Congenital anomalies of bony, fibrous, or muscular structures are often reported as etiologies of NTOS and can be associated with traumatic or functional causes. Bony anomalies, including cervical ribs and elongated C7 transverse processes, are reported to account for 30% of NTOS cases [
8]. Cervical ribs are known to have a prevalence of 0.5% to 2%, but they are rarely the cause of NTOS. Their prevalence in true NTOS, which requires a thorough documentation of objective findings of nerve compression for diagnosis, is even rarer, with only 1 in 20,000 to 80,000 cervical ribs leading to true NTOS [
8]. To our knowledge, the prevalence of elongation of the C7 transverse process has not yet been clearly reported. However, when clinical and electrodiagnostic findings suggest brachial plexopathy at the lower trunk level, the possibility of true NTOS caused by bony abnormalities increases [
8]. In our case, the elongation of the bilateral C7 transverse processes was confirmed by radiologic evaluations, in which the right transverse process was slightly longer than the left, corresponding to the symptoms and signs of true NTOS found only on the patient’s right side. Because true NTOS, an extremely rare disease, exhibits clinical symptoms similar to those of CTS, ulnar neuropathy, and cervical radiculopathies, it is often misdiagnosed, as in our case. If a patient exhibits problems only in the hand, as reflected in our case, NTOS is often mistaken for CTS [
6]. A physical examination of the median and ulnar nerves and special examinations for NTOS, such as the Roos stress test and Adson’s test, are helpful for establishing a clinical suspicion of NTOS. In the Roos stress test, the patient sits with full external rotation and 90° abduction of the shoulder joint and 90° flexion of the elbow joint, and repeatedly opens and closes the hand for 3 minutes. The provocation of pain or paresthesia is defined as a positive test finding (sensitivity, 52%-84%; specificity, 30%-100%). In Adson’s test, after the patient fully extends the elbow joint on the symptomatic side, the examiner palpates the radial pulse, as the patient turns the neck toward the symptomatic side while holding a deep breath. A change in the radial pulse indicates a positive test (sensitivity, 79%; specificity, 74%-100%) [
1,
3]. In order to exclude other possibilities from the differential diagnosis and confirm true NTOS, an electrodiagnostic study is essential [
3]. In nerve conduction studies, reduced median CMAP, ulnar and MABC SNAP amplitudes, and normal median SNAP and ulnar CMAP amplitudes indicate chronic axonal loss at the lower trunk level of the brachial plexus [
6,
9]. On needle electromyography, denervation potentials in C8- and T1-innervated muscles (dominant T1), including the APB, ADM, FDI, and other hand intrinsic muscles, are typical findings of true NTOS [
6,
9]. Abnormal MABC SNAP (sensitivity, 95%) and abnormalities in the APB (sensitivity, 97%) on needle EMG are highly sensitive for true NTOS [
7,
10]. In our case, the electrodiagnostic findings were compatible with those of true NTOS. In addition, this case is noteworthy due to the mild decrease in the right ulnar CMAP amplitude, abnormalities in the C8-innervated muscles in needle electromyography, and evidence of chronic denervation, such as high MUAP amplitudes instead of abnormal spontaneous activities, reflecting the patient’s long period of onset and severe atrophy. Based on the electrodiagnostic results and clinical findings that revealed no deterioration of symptoms in the past 3 months, it could be inferred that the denervation was not an ongoing process; thus, conservative treatment was recommended.
This is a rare case in which true NTOS was diagnosed 5 years after the onset of symptoms, during comprehensive rehabilitation that the patient received for left hemiplegia due to an unrelated cause. True NTOS is often overlooked or mistaken for CTS, thus delaying the diagnosis and inevitably worsening the outcomes. In addition to detailed history-taking and a physical examination, an electrodiagnostic study is crucial to detect brachial plexopathy and rule out other possibilities in the differential diagnosis, and radiologic evaluations may also be helpful.