A Diabetic Man With Shoulder Pain and Weakness

A 42-year-old, type 2 diabetic man on oral antidiabetics developed a sudden onset of pain and weakness in the left shoulder. The pain worsened with movement. The patient states that he woke up with these symptoms and went to the ER where he had X-rays of the neck that were normal. He was treated with common analgesics and was referred to us by his internist after 3 weeks.

He stated that before the onset of symptoms he was carrying some boxes but he did not carry excessive weight.

Physical examination revealed normal mentation and cranial nerves. There was mild tenderness to palpation of the left shoulder over the scapular area. The shoulder joint was not tender. The patient also had weakness of external rotation and abduction, particularly in the initial 15 degrees of movement of the arm. The deltoid muscle and other arm muscles were normal. There was mild flattening of the infraspinatus muscle. Reflexes were equal and symmetric, except for trace at the ankles. There were no Babinski signs. There was decreased vibration sense at the toes and pinprick was normal. Upper extremity sensory examination was normal.

What is the Differential Diagnosis?

The shoulder pain could suggest an orthopedic process, such as rotator cuff syndrome, but the pain on examination was not in the rotator area but in the scapulae. The weakness was out of proportion to the pain, making this diagnosis unlikely. The possibility of brachial neuritis needed to be considered, but the process seemed to involve only the spinati muscles. The sparing of deltoids, serratus, and other muscles in the arm argues against a diagnosis of radiculopathy or a plexopathy.

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	3.8	11	–
Elbow	8.7	11	50

Ulnar Nerve L.	Normal ≤ 3.6	Normal ≥ 8	Normal ≥ 50
Wrist	3.0	17	–
Below elbow	7.5	15	51
Above elbow	9.5	15	52

Nerve and Site	Latency (ms)	Amplitude (mV)	Conduction Velocity (m/s)
Peroneal Nerve L.	Normal ≤ 5.7	Normal ≥ 3	Normal ≥ 40
Ankle	4.6	2	–
Fibular head	13.1	1	38
Knee	14.6	1	45
Suprascapular Nerve L . ^a
Supraspinatus L.	4.9	1	–
Infraspinatus L.	4.0	2	–
Suprascapular Nerve R . ^a
Supraspinatus R.	3.1	5	–
Infraspinatus R.	3.0	4	–