Brachial plexitis is a condition characterized by acute onset of shoulder pain followed by weakness and/or sensory loss of the shoulder and/or upper extremity. Dreschfeld first described it in 1887. Multiple reports further described the condition. The most important one out of these was the report of 136 patients by Parsonage and Turner in 1948. It was this report that strongly characterized the clinical history of the condition. Since then, the condition has been known by many different names such as Parsonage-Turner syndrome, neuralgic amyotrophy, acute brachial neuropathy, acute brachial plexitis, idiopathic brachial plexopathy, idiopathic brachial neuritis, paralytic brachial neuritis, and brachial radiculitis, among others.
There are wo different forms of brachial plexitis. One is an idiopathic form, and the other, a hereditary form. The etiology of the idiopathic form is unknown. The idiopathic form is associated with recent viral infection, specifically upper respiratory tract infection, as well as recent vaccination. Recent infection has been associated to precede the development of the disease in 25% to 55% of patients, while recent vaccination has been associated with 15% of patients. Infectious causes include smallpox, influenza, coxsackievirus, parvovirus B19, cytomegalovirus, HIV, typhoid fever, and Borrelia burgdorferi. Other causes include strenuous exercise, pregnancy, and post-surgical plexopathy. The hereditary form is an autosomal dominant recurrent brachial plexitis. Researchers think it is due to a mutation causing a deficiency in proteins from the septin family.
The incidence of brachial plexitis is estimated to be approximately 1.64 cases per 100,000 person-years. Males are more commonly affected than females. Multiple males to female ratios have been reported, ranging from 2:1 to 11.5:1. Cases have been reported in patients three months to 75 years old. The peak age for onset of the disease is during the third and seventh decades.
The exact pathophysiologic mechanism is unknown, but there are some possible explanations for the different forms. One study suggested that patients with the disease have increased the immunologic activity of lymphocytes when exposed to brachial plexus nerve extracts versus sacral plexus nerve extracts. Another study suggested that in patients with early disease, there is an increase in antibodies to peripheral nerve myelin. These findings, along with the association of disease occurrence with recent infection or vaccination, serve as a basis for the immunologic mechanism of the disease. The hereditary form is an autosomal dominant brachial plexitis due to various types of mutations in the Septin 9 gene, chromosome 17q25. Septin 9 is a guanosine 5' triphosphate (GTP)-binding protein highly expressed in glial cells. It is involved in cytoskeleton regulation and function. The hereditary form of brachial plexitis is associated with recurrent disease.
As previously stated, patients may have a history of viral infection or recent vaccination. The most common initial symptom is acute onset of intense pain. This pain occurs in 95% of patients. The pain may involve:
It is a constant pain with variable quality, often exacerbated by movement of the shoulder or arm. It can be somewhat relieved by elbow flexion and shoulder adduction (minimizing shoulder and arm movement). On average, the pain may last from two to three hours to more than eight weeks.
Weakness ensues after the acute onset of pain. The onset of the weakness is sudden in 80% of patients. It can coincide with the pain or in a delayed fashion. Seventy percent of patients report the weakness within two weeks of the onset of pain. Fifty percent of patients have isolated shoulder girdle weakness, while only 10% have weakness localized to the distribution of a single peripheral nerve. The most commonly affected muscles are the spinati, serratus anterior, deltoid, biceps, and triceps. Despite this, cases of unilateral or bilateral phrenic nerve neuropathy have been described, resulting in diaphragmatic paralysis. Sixty-six percent of cases are unilateral, and 34% of cases are bilateral. Of the cases that are unilateral, 54% involve the right side. No statistically significant relationship has been described between unilaterality of the disease and the patient's dominant side. A winged scapula may be observed in 20% of cases.
Sensory deficits have been described in 78% of cases. Paresthesias have been described in 35% of cases. Isolated paresthesias or a combination of paresthesia and hypoesthesia are the most common sensory complaints. They usually involve the deltoid and lateral aspect of the upper arm and the radial aspect of the forearm.
Patients also reported other, less common symptoms such as autonomic dysfunction, craniofacial dysmorphisms, and unusual skin folds.
No laboratory test may help suggest the diagnosis of brachial plexitis. However, MRI of the shoulder, electromyography, and nerve conduction studies may provide important clues toward the diagnosis.
In the acute phase of the disease, MRI of the shoulder can reveal diffuse T2 signal hyperintensities as a consequence of the edema secondary to nerve demyelination. In the subacute or chronic phases, the T2 signal changes persist, and new T1 linear hyperintensities may develop, corresponding with fatty infiltration of the affected muscles. MRI of the brachial plexus is not sufficiently sensitive for appreciating changes related to the disease, but magnetic resonance neurography of the brachial plexus may show thickening and hyperintensity in the acute phase. This hyperintensity may persist into the chronic phase.
Electromyography (EMG) is the best study for evaluation of demyelination of the brachial plexitis. It has to be performed three weeks after the onset of symptoms to show any significant findings. EMG may show positive sharp waves and fibrillation potentials consistent with acute denervation. If performed late into the disease (three to four months), it may show chronic denervation and early reinnervation. Nerve conduction studies are usually normal but may show proximal conduction blocks.
It is important to note that brachial plexitis is a diagnosis of exclusion, which means practitioners have to rule out other possible pathologies before making the diagnosis. Most of these tests are good at ruling in or out other diagnoses but not at confirming a diagnosis of brachial plexitis.
The treatment of brachial plexitis is conservative, based on analgesia and physiotherapeutic rehabilitation. Analgesia is best achieved with non-steroidal anti-inflammatory drugs (NSAID). Some studies have suggested that corticosteroid use early in the disease may reduce pain and weakness recovery time, but their clinical significance is still to be proven. Physiotherapeutic rehabilitation, which may include kinesiotherapy, transcutaneous electrical nerve stimulation, deep dermal therapy, cryotherapy and/or functional electric stimulation, has been shown to be effective in reducing pain and weakness, as well as in regaining muscle trophism and functional status.
The differential diagnosis of brachial plexitis includes the following:
Sixty percent of upper plexus lesions may recover in less than one year, while lower plexus lesions may take between one and a half to three years. Estimated rate of recovery is 36%, 75% and 89% within one, two, and three years, respectively. Idiopathic reoccurrence is estimated to be 5%, although other figures have been proposed.