A Man in the “Barrel”

A 37-year-old man presented with a 3-week history of difficulty with his right handgrip. He denied numbness, paresthesias, or leg weakness. He had some mild chronic neck pain, but his MRI of the spine was normal. Family history and past medical and social histories were noncontributory.

Mentation and cranial nerve examination were normal. There was atrophy of the right first dorsal interosseous muscle with weakness of the hand intrinsic muscles, but other muscles were normal. There were no fasciculations. Sensory examination and reflexes and the rest of the examination were normal.

What is the Differential Diagnosis?

The atrophy and weakness in the hand muscles suggest a C8 radiculopathy or a lower trunk or medial cord plexus lesion. The lack of significant pain or sensory abnormalities is against these diagnoses. The lack of pain and normal MRI also ruled out other spinal diseases.

Other possibilities include a motor neuron disease and multifocal motor neuropathy (MMN), but in this disease, there is usually weakness with little atrophy. A mononeuritis multiplex could be considered, but it is hard to make this diagnosis when only one level is affected and, particularly, with the lack of sensory findings. Adult-onset myopathies with hand wasting such as debrancher enzyme deficiency and Welander muscular dystrophy are less likely possibilities, as they are usually symmetrical at onset.

An EMG Test Was Performed

Motor Nerve Studies

Nerve and Site	Latency (ms)	Amplitude (mV)	Conduction Velocity (m/s)
Median Nerve R.	Normal ≤ 4.2	Normal ≥ 6	Normal ≥ 50
Wrist	5.5	2	–
Elbow	10.3	2	51

Ulnar Nerve R.	Normal ≤ 3.6	Normal ≥ 8	Normal ≥ 50
Wrist	3.0	15	–
Below elbow	6.8	13	55
Above elbow	8.6	11	66
Axilla	10.8	11	55

Median Nerve L.	Normal ≤ 4.2	Normal ≥ 6	Normal ≥ 50
Wrist	3.7	15	–
Elbow	7.5	13	61

Nerve and Site	Latency (ms)	Amplitude (mV)	Conduction Velocity (m/s)
Peroneal Nerve R.	Normal ≤ 5.7	Normal ≥ 3	Normal ≥ 40
Ankle	4.2	4	–
Fibular head	10.3	3	47
Knee	12.1	3	56

F-Wave and Tibial H-Reflex Studies

Nerve	Latency (ms)	Normal Latency ≤ (ms)
Median nerve R.	31.0	30
Ulnar nerve R.	28.6	30
Median nerve L.	27.7	30
Peroneal nerve R.	47.8	54
H-reflex R.	30.3	34

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 R.	2.8	2.6	3.3	3.1	31	20	46	50
Ulnar nerve R.	2.3	2.6	2.8	3.1	16	13	52	50
Median nerve L.	2.9	2.6	3.4	3.1	31	20	45	50
Sural nerve R.	3.1	3.5	3.6	4.0	37	11	45	40

EMG Data

Muscle	Insrt Activity	Fibs	Pos Waves	Fasc	Amp	Dur	Poly	Pattern
Tongue	Norm	None	None	None	Norm	Norm	None	Full
Thoracic paraspinals R.	Norm	None	None	None	Norm	None	None	Full
Supraspinatus R.	Norm	None	None	None	Norm	Norm	None	Full
Deltoid R.	CRD	None	1+	None	Norm	Norm	None	Full
Biceps brachii R.	Inc	None	None	Few	Lg	Inc	None	Full
Flexor carpi radialis R.	Inc	2+	2+	None	Lg	Inc	None	Full
Flexor carpi ulnaris R.	Inc	2+	2+	Few	Lg	Inc	None	Red
Triceps R.	Inc	None	None	Few	Lg	Inc	None	Red
Extensor digitorum comm. R.	Inc	2+	2+	None	Norm	Norm	None	Full
Sternocleidomastoid R.	Norm	None	None	None	Norm	Norm	None	Full
Abductor poll. brevis R.	Inc	None	2+	None	Lg	Inc	None	Red
First dorsal interosseous R.	Inc	2+	2+	None	Lg	Inc	None	Red
Vastus lateralis R.	Norm	None	None	None	Lg	Inc	None	Red
Tibialis anterior R.	Inc	None	1+	None	Lg	Inc	None	Full
Peroneus longus R.	Inc	None	1+	None	Norm	Norm	None	Full
Gastrocnemius R.	Inc	None	1+	None	Norm	Norm	None	Full
Deltoid L.	Norm	None	None	None	Norm	Norm	None	Full
Biceps brachii L.	Norm	None	None	None	Lg	Inc	None	Full
Flexor carpi ulnaris L.	Norm	None	None	None	Norm	Norm	None	Full
Extensor digitorum comm. L.	Norm	None	None	None	Norm	Norm	None	Full
Abductor poll. brevis L.	Inc	None	1+	None	Lg	Inc	None	Red
First dorsal interosseous L.	Inc	None	1+	None	Lg	Inc	None	Red