Thoracic Outlet Syndrome Caused by Schwannoma of Brachial Plexus
A 47-year-old woman visited the department of rehabilitation medicine complaining of pain, dysesthesia, and mild weakness in the intrinsic muscles of her right hand, each of which had persisted for approximately 1 year. The patient specifically reported dysesthesia and pain in her right upper arm, the medial part of her right forearm, and the fourth and fifth fingers of her right hand. There were no changes in color or pulse, and no indications of swelling or muscle atrophy. Plain cervical radiography and magnetic resonance imaging (MRI) were performed to rule out cervical or thoracic radiculopathy, but no specific abnormal findings were noted. Electrodiagnostic studies (EDS) showed that sensory and motor nerve conduction was normal. However, the F-wave study indicated slightly delayed onset latency at the right median and right ulnar nerves (right median, 27.8 ms; right ulnar, 27.8 ms). Needle electromyographic examinations of the right upper limb showed increased amplitude at the abductor pollicis brevis (APB) and reduced recruitment patterns at the APB and first dorsal interosseous (FDI). Results are presented in -. On physical examination, the Adson provocative test, hyperabduction maneuver, and elevated arm stress test were all positive. TOS was diagnosed. In the outpatient department, the patient received several forms of conservative management, including posture education, stretching exercises, trigger point injections, cervical stellate ganglion block, and medication. Despite this, her symptoms did not improve.\nNine months after receiving her first outpatient department treatment, the patient's symptoms were slightly aggravated. Motor power of the right finger intrinsic muscles was fair. The patient complained of a fixed and tender growing mass at the upper margins of her right clavicle. Ultrasonography revealed a 1.9×1.3×2.1-cm, well-marginated heterogeneous echoic mass at the lateral side of the right sternocleidomastoid muscle (). As ultrasonographic findings were strongly suggestive of a tumor, we performed enhancing right brachial plexus MRI, which revealed a 3.0×1.8×1.7-cm, well-marginated peripheral enhancing ovoid mass between the inferior trunk and the anterior division of the brachial plexus. T1-weighted images showed heterogeneous low signal intensity and T2-weighted images showed generally high signal intensity, with partial low signal intensity ().\nSubsequently, the patient was referred to the orthopedic department, where she underwent surgical mass removal. A biopsy was performed during surgery. On microscopic examination, hematoxylin and eosin staining revealed a strongly stained spindle cell neoplasm displaying Antoni A and Antoni B areas with Verocay bodies, which are characteristic findings of schwannoma (). After removal of the schwannoma, the weakness in the patient's right hand did not progress any further and her neuropathic pain gradually reduced. However, dysesthesia at the right C8 and T1 dermatome did not improve.\nTwenty-eight months after surgery, the patient underwent follow-up EDS. Needle electromyographic examinations showed increased amplitude and reduced recruitment patterns at the right APB, FDI, and abductor digiti minimi. Motor nerve conduction study showed that compound muscle action potential (CMAP) amplitudes of the right median and ulnar nerves were increased as compared with the previous test results (right median, 10.9 mV; right ulnar, 11.0 mV). The F-wave study for the right median and ulnar nerves indicated normal onset latency (right median, 24.8 ms; right ulnar, 26.7 ms).