percent better and continues to improve.
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