THE CLINICAL SYNDROME

• Both the biceps tendon and the brachialis muscle have the potential to compress and entrap the lateral antebrachial cutaneous nerve.

• In clinical observation, patients report pain and paresthesias that radiate from the base of the thumb all the way to the elbow.

• It is also common to experience a dull aching in the radial aspect of the forearm.

• In some cases, the pain of lateral antebrachial cutaneous nerve entrapment at the elbow may develop after an acute twisting injury to the elbow or direct trauma to the soft tissues that are overlying the lateral antebrachial cutaneous nerve.

• However, in other cases, the onset of pain is more insidious and there is no obvious inciting factor.

• The pain is always present and is made significantly worse by using the elbow.

• Patients who suffer from lateral antebrachial cutaneous nerve entrapment frequently report an increase in pain when performing activities such as playing the piano or using a computer keyboard.

• Compromise of the lateral antebrachial cutaneous nerve can also be seen after excessive use of the elbow, particularly after activities such as tennis and weightlifting that involve forced extension and maximal pronation of the elbow.

• A traction neuropathy can be caused when the nerve is displaced laterally as a result of a rupture in the proximal long head of the biceps muscle.

• Very infrequently, an injury to the nerve that results in neuropathy can take place as a result of venipuncture. It is common to experience problems sleeping.

SIGNS AND SYMPTOMS

• During the patient's physical examination, the physician found that the patient's lateral antebrachial cutaneous nerve was tender to palpation at a point just laterally to the biceps tendon.

• The range of motion at the elbow is typical.

• For patients suffering from lateral antebrachial cutaneous nerve entrapment, pain is experienced during active, resisted flexion of the forearm as well as rotation of the forearm.

TESTING

• An experienced electromyographer can diagnose lateral antebrachial cutaneous nerve entrapment with a high degree of accuracy, as well as distinguish it from other neuropathic causes of pain that may mimic it, such as radiculopathy and plexopathy.

• Electromyography and nerve conduction velocity studies are extremely sensitive tests.

• All patients who present with lateral antebrachial cutaneous nerve entrapment should have plain radiographs taken in order to rule out the possibility of hidden bony disorders.

• In the event that surgical intervention is being considered, magnetic resonance imaging (MRI) of the affected elbow may help to more precisely define the pathologic process that is causing the nerve entrapment (e.g., bone spur, aponeurotic band thickening).

• If a tumor of the brachial plexus, such as Pancoast's tumor or another type of brachial plexus tumor, is suspected, chest radiographs with apical lordotic views may be of assistance.

• In the event that the diagnosis is uncertain, screening laboratory tests, which include a complete blood count, erythrocyte sedimentation rate, antinuclear antibody testing, and automated blood chemistry, should be carried out in order to eliminate other potential reasons for the patient's pain.

• The nerve can be injected as a diagnostic and therapeutic maneuver all at the same time.

DIFFERENTIAL DIAGNOSIS

• Entrapment of the superficial radial nerve is one of the conditions that can cause symptoms similar to those of cervical radiculopathy and tennis elbow.

• The area that is the most tender to palpation in patients who have lateral antebrachial cutaneous nerve entrapment is at the level of the biceps tendon.

• In contrast, the area that is the most tender to palpation in patients who have tennis elbow is over the lateral epicondyle.

• Electromyography can differentiate between tennis elbow and other conditions, such as cervical radiculopathy and lateral antebrachial cutaneous nerve entrapment.

• In addition, the double-crush syndrome can occur when cervical radiculopathy and lateral antebrachial cutaneous nerve entrapment are present at the same time.

• The double-crush syndrome is most frequently observed in patients who also have carpal tunnel syndrome or median nerve entrapment at the wrist.

TREATMENT

• Patients who present with lateral antebrachial cutaneous nerve entrapment at the elbow are candidates for a brief course of conservative therapy consisting of simple analgesics, nonsteroidal antiinflammatory drugs, or cyclooxygenase-2 inhibitors, in addition to splinting to avoid elbow flexion.

• This course of treatment is indicated because it is safe and effective.

• A cautious injection of the lateral antebrachial cutaneous nerve at the elbow is a reasonable next step to take if the patient does not experience a significant reduction in their symptoms within one week.

• Surgical decompression of the lateral antebrachial cutaneous nerve is indicated in the event that the patient does not respond to these treatments or experiences progressive neurologic deficits.

COMPLICATIONS AND PITFALLS

• There is a risk of developing a permanent neurologic deficit if an entrapment of the lateral antebrachial cutaneous nerve at the elbow is not diagnosed and treated as soon as it occurs.

• Other causes of pain and numbness, such as Pancoast's tumor, may mimic the symptoms of lateral antebrachial cutaneous nerve entrapment.

• For the sake of the patient, the clinician needs to rule out these other potential causes of pain and numbness.

• The lateral antebrachial cutaneous nerve block at the elbow is a procedure that has a moderate risk of complications.

• Inadvertent intravascular injection into the lateral antebrachial cutaneous artery and persistent paresthesia as a result of needle-induced trauma to the nerve are the two major complications that can arise from this procedure.

• Because the nerve is surrounded by a dense fibrous band and travels through the lateral antebrachial cutaneous nerve sulcus, it is important to inject slowly just proximal to the sulcus in order to avoid further compromising the nerve.