Differential Diagnosis/ Radiculopathy
The differential first involves looking for a pinched nerve in the neck (cervical radiculopathy or nerve compression). In cervical nerve compression, the pain, numbness and weakness are only involved with one nerve root (possibly two in uncommon cases). An examination will also note nerve pain radiating into the shoulder with neck extension (bending the head backwards-the Spurling’s test) as the pinched nerve will become more compressed with neck extension.
In Parsonage Turner Syndrome, the muscles that are involved are always in a scattered distribution with no rhyme or reason and are not specific for one spinal nerve. That is, there is no classic pattern of involvement like that of a compressed spinal nerve. Motor strength testing will find multiple nerve involvements. Bending the head backwards should not increase the pain into the arm.
The EMG test (nerve conduction test) if performed at least three weeks after onset of symptoms will be helpful in differentiating the two disorders. The three week period is necessary to allow changes to the muscles that make the EMG test responsive. If the test is performed before three weeks, it may be negative (won’t show nerve injury).
The reason this test can differentiate the two disorders is anatomy. The spinal nerve is one complete nerve until it splits into two branches right after it exits the foramen (the exit hole in the vertebrae). The two branches become the anterior primary ramus and the posterior primary ramus.
The anterior primary ramus is the much thicker main branch that travels into the shoulder and joins the brachial plexus. This anterior branch is responsible for function of all of the shoulder and arm muscles. The posterior primary ramus is a much smaller branch that is only responsible for the very small muscles of the back of the neck.
Cervical radiculopathy (nerve compression in the neck) injures the nerve before it exits the foramen (the exit hole in the vertebrae). Since the nerve is affected before it splits, both the anterior and posterior primary ramus of the nerve will be injured.
Parsonage Turner Syndrome involves the nerve after it has exited and split into two. This means that in Parsonage Turner Syndrome, the anterior primary ramus is involved but the posterior primary ramus is not involved.
If the EMG test picks up neurogenic changes in the small muscles of the back of the neck, this is a pinched nerve in the neck (cervical radiculopathy). If these small back-of the-neck muscles are normal (not involved), this is most likely Parsonage Turner Syndrome.
Other Differential Diagnoses
Shingles is the reactivation of the chickenpox virus (varicella) that has lain dormant in one nerve root for years. The pain from shingles is very similar to the initial pain of Parsonage Turner Syndrome. Shingles however will develop vesicles (small fluid-filled pimple-like lesions) one to two days after pain onset. Also careful evaluation will reveal that the pain in Shingles is from only one nerve whereas Parsonage Turner Syndrome pain will be from multiple nerves.
Shoulder disorders like subacrominal bursitis, calcific tendonitis and adhesive capsulitis can look like Parsonage Turner Syndrome. Shoulder disorders typically will slowly progress, have previous symptoms displayed or have acute onset from trauma (a fall onto the shoulder or outstretched hand). The above noted shoulder disorders however can have acute onset of symptoms and mimic Parsonage Turner Syndrome. A thorough history and careful physical examination will differentiate these two disorders.
Thoracic outlet syndrome (see website for description) can occasionally mimic Parsonage Turner Syndrome. Thoracic outlet syndrome involves the brachial plexus just like Parsonage Turner Syndrome but in thoracic outlet syndrome , the nerves are pinched but not attacked by the immune system. In thoracic outlet syndrome, if the arm is left at the side of the body, the symptoms will disappear. In Parsonage Turner Syndrome, the symptoms are constant and position of the arm does not affect the pain. Also in thoracic outlet syndrome, muscle weakness is rare where in Parsonage Turner Syndrome weakness is typical.
For additional resources on Parsonage Turner Syndrome, please contact Dr. Donald Corenman, spine specialist and neck doctor serving the communities of Vail, Aspen, Denver and Grand Junction, Colorado.