Dorsal scapular nerve (DSN) entrapment syndrome is an under-recognized cause of neck and shoulder pain. DSN injuries can be the origin of a well-defined chronic pain syndrome, often referred to as DSN syndrome. DSN syndrome is often characterized by a dull ache along the medial border of the scapula. The dorsal scapular nerve may be injured in the neck (at the scalenes) or in the thoracic back at the level of the rhomboids.
Dorsal scapular nerve entrapment is a very under-recognized cause of neck and shoulder pain. The scapular winging may be subtle, and the symptoms are easily mistaken for other problems. A careful history and physical exam, along with a high index of suspicion, are necessary for accurate diagnosis and therefore appropriate treatment. Injection of the dorsal scapular nerve under ultrasound guidance can be diagnostic as well as therapeutic. Pulsed radiofrequency ablation of the dorsal scapular nerve may provide sustained pain relief.
Dorsal scapular nerve originates from the fifth cervical nerve root, with a possible contribution of C6 and after its origin runs in close proximity of the upper trunk of the brachial plexus, before piercing the middle scalene muscle and passing posteriorly, beneath the levator scapula muscle. It is responsible for the motor innervation of the levator scapula muscle itself, which elevates the scapula, and of both the rhomboid major and minor muscles, which pull the scapula medially. The nerve passes under the levator and then becomes more superficial between the rhomboid major and minor, as it travels caudally along the medial border of the scapula. The dorsal scapular artery goes between the middle and inferior trunks of the brachial plexus before the joining the dorsal scapular nerve as it leaves the middle scalene; the artery accompanies the dorsal scapular nerve to provide blood flow to the inferior trapezius muscle.
An isolated nerve injury can be seen in bodybuilders and in people who require heavy overhead lifting, because the dorsal scapular nerve may become entrapped within the scalenus medius muscle. It is also reported as a complication of the use of a spine brace for idiopathic scoliosis. The nerve may be injured in the neck during a brachial plexus block performed by the anaesthesists for regional block.
Because the DSN is often overlooked as a diagnosis, most patients with DSN entrapment have been misdiagnosed prior to the accurate diagnosis. Differential diagnosis includes:
Patients with dorsal scapular nerve entrapment mainly complain of pain over the medial border of the scapula. Patients may also experience interscapular pain, shoulder and arm pain, weakness of arm abduction, and/or winged scapula. They may complain of sharp, stabbing, burning, or knife-like medial scapular pain, lateral arm and forearm pain, neck and back dull ache, and a sense of “traction” within the shoulder. If DSN dysfunction is chronic, there may be rhomboid or levator atrophy. The onset of pain can be sudden or develop slowly over time. There may be a history of overhead work or overhead sports. Though DSN entrapment is considered quite rare, it may be greatly underrecognized, and it may be confused with or included with long thoracic nerve entrapment.
There may be concomitant anterior chest wall pain and tenderness over the sternocostal border, often with poorly localized ipsilateral arm pain that may be much more prominent than the interscapular pain. DSN entrapment can present as an “atypical” thoracic outlet syndrome.
Conservative treatment focuses on reducing secondary muscle tension and on improving posture. Non-pharmacological treatments like TENS and acupuncture can be tried.
Anti neuropathic drugs like tricyclic antidepressants and antiepileptics (gabapentin, pregabalin) can help relieve the symptoms.
Infiltration of local anaesthetic and steroid around the dorsal scapular nerve can be diagnostic and therapeutic as well. The injection is performed under real-time ultrasound guidance for greater accuracy and safety. The nerve can be targetted in the neck as in passes through the middle scalene muscle or in the posterior thorax as it passes under the Rhomboids.
Because of the substantial variability in the anatomy of the nerves and muscles in this highly vascular area of the neck, ultrasound guidance is particularly useful for DSN injections.
Pulsed radiofrequency lesioning of the dorsal scapular nerve is indicated in patients who show a positive response to the diagnostic dorsal scapular nerve block. This procedure can relieve symptoms associated with dorsal scapular nerve entrapment on a long-term basis. The procedure is performed under real-time ultrasound guidance and the DSN is ablated at 42 C for 480 seconds.
Injection of botulinum toxin in the rhomboid muscles can relieve the symptoms associated with DSN entrapment.