Medial Antebrachial Cutaneous Nerve Injury After Brachial Plexus Block: Two Case Reports
A 62-year-old female patient presented to the Department of Anesthesiology of this hospital with the chief complaints of 1-month duration of pain and numbness in her right medial antebrachial region. She was referred to the Department of Rehabilitation for electrodiagnostic examinations. According to the patient's past history, she had undergone right carpal tunnel release 8 months before she visited our hospital. However, this did not relieve the complaint of right finger numbness that she had before the surgery. Therefore, she had undergone the surgery again one month earlier. The symptoms in the medial antebrachial region occurred thereafter. During the surgery, she was anesthetized by axillary brachial plexus block using ultrasound guidance. First, in a supine position, her arm was externally rotated by 90°, her elbow joint was flexed by 90°, and her head was turned to face the side opposite to the surgery. The ultrasonic probe was placed on the axillary region to find the axillary artery, the surrounding structures were checked, and a 23-G needle was inserted to inject a solution comprising a mixture of 2% lidocaine, 0.5% bupivacaine, and epinephrine (1:200,000) into the axillary sheath. Physical examinations revealed no muscle weakening but right thenar muscle atrophy. In sensory tests, the patient complained of decreased sensation and numbness in the right first, third, and fourth fingers, and in the medial antebrachial region. In particular, she reported that she suffered sleep disturbance due to the pain in the medial antebrachial region. The upper extremity deep tendon reflexes were all normal, but positive responses were obtained in the median nerve compression test. The symptoms were not accompanied by cervical and upper extremity pain, or decreased sensation. According to the electrodiagnostic examinations conducted 4 weeks after the onset of the symptom, the median and ulnar nerves were normal in motor nerve conduction studies. Sensory nerve conduction studies revealed a 4.10 ms delay in latency of the right median nerve and no response from the right MABC nerve (). Needle electromyography revealed no abnormal spontaneous activities in the abductor pollicis brevis muscle, which is innervated by the median nerve in the right-hand region.\nBased on the results of the physical and electrodiagnostic examinations, the patient was diagnosed with right MABC nerve injury. Pregabalin 75 mg, clonazepam 0.5 mg, and tramadol 50 mg were orally administered as drug treatment, and stellate ganglion block was performed. However, the patient's symptoms were not relieved. We decided to conduct outpatient follow-ups and periodic electrodiagnostic examinations. Eight weeks after the onset of the symptoms, the patient's pain was relieved slightly. In follow-up sensory nerve conduction study of the right MABC nerve, the latency on the right side was delayed by 5.00 ms compared to 2.50 ms on the unaffected left side, and the amplitude on the right side showed an abnormally reduced value of 2.9 µV compared to 10.1 µV on the left side. In addition, in the somatosensory evoked potential, the N20 latency of the right MABC nerve was delayed by 22.60 ms compared to 17.70 ms on the left unaffected side. The N20-P25 amplitude on the right side was 1.30 µV, showing a reduction of at least 50% compared to the left side (3.85 µV) ().