A 33-year-old man came in with left arm pain and numbness in the hand for 5 weeks. He practiced karate. His past medical history was negative.
There was weakness without atrophy of the thumb flexion at the distal phalanx and mild weakness of the first two finger flexors. Pain sensation was decreased in the first three digits and median palmar area of the hand and thumb. There was mild tenderness of the forearm. A Phalen test was negative. No Tinel’s sign was elicited at the elbow, arm, or wrist. The rest of the neurologic examination was normal.
What is the Differential Diagnosis?
This patient developed symptoms suggestive of a median neuropathy. The differential diagnosis was a plexopathy or radiculopathy, but because of the focal pain in the forearm, a proximal median neuropathy in this area was a strong consideration. A carpal tunnel syndrome (CTS) seemed less likely.
The sensory abnormality in the hands also included the palmar area of the thumb which should not be affected in CTS, as the sensory branch to this area comes from above the flexor retinaculum.
This patient practiced karate and had frequent pronation movement of the forearm while playing the sport. It was thought that he had damage to the median nerve as it passes to the pronator teres muscle. Other possible causes include masses, fibrous bands, or hypertrophy of the teres muscle.
An EMG Test was Performed
Motor Nerve Studies
Nerve and Site
Latency (ms)
Amplitude (mV)
Conduction Velocity (m/s)
Median Nerve L.
Normal ≤ 4.2
Normal ≥ 6
Normal ≥ 50
Wrist
3.9
12
–
Elbow
8.5
8
58
Above elbow
10.5
8
51
Ulnar Nerve L.
Normal ≤ 3.6
Normal ≥ 8
Normal ≥50
Wrist
2.9
19
–
Below elbow
6.4
18
58
Above elbow
8.3
18
63
Axilla
11.2
18
53
Erb’s point
14.5
16
63
Nerve and Site
Latency (ms)
Amplitude (mV)
Conduction Velocity (m/s)
Median Nerve R.
Normal ≤ 4.2
Normal ≥ 6
Normal ≥ 50
Wrist
3.6
11
–
Elbow
8.0
11
55
Above elbow
10.2
11
55
Ulnar Nerve R.
Normal ≤ 3.6
Normal ≥ 8
Normal ≥ 50
Wrist
2.9
18
–
Below elbow
6.7
18
57
F-Wave Studies
Nerve
Latency (ms)
Normal Latency ≤ (ms)
Median nerve L.
29.7
30
Ulnar nerve L.
29.0
30
Median nerve R.
29.3
30
Ulnar nerve R.
28.6
30
Sensory Nerve Studies
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 L.
2.3
2.6
2.8
3.1
16
20
57
50
Ulnar nerve L.
2.3
2.6
3.0
3.1
28
13
52
50
Median nerve R.
2.3
2.6
2.8
3.1
36
20
57
50
Ulnar nerve R.
2.3
2.6
2.8
3.1
37
13
52
50
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