A 35-year-old woman presented with a 3-week history of right shoulder pain with numbness in the forearm and difficulty raising her arm. She had an upper respiratory infection 2 weeks before presentation.
Past medical history was unremarkable. She drank alcohol occasionally but did not smoke. She denied using illegal drugs.
Examination revealed winging of the right scapula toward the middle when the arm was extended forward, indicating weakness of the serratus ( Fig. 11-1 ) rather than the trapezius muscle. ( Fig. 11-2 demonstrates another patient who had spinal accessory neuropathy and trapezius weakness.) There was mild weakness of the right deltoid and only flexion of the distal phalanx of the first two fingers of the right hand. Also, the patient had difficulty opposing the thumb to the fifth digit. She had patchy decreased pain sensation in the shoulder. Reflexes were 2+ throughout, except for the right biceps and brachioradialis reflexes which were 1+. The rest of the examination was normal.
What is the Clinical Diagnosis?
The arm pain with weakness in muscles innervated by the upper trunk of the brachial plexus and C5–C6 roots suggested a radiculopathy or an upper trunk brachial plexopathy. She, however, also had weakness in muscles not innervated by the C5–C6 roots and the upper trunk of the brachial plexus. The lack of neck pain is somewhat against the diagnosis of radiculopathy.
The acute presentation with pain and weakness of muscles involved by several nerves, preceded by a recent viral infection, is in favor of this being an acute brachial neuritis (BN).
Other possibilities to consider include a hematoma or a tumor in the upper plexus or roots, but as discussed earlier, she also had weakness of the flexors of the fingers, particularly the thumb and index finger, which are not innervated by the C5–C6 roots or the upper trunk. These muscles, the flexor digitorum profundus and flexor pollicis longus, are innervated by the median nerve, particularly through its anterior interosseous branch, from axons coming off the C7 and C8 roots and middle and lower trunks of the plexus.
An Emg Test was Performed
| Nerve and Site | Latency (ms) | Amplitude (mV) | Conduction Velocity (m/s) |
|---|---|---|---|
| Median Nerve R. | Normal ≤ 4.2 | Normal ≥ 6 | Normal ≥ 50 |
| Wrist | 3.8 | 16 | – |
| Elbow | 7.8 | 16 | 56 |
| Ulnar Nerve R. | Normal ≤ 3.6 | Normal ≥ 8 | Normal ≥ 50 |
|---|---|---|---|
| Wrist | 3.3 | 12 | – |
| Below elbow | 6.8 | 12 | 60 |
| Above elbow | 8.9 | 12 | 60 |
| Nerve and Site | Latency (ms) | Amplitude (mV) | Conduction Velocity (m/s) |
|---|---|---|---|
| Axillary nerve R. | 6.2 | 1 | – |
| Axillary nerve L. | 2.9 | 5 | – |
| Nerve | Latency (ms) | Normal Latency ≤ (ms) |
|---|---|---|
| Median nerve R. | 26.8 | 30 |
| Ulnar nerve R. | 26.4 | 30 |
| Nerve | Onset Latency (ms) | Normal Onset Latency ≤ (ms) | Peak Latency (ms) | Normal Peak Latency ≤ (ms) | Amp (μV) | Normal Amp ≥ (μV) | Conduction Velocity (m/s) | Normal Conduction Velocity ≥ (m/s) |
|---|---|---|---|---|---|---|---|---|
| Median nerve R. | 2.1 | 2.6 | 2.6 | 3.1 | 25 | 20 | 62 | 50 |
| Ulnar nerve R. | 1.9 | 2.6 | 2.4 | 3.1 | 20 | 13 | 63 | 50 |
| Lat. cut. nerve R. | 1.8 | b | 2.3 | 2.6 | 11 | 12 | b | b |
| Lat. cut. nerve L. | 1.6 | b | 2.2 | 2.6 | 19 | 12 | b | b |
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