Trauma is the common denominator in patients with omohyoid syndrome. The syndrome is most often seen in patients who have recently experienced a bout of intense vomiting or sustained a flexion/extension injury to the cervical spine and the musculature of the anterior neck.
The pain of omohyoid syndrome is the result of damage to the fibers of the inferior belly of the omohyoid muscle. This pain manifests as myofascial. It is constant and exacerbated with movement of the affected muscle.
A trigger point in the inferior belly of the omohyoid muscle is often present and provides a basis for treatment. The pain of omohyoid syndrome starts just above the clavicle at the lateral aspect of the clavicular attachment of the sternocleidomastoid muscle.
The pain may radiate into the anterolateral neck. Injection of the trigger point in the inferior muscle of the omohyoid muscle with local anesthetic and steroid serves as a diagnostic and therapeutic maneuver.
What are the Symptoms of Omohyoid Syndrome
Patients suffering from omohyoid syndrome present with pain in the supraclavicular region at a point just lateral and superior to the attachment of the sternocleidomastoid muscle to the clavicle. The pain often radiates into the anterolateral neck and increases with movement of the omohyoid muscle. A baseline level of pain is present even without movement of the muscle. The pain intensity ranges from minor to moderate.
A trigger point in the belly of the omohyoid muscle is often present. The pain of omohyoid syndrome is often exacerbated by swallowing. The neurological examination of a patient with omohyoid syndrome is normal, unless trauma has occurred to the cervical nerve roots or brachial plexus.
How is Omohyoid Syndrome diagnosed?
Magnetic resonance imaging (MRI) and/or ultrasound imaging of the soft tissues of the neck may reveal hematoma formation of the omohyoid muscle acutely and calcification, fibrosis, or both as the syndrome becomes more chronic.
Injection of the belly of the omohyoid muscle with local anesthetic can serve as a diagnostic maneuver to help strengthen the diagnosis.
Soft tissue injuries to the region may mimic omohyoid syndrome. Because trauma is invariably involved in the evolution of the painful condition, strain and sprain of other soft tissues often exist concurrently with omohyoid syndrome.
Sternohyoid syndrome as well as primary or metastatic tumors of the neck and hypopharynx also may mimic the clinical presentation of omohyoid syndrome and should be high on the list of diagnostic possibilities if the history of trauma is weak or absent.
Nonsteroidal antiinflammatory drugs (NSAIDs) or cyclooxygenase-2 (COX-2) inhibitors represent a reasonable first step in the treatment of omohyoid syndrome.
The use of tricyclic antidepressants, such as nortriptyline, at a single bedtime dose of 25 mg, titrating upward as side effects allow also is helpful, especially if sleep disturbance is present. The injection of trigger points in the inferior belly of the omohyoid muscle often produces dramatic improvement in pain symptoms.
The key landmark for injecting when treating omohyoid syndrome is the lateral aspect of the clavicular head of the sternocleidomastoid muscle.
The omohyoid muscle is located slightly lateral and deep to the clavicular head of the sternocleidomastoid muscle approximately ¾ to 1 inch above the superior margin of the clavicle. Given the relationship of the great vessels of the neck to the omohyoid muscle, care must be taken when placing needles in this anatomical area.
The patient is placed in the supine position, with the head turned away from the side to be blocked. Using a 5-mL sterile syringe, 3 mL of local anesthetic is drawn up.
When treating omohyoid syndrome, 80 mg of depot steroid is added to the local anesthetic with the first block, and 40 mg of depot steroid is added with subsequent blocks. The patient is asked to raise the head against the resistance of the pain specialist’s hand to aid in identification of the posterior border of the sternocleidomastoid muscle.
The point at which the lateral border of the sternocleidomastoid attaches to the clavicle is identified. At this point, slightly lateral and approximately 1 inch above the clavicle, after preparation of the skin with antiseptic solution, a 1½-inch needle is inserted directly perpendicular to the table top. The needle should be advanced slowly because of proximity of the great vessels and brachial plexus. A “pop” often is felt as the fascia of the omohyoid muscle is pierced; this should occur at a depth of ½ to ¾ of an inch.
If strict attention to technique is observed, and the needle is not placed or directed too laterally, the brachial plexus should not be encountered. Because of the proximity of the brachial plexus, the patient should be warned that a paresthesia could occur; the patient should be instructed to say “There!” if a paresthesia is felt. The needle should never be directed in a more inferior medial trajectory because pneumothorax is likely to occur.
After the muscle is identified, gentle aspiration is done to identify blood or cerebrospinal fluid. If the aspiration test is negative, and no paresthesia into the distribution of the brachial plexus is encountered, 3 mL of solution is slowly injected, with the patient being monitored closely for signs of local anesthetic toxicity or inadvertent neuraxial injection.
This technique can also be utilized for injection of botulinum toxin into the omohyoid muscle. Ultrasound guidance may improve the accuracy of needle placement and decrease the incidence of needle-related complications.
The major complication in the treatment of patients thought to have omohyoid syndrome is wrong diagnosis. Occult cervical spine fractures or instability after trauma remain an ever-present possibility. Failure to diagnose such injuries can put the patient at significant risk for permanent neurological sequelae. As mentioned earlier, if the history of trauma is suspect, the diagnosis of omohyoid syndrome should become one of exclusion.
A careful search for tumors of the neck, apex of the lung, anterior triangle of the neck, and hypopharynx is indicated. If a significant history of vomiting is ascertained, esophageal tear also should be considered.
Although the injection technique for omohyoid syndrome is safe, complications can occur. In addition to the potential for complications involving the vasculature, if the needle is placed too laterally, the proximity of the brachial plexus, the central neuraxial structures, and the phrenic nerve can result in side effects and complications.
Although these complications should be rare if proper technique is observed, the potential for inadvertent epidural, subdural, or subarachnoid injection remains a possibility. Inadvertent phrenic nerve block also can occur when using this injection technique to treat omohyoid syndrome if the needle placement is too far posterolaterally. In the absence of significant pulmonary disease, unilateral phrenic nerve block should rarely create respiratory embarrassment.
Inadvertent blockade of the recurrent laryngeal nerve with its attendant vocal cord paralysis combined with paralysis of the diaphragm may make the clearing of pulmonary and upper airway secretions difficult, however. Because of the proximity of the apex of the lung, pneumothorax is a distinct possibility and the patient should be informed of this.
Although an uncommon cause of pain, omohyoid syndrome is a clinically distinct and easily recognizable pain syndrome. Because of its excellent response to the injection technique described, the diagnosis of omohyoid syndrome should be considered in the presence of a history of trauma or after prolonged or forceful vomiting.
If the patient has severe, acute pain after vomiting, esophageal tear is a more likely diagnosis. More chronic pain after a significant episode of vomiting is more likely to indicate omohyoid syndrome.
The key to performing this injection technique safely is a clear understanding of the anatomy and careful identification of the anatomical landmarks necessary to perform the block. The brachial plexus is quite superficial at the level at which this block is performed.
The needle should rarely be inserted deeper than ¾ of an inch in all but the most obese patients. If strict adherence to technique is observed, and the needle is never advanced medially from the lateral border of the insertion of the sternocleidomastoid muscle on the clavicle, the incidence of pneumothorax should be less than 0.5%.
In the absence of well-documented trauma to the anterior neck, omohyoid syndrome is a diagnosis of exclusion. The clinician should always evaluate a patient with pain in this anatomical region for occult malignancy.
Tumors of the larynx, hypopharynx, and anterior triangle of the neck may manifest with clinical symptoms identical to omohyoid syndrome.
In the setting of flexion/extension injuries or other forceful trauma to the soft tissues of the neck, cervical spine, or both, the clinician also should evaluate the patient for trauma to the brachial plexus by careful physical examination and electromyography.