Brachial Neuritis, also called neuralgic amyotrophy, has two major clinical symptoms: pain and muscle weakness from atrophy. It is a multifocal, immune-mediated inflammatory process that involves the peripheral nerves. Milner reports that up to 80% of patients have a unilateral onset, and 60% involves the dominant side while only 20% had a bilateral extremities onset. Upper and middle trunks are more commonly involved. Most lesions are axonal, however those caused by demyelination usually carry a better prognosis. Motor axons are mainly affected. As a result, nerves that carry mostly motor fibers are affected to a larger degree and more commonly than mixed nerves and pure sensory nerves. Long thoracic, suprascapular, axillary, musculocutaneous nerves, anterior and posterior interosseous nerves are the most commonly affected according to a 2014 study by Ferrante et al. This condition was first reported by Parsonage and Turner in 1948 in a case report, although some records indicate its documentation in the late 19th century.
Brachial neuritis could have a very wide range of etiologies. More common causes that have been reported in the literature include infection, whether bacterial, parasitic or viral; Coxsackie B virus; mumps; variola major and minor; HIV; and parvovirus B19.
Other conditions that predispose patients to develop brachial neuritis are exposure to surgery, anesthesia, hereditary factors, rheumatic diseases such as connective tissue disorders (i.e., Ehlers-Danlos Syndrome), systemic lupus erythematosus, temporal arteritis, and polyarteritis nodosa. Trauma to the shoulder girdle and stressful exercise are other determining factors.
Additional sources include immunizations, including tetanus toxoid and antitoxin, diphtheria, pertussis, tetanus (DPT) vaccine, smallpox, swine flu; pregnancy and childbirth; radiation therapy; lumbar puncture; pneumoencephalogram; radiologic contrast dye administration; and allergy desensitization.
It mostly affects middle-aged males, although it can affect patients of both genders and all age groups. According to a review study by Ferrante et al., 70% of patients were male with an average age of 41.4 years. Milner described the condition in 2016 as rare, with an incidence of 2 to 3 cases per 100 000 per year.
The patient will complain of severe pain that is sudden in onset and involves the lateral aspect of the shoulder as seen in axillary nerve involvement, scapula pain in the suprascapular nerve, the superolateral thoracic wall in long thoracic nerve, antecubital fossa in anterior interosseous nerve, and lateral arm or forearm in musculocutaneous nerve. The acute pain is self-limited and subsides after a few days to weeks. Weakness, changes in reflexes, and sensory deficits will follow. The pain usually is not positional and is worse at night, causing the patient to wake from sleep. The average time between the trigger and the symptoms is 1 to 28 days; however, 66% of patients report the trigger within seven days. According to van Alfen et al., early identification permits medical treatment that may repeal the severity of the clinical course.
It is essential to diagnose brachial neuritis because it can mimic many another diagnoses, such as rotator cuff, cervical cord compression, or nerve entrapment. If brachial neuritis is mistaken for one of these conditions, the patient may undergo unnecessary surgery. Imaging is necessary to diagnose this condition, and an MRI of the shoulder with a special focus on the brachial plexus is needed to rule out musculoskeletal disorders. This must be discussed with the radiologist when ordering the test. Work up includes tests for Epstein Barr virus, varicella zoster, dengue, and hepatitis E. Obtain a detailed history from the patient regarding recent surgery, childbirth, infection, tetanus vaccine, influenza vaccine, and recently prescribed medications such as antivirals, antiepileptic, or botulinum toxins. Nerve conduction/EMG is also crucial in the evaluation of these patients. Electrophysiology studies will show different findings depending on the time of the study and the underlying pathology; for example, if demyelination is the main pathophysiology, then one will see a conduction block, demyelination, or Wallerian degeneration that may occur in varying combinations. Since brachial neuritis is an axonal disorder, nerve conduction velocities and distal latencies are usually normal. A 1996 study by Fibuch et al. showed that 25% of patients had a recent viral illness before the symptoms of brachial neuritis. Ohta et al. found that when emergency situations present in rural areas where there might not be an EMG or MRI machine, proper utilization of knowledge and skills such as gathering accurate history, asking the questions mentioned above, and performing physical examination can lead to the appropriate diagnosis. Newer technology using high-resolution may be helpful as well in the diagnosis of brachial neuritis.
There is no specific treatment for neuralgic amyotrophy; it is a self-limiting condition that resolves on its own. Initially, the severe pain must be treated either with analgesics, such as opioid medications, or neuropathic pain medications, such as tricyclic or antiepileptic agents. Corticosteroids may also help in the acute phase. Strengthening and stretching exercises are very important once the pain is under control. During the acute phase, acupuncture and transcutaneous electrical nerve stimulation (TENS) can be tried. In patients that have superimposed cervical degenerative joint disease where imaging is suggestive of nerve root-level compression, a cervical epidural injection may be helpful to distinguish between pain due to cervical radiculopathy and brachial neuritis. The patient should use the affected extremity as soon as possible and consider a shoulder stabilizer with nonsurgical management. Strengthening exercises are not recommended for completely denervated muscles, and the role of electrical stimulation is controversial but should be considered when the denervated state is for more than 4 months. As a follow-up, EMG could be done of the involved muscles which can show the extent of reinnervation. This bit of information can help one assess which muscles can tolerate a higher level of strengthening and at what time in treatment. For chronic patients, there is evidence that immunotherapy, such as IVIG, may be used but this is still lacking data.
The wide list of possible conditions that brachial neuritis could resemble include diseases of the musculoskeletal systems or other conditions such as cervical root lesion, mononeuritis multiplex, multifocal motor neuropathy, tumors of brachial plexus, transverse myelitis, ALS, herpes zoster, adhesive capsulitis, acute calcific tendinitis, superior sulcus tumor, complex regional pain syndrome, myocardial infarction, and pulmonary embolism.
If pain control, steroids, and an appropriate exercise plan with physical therapy has been prescribed, Ferrante et al reported 89% of patients recovered within 3 years, 75% within 2 years, and 36% within the first year. Recent studies show that many of these patients will continue to have pain and some functional limitation. As seen in the Van Alfen et al. study, persistent pain was experienced by 30% of patients and functional limitations by 66% after a mean of 2.5 years.