Sudden, Severe Upper Limb Pain and Weakness in a Sleepless Man

Olusegun John Oluwole, MBBS

Disclosures

December 14, 2020

After a normal cervical spine MRI, a shoulder MRI was ordered. The results were unremarkable, as shown in Figures 3 and 4 below.

Figure 3.

Figure 4.

The patient was referred for nerve conduction studies and electromyography (EMG). These tests revealed an axonal lesion involving the upper trunk of the left brachial plexus, in addition to bilateral demyelinating median neuropathy at the wrist and lower limb distal sensory axonal polyneuropathy. Nerve conduction and EMG findings are shown below in Tables 1 and 2, respectively.

Table 1. Results of Nerve Conduction Studies

Nerve Onset latency Peak latency Amplitude Conduction velocity
Left median sensory 4.0 ms 4.6 ms 14 µV 39 m/s
Left median motor 6.0 ms -

Wrist: 6.2 mV

Elbow: 6.0 mV

Axilla: 5.6 mV

 

 

55.0 m/s

 

50.0 m/s

Left axillary 5.2 ms - 1 mV -
Left infraspinatus 3.5 ms - 1.8 mV -
Left musculocutaneous 5.0 ms - 6.5 mV -
Right sural nerve 3.2 ms 4.1 ms 6.0 µV 42 m/s
Right median sensory 3.9 ms 4.4 ms 12 µV 36 m/s
Right median motor 5.8 ms -

Wrist: 5.9 mV

Elbow: 5.2 mV

Axilla: 5.1 mV

 

 

58.0 m/s

 

55.0 m/s

Right axillary 4.8 ms - 6 mV -
Right infraspinatus 3.5 ms - 5.3 mV -
Right musculocutaneous 5.2 ms - 5.9 mV -
Right sural nerve 3.0 ms 3.9 ms 6.6 µV 40 m/s

Table 2. Results of Electromyography

Muscle Insertional Activity Spontaneous Activity Fasciculations Polyphasic Potentials Recruitment
Infraspinatus (left) Increased Fibrillations and PSWs Present Increased Discrete
Deltoid (left) Increased Fibrillations Absent Normal Discrete
Serratus anterior (left) Increased Fibrillations and PSWs Absent Increased Reduced
Biceps (left) Normal None Absent Normal Full
Triceps (left) Normal None Absent Normal Full

PSW = positive sharp wave

Brachial neuritis, or Parsonage-Turner syndrome, is a rare inflammatory disorder of the brachial plexus. Its incidence is reported to be 2-3 cases per 100,000 population.[7] It is most commonly encountered in middle-aged men, although cases have been reported in virtually all age groups, including children.[7,8] The clinical manifestation is usually unilateral but can occasionally be bilateral, in which case it shows striking asymmetry between the two sides. Extra-brachial and cranial nerve involvement has also been reported, albeit rarely.[7]

The disease is most often idiopathic, but cases have occurred following vaccinations, infections, trauma at remote sites, and surgery.[3] In cases associated with infections, it is unclear whether what underlies the disease is a direct infection of the brachial plexus or a secondary autoimmune reaction to the infectious agent. Microvascular injury to brachial plexus elements has also been postulated as a plausible underlying mechanism.[8] Regardless of what the mechanism may be, persons with brachial neuritis seem to have a genetic predisposition that requires a trigger to initiate the autoimmune attack on the brachial plexus.[9]

The onset is usually heralded by intense pain around the shoulder girdle and upper arm. The pain is typically worse at night and may be so intense as to awaken the patient. The location of the pain often corresponds to the course of the affected nerves. Pain in the lateral aspect of the shoulder occurs with axillary nerve involvement, scapular pain with suprascapular nerve involvement, superolateral thoracic wall pain with long thoracic nerve involvement, and lateral arm and forearm pain with musculocutaneous nerve involvement.[8]

The pain starts to resolve after few weeks, and this resolution is followed by rapidly progressive shoulder girdle muscle weakness and wasting. Sensory disturbances may be associated with the weakness, commonly manifesting as sensory loss or allodynia over the deltoid area with or without extension to the lateral forearm. Muscle wasting and weakness may continue to progress for several weeks, but recovery usually begins within 6 months. Complete or near-complete recovery is expected at 18 months.

Careful neuromuscular examination typically reveals the involvement of at least two nerves, a feature that helps localize the lesion to the brachial plexus. One intriguing feature of brachial neuritis is that different muscles are affected within the same peripheral nerve distribution.[8] Although the involvement of at least two peripheral nerves is usual, atypical cases have been reported in which a single peripheral nerve is affected in isolation.[3] The most commonly affected nerves in brachial neuritis include the long thoracic, suprascapular, axillary, musculocutaneous, and anterior and posterior interosseous nerves.[8] Brachial neuritis typically follows a monophasic course, although recurrences have been reported in the hereditary form of the disease.

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