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 developing brachial neuritis are exposure to surgery, anesthesia, 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.
The majority of brachial neuritis cases are sporadic, however, there does exist a hereditary form that is autosomal dominant which is called hereditary neuralgic amyotrophy aka HNA. Chromosome 17q24 has been linked to this disease.  The main feature for the hereditary cause is that the affected patient will get recurrent attacks that are caused by the same preceding events as the sporadic form. 
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.
Although the pathophysiology of brachial neuritis is not exactly known, there are 2 theories to explain the mechanism behind the development of this disease. The first one is that viral illnesses, one of the most commonly reported cases, will directly affect the brachial plexus thereby causing the symptoms. The second one is that of an autoimmune cause where the immune system will attack the virus or the antigen affecting the brachial plexus during the process.
For diseases with a vasculitic component such as polyarteritis nodosa, lupus, and temporal arteritis a vascular cause is thought to be responsible for the onset of brachial neuritis.
For pain that is associated with brachial neuritis, ischemia caused by either a mechanical or an inflammatory cause is thought to be related to the onset of sudden extreme pain 
Although the amount of data is sparse, there has been a report of brachial plexus biopsies done in patients with sporadic brachial neuritis which shows mononuclear inflammatory infiltrates.
Nerve biopsies that were done in postsurgical patients with brachial neuritis demonstrated neovascularization, perineural thickening, and focal fiber loss suggesting ischemic changes that points to possible immune pathogenesis 
There are usually three phases in brachial neuritis. In phase 1, the patient will complain of severe pain that is usually unilateral and is described as aching that is sudden in onset and involves the lateral aspect of the shoulder as seen in axillary nerve involvement, scapular 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 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. The acute pain is self-limited and subsides after a few days to weeks. In general, the longer the pain lasts the longer it will take for the patient to recover. In a typical course, after the pain resolves, patients will enter phase 2 of the disease and will start to develop weakness that is painless such as arm and shoulder girdle weakness. The forearm and hands can also be involved but are much less common. Atrophy of the muscles also starts to occur but there is usually a slow steady recovery of muscle function afterward following 6 to 18 months known as phase 3 of the disease.
On physical examination, typically 2 or more nerves will be involved. One unique characteristic that can differentiate brachial plexus neuritis from other conditions is that in brachial neuritis there is differential involvement of the different muscles that are innervated by the same peripheral nerve (pathy paresis). Lower motor neuron signs can be appreciated later on in the disease course on physical exam (hypotonia, areflexia, atrophy, and fasciculations) mainly in the upper brachial plexus (C5,6,7). For weakness that occurs after the acute pain phase, shoulder abduction and external rotation will be decreased signifying involvement of the deltoids, supraspinatus, and infraspinatus muscles. When the long thoracic nerve is involved you will get medial scapular winging due to involvement of the serratus anterior muscle. Sensory changes can also be present in about 78% of patients consisting of paresthesias and hypoesthesia over the lateral arm, deltoids, and radial forearm. Patients may not notice sensory changes due to severe severe pain.
It is essential to diagnose brachial neuritis because it can mimic many other 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. Although obtaining a good and thorough history and physical will usually be enough to diagnose brachial neuritis, the use of imaging is helpful to support the diagnose of this condition as well as ruling out other conditions. The use of an MRI of the shoulder with a special focus on the brachial plexus should be used to rule out musculoskeletal disorders. This must be communicated to the radiologist when ordering the test. For acute stages, the MRI on T2 will show signal hyperintensity(suggesting edema) within the affected muscles. For chronic stages, the MRI on T1 will show intramuscular signal intensity(signifying fatty infiltration) and atrophy of the affected muscles.
Other workups such as CBC and ESR will usually be normal while other labs such as LFTs and ANA will be abnormal but are inconclusive. Other diagnostic modalities such as plain radiographs and CSF analysis will usually be normal. Further workup includes tests for Epstein Barr virus, Varicella-zoster, dengue, and Hepatitis E. Obtaining 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 is important as well.
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 while there will be reduced amplitudes. In early findings such as 3 to 4 weeks after symptoms, the EMG will usually show acute denervation with fibrillation potentials as well as positive sharp waves for nerve roots and peripheral nerves. In later stages (3-4 months after symptoms) the EMG will show chronic denervation and polyphasic motor unit potentials with early reinnervation. 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 should be treated with analgesics, such as opioid medications and/or NSAIDs. Although neuropathic pain medications, such as tricyclic or antiepileptic agents would initially make sense, this is not recommended due to the fact that these medications have a slow onset . Since the acute pain phase is typically short in duration, a relatively fast-acting analgesic is needed. Corticosteroids may also help in the acute phase and have been shown to lead to a faster resolution of the acute pain but do not overall influence the overall prognosis of brachial neuritis. Immobilization of the affected extremity is also important during the acute pain phase but afterwards, 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, amyotrophic lateral sclerosis, Herpes zoster, adhesive capsulitis, acute calcific tendinitis, superior sulcus tumor, complex regional pain syndrome, myocardial infarction, and pulmonary embolism.
If pain control, corticosteroids, and an appropriate exercise plan with physical therapy has been prescribed, Ferrante et al. reported 89% of patients recovered within three years, 75% within two years, and 36% within the first year. Recent studies show that many of these patients will continue to have pain and some functional limitation, however, full recovery of strength is possible and can take up to 8 years. 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. 
Some factors associated with poorer prognosis are female gender, persistent pain as well as lack of motor recovery by three months, lower trunk involvement (upper trunk involvement has better prognosis), and hereditary cases (idiopathic cases have rare recurrence rate whereas hereditary cases have much more common recurrence rates).
Although the majority of patients do recover from brachial neuritis, complications are not uncommon. Because of the atrophy and weakness that is associated, patients can have the positions of their joints shifted slightly such as in the shoulders, wrist, and hands. Because of this, the risk of subluxation or impingement is higher. Adhesive capsulitis of the shoulder could also result which will cause pain and a limited range of motion to the shoulders. Patients with persistent residual pain and weakness can also have trouble doing everyday tasks such as reaching or lifting objects or doing repetitive tasks with their shoulders and/or arms. Patients who have repeat episodes of brachial neuritis, such as those who have the hereditary form, are also at a higher risk of getting these complications.
For many patients, their symptoms will start to resolve in a few months but it is not uncommon for it to take much longer. Patience is key. The best thing that one can do is to adequately control their pain with medications prescribed by their doctors. After their pain resolves, physical therapy will be crucial in addressing the weakness that will typically present after the pain subsides. Although there is no guarantee in preventing brachial neuritis, the best advice is to prevent shoulder or arm injuries since that can potentially predispose them to the condition. Otherwise, there is not much else that one can do to prevent the condition.
As with other types of peripheral neuropathies, avoiding cigarettes and alcohol, eating a healthy diet along with regular exercises can certainly help with this condition.
Not surprisingly, this condition can cause a lot of anxiety and emotional stress. Patients are encouraged to participate in relaxation techniques like yoga which can reduce their stress levels. EMG followup studies can also be done since these tests can show early signs of recovery before clinical signs of recovery thereby helping to relieve patient's anxieties.
An interprofessional team manages brachial neuritis. The diagnosis is often difficult, and delay in treatment is common. Besides the orthopedic and hand surgeon, other team members may include a neurologist, physical therapist, pharmacist, pain specialist, and specialty trained nurses in neurology and pain management. There are a variety of treatments for brachial neuritis, but physical therapy is the first-line treatment. Pharmacists should evaluate medications prescribed, drug-drug interactions, and patient compliance and communicate with the team. Specialty trained nurses assist with the education of the patient and their family and report issues to the team.
The outcomes of patients with brachial neuritis are guarded. No treatment works reliably, and relapse is common. The disorder can affect the quality of life. Hence a mental health consultation should be obtained. 
|||Parsonage-Turner Syndrome: Clinical and Epidemiological Features From a Hand Surgeon's Perspective., Milner CS,Kannan K,Iyer VG,Thirkannad SM,, Hand (New York, N.Y.), 2016 Jun [PubMed PMID: 27390568]|
|||Parsonage-turner syndrome., Feinberg JH,Radecki J,, HSS journal : the musculoskeletal journal of Hospital for Special Surgery, 2010 Sep [PubMed PMID: 21886536]|
|||Gonzalez-Alegre P,Recober A,Kelkar P, Idiopathic brachial neuritis. The Iowa orthopaedic journal. 2002; [PubMed PMID: 12180618]|
|||Brachial plexitis or neuritis? MRI features of lesion distribution in Parsonage-Turner syndrome., Sneag DB,Rancy SK,Wolfe SW,Lee SC,Kalia V,Lee SK,Feinberg JH,, Muscle & nerve, 2018 Feb 20 [PubMed PMID: 29461642]|
|||Fibuch EE,Mertz J,Geller B, Postoperative onset of idiopathic brachial neuritis. Anesthesiology. 1996 Feb [PubMed PMID: 8602681]|
|||High-resolution ultrasound in patients with Wartenberg's migrant sensory neuritis, a case-control study., Herraets IJT,Goedee HS,Telleman JA,van Asseldonk JH,Visser LH,van der Pol WL,van den Berg LH,, Clinical neurophysiology : official journal of the International Federation of Clinical Neurophysiology, 2018 Jan [PubMed PMID: 29202391]|
|||The electrodiagnostic natural history of parsonage-turner syndrome., Feinberg JH,Nguyen ET,Boachie-Adjei K,Gribbin C,Lee SK,Daluiski A,Wolfe SW,, Muscle & nerve, 2017 Oct [PubMed PMID: 28044362]|
|||Morishima R,Nagaoka U,Nagao M,Isozaki E, Chronic Brachial Plexus Neuritis That Developed into Typical Neuralgic Amyotrophy and Positively Responded to Immunotherapy. Internal medicine (Tokyo, Japan). 2018 Apr 1 [PubMed PMID: 29269655]|
|||van Alfen N,van Engelen BG, The clinical spectrum of neuralgic amyotrophy in 246 cases. Brain : a journal of neurology. 2006 Feb [PubMed PMID: 16371410]|
|||Calvo-Lobo C,Unda-Solano F,López-López D,Sanz-Corbalán I,Romero-Morales C,Palomo-López P,Seco-Calvo J,Rodríguez-Sanz D, Is pharmacologic treatment better than neural mobilization for cervicobrachial pain? A randomized clinical trial. International journal of medical sciences. 2018; [PubMed PMID: 29559834]|
|||Clarke CJ,Torrance E,McIntosh J,Funk L, Neuralgic amyotrophy is not the most common neurologic disorder of the shoulder: a 78-month prospective study of 60 neurologic shoulder patients in a specialist shoulder clinic. Journal of shoulder and elbow surgery. 2016 Dec; [PubMed PMID: 27282731]|