Idiopathic Brachial Neuritis

Abstract

Idiopathic brachial neuritis is a well defined clinical condition that most commonly affects young adults, seen usually by primary care physicians, neurologists or orthopaedic surgeons. Its onset is characterized by acute, aching shoulder pain lasting a few days to weeks, followed by progressive shoulder girdle and upper extremity weakness and atrophy, with a slow but progressive recovery of motor function over 6 to 18 months. Its early recognition can help avoid unnecessary and potentially harmful diagnostic and therapeutic interventions, and avoid delays in prescribing appropriate therapies that may be helpful only early in the course of the disease. We present a case of idiopathic brachial neuritis and discuss important aspects of the disease and difficulties in reaching the correct diagnosis.

INTRODUCTION

Idiopathic brachial neuritis (IBN), also known as neuralgic amyotrophy, acute shoulder neuritis, acute brachial neuritis, idiopathic brachial plexus neuropathy or Parsonage-Turner syndrome is a disorder of unknown etiology with asymmetric involvement of the brachial plexus.¹³ It usually affects young adults and presents with acute severe shoulder pain lasting days to weeks followed by painless paresis of the upper extremity with slow but gradual recovery.¹¹ Although in typical cases clinical diagnosis is easy to establish, in atypical presentations or situations where the treating physician is not familiar with this condition, misdiagnosis leading to multiple unnecessary diagnostic and therapeutic interventions can occur. Diagnostic tests such as electromyography and nerve conduction studies (EMG/NCS), magnetic resonance imaging (MRI) of the shoulder, or cerebrospinal fluid (CSF) examination are not required, but can support the diagnosis and rule out other conditions. Good clinical history and examination are key to a correct diagnosis.⁹ We present a complex case of IBN and discuss the more important aspects of the disease.

CASE HISTORY

A 47-year-old right-handed man presented with acute onset left shoulder pain following physical activity related to his job in the construction field. He was evaluated locally and diagnosed with left rotator cuff disease. EMG/NCS were obtained and reportedly showed mild bilateral carpal tunnel syndrome. He underwent surgery for left rotator cuff and left carpal tunnel release. As pain improved, weakness developed in the following weeks, and a repeat EMG/NCS reportedly showed left suprascapular neuropathy, which led to a release procedure on that nerve. In the immediate postoperative period, the pain and weakness worsened, and he also developed numbness in the lateral aspect of the left forearm and hand. The pain was treated with non-steroidal antiinflammatory agents, and an MRI of the cervical spine was obtained which was unremarkable. The pain slowly improved, but the weakness continued to worsen within the following 2-3 weeks. A repeat EMG/NCS was interpreted as probable lateral cord brachial plexopathy, left suprascapular neuropathy, ulnar neuropathy at the elbow and carpal tunnel syndrome. MRI of the left brachial plexus showed nonspecific signal abnormality with T2 hyperintensity interpreted as soft tissue edema from surgery. His past, family and social history were otherwise unremarkable. He was sent to our hospital for second opinion.

On examination by us he was found to have a flaccid, areflexic paresis involving all muscle groups of the left upper extremity, more pronounced in the supra- and infraspinatus, deltoid and biceps, with mild muscle atrophy. Sensory exam showed mild hypesthesia throughout the left upper extremity. The rest of the physical examination was within normal limits. A clinical diagnosis of IBN was established. Over the next year he underwent physical therapy and the paresis has been slowly improving, although it has not completely resolved.

ETIOLOGY AND EPIDEMIOLOGY

The etiology of this condition remains unclear, but an immune attack on the brachial plexus or its branches within the limb triggered by various preceding events (Table 1) has been suggested as a cause,¹⁶ although pathological evidence is scant. ⁷ There is one report of brachial plexus biopsy in patients with IBN showing mononuclear inflammatory infiltrates.¹⁷ Although the great majority of cases of brachial neuritis are sporadic, there is also an autosomal dominant hereditary form, known as hereditary neuralgic amyotrophy (HNA), with some distinct features as discussed below. This disorder has been linked to chromosome 17q24. Patients with HNA suffer recurrent attacks precipitated by the same preceding events as the idiopathic form.⁴

TABLE 1. Preceding Events in IBN.

Infection Vaccination Pregnancy and parturition Trauma at a remote site Surgery Radiation Intravenous heroin use Treatment with interferon

Epidemiologically, IBN presents more commonly in the fourth decade, although it is also seen in children and elderly, and in most series it is more common in men in a proportion of 2:1.⁸ The estimated incidence has been reported to be 1.64/100,000 persons per year, but this figure is probably low due to misdiagnosis and underrecognition of this clinical entity.¹

CLINICAL PRESENTATION

Antecedent events days or weeks prior to onset are reported in 28-83% of cases in different series (Table 1).^7,18 The typical clinical course starts with acute, severe, aching, unilateral shoulder and proximal arm pain lasting from days to a few weeks. When the pain abates, painless shoulder girdle and arm weakness develops, more prominent in the upper plexus muscles including deltoid, supra and infraspinatus, serratus anterior and biceps. Forearm and hand muscles are less frequently involved. Marked atrophy of the involved muscles usually develops, but subsequently there is a slow but steady recovery of motor function over the following 6 to 18 months.¹¹ Usually a longer duration of pain will translate into a longer delay in the recovery phase. The sequence of events described are the classical presentation of IBN, and a good clinical and chronological history should be enough to suspect the diagnosis in the absence of atypical features. A detailed neuromuscular examination will show involvement of two or more nerves, confirming a disorder of the brachial plexus. One highly characteristic feature is differential involvement of different muscles innervated by a single peripheral nerve, a pattern seldom seen with other neuropathic disorders.⁷

The presence of less common clinical features can make the diagnosis difficult. Up to 15 % of patients have been reported to lack the initial painful stage, the symptom that most commonly suggests the diagnosis.⁸ Some patients may have sensory involvement in the form of localized areas of hypoesthesia. Bilateral involvement can be seen in up to 1/3 of patients, although when present is strikingly asymmetric (sometimes one of the involved extremities is asymptomatic, only detected by electrophysiological studies). Single nerve involvement is occasionally seen as the manifestation of IBN, presenting clinically as axillary, suprascapular or long thoracic nerve mononeuropathies, among others. Even less commonly, isolated branches of peripheral nerves can be the only symptom, affecting only individual muscles such as supraspinatus, infraspinatus or flexor pollicis longus.^5,19 Caudal cranial nerves and phrenic nerves may also be affected.^12,14 Very rarely this syndrome can occur in the lumbar area.¹⁵

Pediatric and familial cases differ in some aspects from the more frequent adult-sporadic forms. Children are more likely to have a painless course, have a less favorable recovery, but when they fully recover they do so in a shorter period of time.²¹ Familial cases are more easily identifiable if there is a family history of the disease. It differs from the sporadic form in that there are no gender differences, recurrence is common, cranial nerves are more commonly affected and it may be associated with mild dysmorphic features (Table 2).⁴

TABLE 2. Dysmorphic Features in HNA.

Hypotelorism Epicanthal folds Cleft palate Syndactily or webbing of toes Primitive pinna with folded helix Long narrow face Facial asymmetry

On initial examination, the pain is unaltered by neck or arm movements. Later on, signs of lower motor neuron involvement appear, more pronounced in the upper plexus distribution, with hypotonic, areflexic paresis, and finally signs of denervation such as fasciculations and atrophy. The sensory exam is usually, but not always, intact. All these findings slowly improve during the recovery phase.¹⁰

DIAGNOSIS

The most important element for the correct diagnosis of IBN is clinical suspicion based on a detailed history and examination, with special emphasis in the chronological development of symptoms and signs. Electrophysiological studies are not needed in typical cases, and they usually show denervation of affected and some clinically unaffected muscles.¹⁸ In the acute/subacute stages, MRI of the shoulder shows denervation, best on T2-weighted fast spin-echo images with fat saturation. There is increased signal intensity related to neurogenic edema. During the chronic phase, changes are best seen on T1-weighted spin-echo images, which show loss of muscle bulk and diffuse areas of increased signal intensity within the muscle.^3,6 CSF exam is not routinely obtained and is usually normal, but occasionally shows nonspecific abnormalities, such as mildly elevated proteins and IgG.⁸

When considering the differential diagnosis, four entities are occasionally mistaken for IBN: cervical spine disease, rotator cuff disease, entrapment neuropathies and idiopathic hypertrophic brachial neuritis (IHBN), although a good clinical history and exam should be enough to differentiate these conditions from typical cases of IBN (Table 3).

TABLE 3. Differential Diagnosis of IBN.

Disorder Symptom	Idiopathic Brachial Neuritis*	Cervical Spine Disease	Rotator Cuff Disease	Mononeuropathies	Idiopathic Hypertrophic Brachial Neuropathy
Pain:
-Characteristics	Spontaneous. Burning/aching.	Mechanical, aggravated with neck motion.	Mechanical, aggravated with overhead use. Impingement signs.	Usually painless. If present, pain at entrapment site or neuropathic pain in area innervated by it.	Usually painless. When present, similar to IBN, but milder.
-Onset	Acute.	Usually insidious.	Usually insidious, except posttraumatic injuries.
-Location	Shoulder.	Neck, radiating to shoulder and arm.	Lateral deltoid and deltoid tuberosity.
-Duration	Few days to weeks	Chronic	Chronic
-Chronology	Precedes motor symptoms	Simultaneous with motor symptoms	Simultaneous with motor symptoms
Weakness	Shoulder girdle and arm (more prominent in upper plexus). Slow spontaneous resolution.	Follows root distribution. Needs medical or surgical intervention for improvement.	Shoulder movement muscles. Needs medical or surgical intervention for improvement.	Muscles innervated by single nerve. Resolution and therapy depends on etiology.	Spontaneous resolution but relapses and common residual weakness.

^*In hereditary neuralgic amyotrophy there are multiple recurrent episodes similar to IBN, commonly associated with dysmorphic features

Cervical radiculopathy (CR) can be also characterized by pain and weakness, but with a different pattern. In CR, the pain usually starts in the neck and radiates down the arm, is worsened by neck movements, sometimes begins after physical injury and pain and weakness occur simultaneously. On exam the weakness and hypesthesia follow a root distribution, and imaging studies of the cervical spine or EMG/NCS will show abnormalities in the affected roots.¹⁰

In rotator cuff disease (RCD), more commonly seen with repetitive overhead or throwing movements, the pain has several characteristic differences, and is the main complaint during the full duration of the disease. The pain usually has an insidious onset, localizes to the lateral deltoid or deltoid tuberosity and worsens with motion such as overhead activities. It is also worse at night or even with palpation, does not resolve with the development of weakness and there is decreased range of motion. Signs of impingement are present and, very characteristic of RCD, they resolve after lidocaine injection in the subacromial space. Imaging studies help in the diagnosis of RCD.²⁰

On some occasions, IBN may present as an isolated peripheral nerve lesion, suggesting focal compression, when in fact the pathological process is affecting the brachial plexus and the treatment is non-surgical. Examples are cases of IBN presenting as anterior or posterior interosseous, long thoracic or median nerve syndromes, among others.⁵ The presence of shoulder pain followed by the motor deficits should raise the possibility of IBN, which could be then confirmed by electrodiagnostic studies.

Idiopathic hypertrophic brachial neuritis (IHBN) is a rare, predominantly motor disorder affecting the brachial plexus and more distal upper limb nerve trunks, with progressive weakness in brachial muscles and hypertrophy of the components of the brachial plexus. Its main difference with IBN is its painless course, although some patients may have significant pain. In this disorder, EMG/NCS will show demyelinating features (not seen in IBN), as have been confirmed by histopathological studies, likely representing a localized form of other peripheral demyelinating disorders, such as chronic inflammatory demyelinating polyneuropathy or multifocal motor neuropathy.⁷ Enlargement of the brachial plexus can be seen by MRI, although this is not needed for the diagnosis.

TREATMENT AND PROGNOSIS

The treatment of IBN usually involves a combination of corticosteroids, analgesics, immobilization and physical therapy. The use of corticosteroids is controversial and there are no randomized-controlled trials. However, anecdotal evidence suggests that their use leads to a more rapid resolution of the painful phase of the illness, in particular when used early in its course, although it does not seem to influence the ultimate prognosis. It has been suggested by non-controlled clinical observations that very early treatment with corticosteroids in some cases has resulted in very prompt resolution of the pain, and weakness has not occurred or has been minimal.⁷ We recommend prescribing oral prednisone (1mg/kg/day) for 2 weeks, tapering off over an additional 2 week period, if possible starting 24 to 48 hours after the onset of pain.

The appropriate control of the initial pain is very important, as it can be quite severe and debilitating. Medications used for pain control are narcotics and nonsteroidals, in combinations as needed. Other agents used for control of neuropathic pain such as tricyclics or antiepileptics are not used because of slow onset of action, requiring a few weeks to reach effective pain control. This is an acute onset severe pain of relatively short duration requiring rapid onset-potent analgesics. In addition, immobilization of the extremity during the short painful stage is also recommended. Once the pain is resolved and the weakness is the prominent symptom, physical therapy is usually initiated with prescribed exercises to continue home rehabilitation.

Despite the sometimes dramatic clinical presentation with very severe pain and weakness with denervation, the prognosis is usually good with complete recovery over months in the majority of patients. In a large series, 36% of patients recovered in 1 year, 75 % in two years and 89% in three years.¹⁹ It is very important to inform and educate the patients about the natural history of the disease, and to assure them that, although slow, the recovery is usually very good. Occasionally, there may be residual weakness, or the recovery may be slower taking up to 24 or more months. There are very rare recurrences later in life, but IBN is usually a monophasic illness.² Recurrences are common in the inherited form.

SUMMARY

In summary, IBN is an uncommon condition of probable autoimmune etiology presenting with acute shoulder pain and with a well-defined clinical course. Its diagnosis is easy to establish if the physician is familiar with its clinical manifestations. Detailed history and physical examination may be supported by diagnostic tests as EMG/NCV or MRI of shoulder, which can be useful to exclude other conditions that present with similar symptoms and signs. Management includes a short course of corticosteroids and pain control in the initial stages of the disease, followed by physical therapy. The recovery is usually very good but slow.