Abstract
Objective
The entrapment of the radial nerve at the spiral groove of the humerus in the arm segment (ERNAS) and traumatic radial neuropathy in the arm segment (TRNAS) are disorders that present with dropped hand. The aim of this study was to compare electrodiagnostic and clinical findings between patients with ERNAS and TRNAS, and to evaluate whether there is a correlation between these findings.
Method
This study was conducted at the Clinical Neurophysiology Laboratory of University of Health Sciences Turkey, Adana City Training and Research Hospital. ERNAS and TRNAS patients were included. The electrodiagnostic findings and the disabilities of the arm, shoulder and hand questionnaire (DASH) scores of the patients were reviewed in this retrospective study.
Results
Twenty-two ERNAS (20 male, 2 female) and 8 TRNAS (5 male, 3 female) patients were included. The mean ages of ERNAS and TRNAS patients were 45.5±16.1 and 45.0±13.8 years, respectively. The amplitudes of the superficial radial nerve compound nerve action potential (CNAP) and the radial nerve compound muscle action potential (CMAP) were significantly reduced in patients with TRNAS compared to those with ERNAS (p=0.002 and p=0.007, respectively). A negative correlation was identified between DASH scores and superficial radial sensory nerve conduction velocity (NCV) in ERNAS patients (p=0.001, r=-0.677).
Conclusion
This study indicated that superficial radial nerve CNAP and radial nerve CMAP amplitudes were more affected in TRNAS patients than in ERNAS patients. It was also concluded that there may be a relationship between superficial radial sensory NCV and clinical features.
Introduction
Radial nerve injury in the arm segment (RNIAS) may lead to sensory disturbances in the radial nerve distribution or with dropped hand, potentially leading to functional impairment of the upper extremity (1-4). RNIAS may occur due to trauma, such as a humeral fracture, or from compression of the radial nerve at the spiral groove of the humerus (1-4). Electrodiagnostic findings, along with clinical features, are essential for the diagnosis of RNIAS (1, 2). Electrodiagnostic tests crucial for diagnosis of RNIAS include conduction block of the radial motor nerve, slowing of radial motor nerve conduction velocity (NCV) across the arm segment, and needle electromyography (EMG) abnormalities in radial nerve innervated muscles (1, 2, 5). Patients with the entrapment of the radial nerve at the spiral groove of the humerus in the arm segment (ERNAS) and traumatic radial neuropathy in the arm segment (TRNAS) may have similar clinical and electrodiagnostic features. Therefore, this study focused on evaluating the clinical and electrodiagnostic characteristics in patients with TRNAS and ERNAS, as well as investigating the relationship between these features. Consequently, understanding the pathophysiology of RNIAS was also an objective.
Materials and Methods
Patients and Study Design
Patients exhibiting clinical and electrodiagnostic characteristics consistent with RNIAS, who were referred to the Clinical Neurophysiology Laboratory at University of Health Sciences Turkey, Adana City Training and Research Hospital between November 2018 and November 2022, were included. Clinical characteristics, findings of electrodiagnostic tests, and imaging methods of all patients were recorded in this retrospective study. Assessment of muscular function was achieved with the medical research council (MRC) scale (6). The disabilities of the arm, shoulder and hand questionnaire (DASH) were applied to all patients to evaluate upper extremity functions (7, 8). Additionally, the DASH work module and sports/performing arts module scores were recorded. The DASH questionnaire consists of 30 items assessing upper extremity function, each rated from 1 (no difficulty) to 5 (unable to perform), with the total score ranging from 0 (no disability) to 100 (severe disability). To obtain a valid score, at least 27 items must be completed (7, 8). The optional DASH work and sports/performing arts modules each include four additional items, designed for individuals engaged in those specific activities. Patients were considered to have RNIAS if the following features were present (2-5,9,10): 1) Dropped hand/fingers and/or sensory impairment in the cutaneous region innervated by the radial nerve on neurological examination; and 2) Radial motor NCV slowing or motor conduction block of the radial nerve in the arm segment and/or needle abnormality in radial nerve innervated muscles other than the triceps muscle. Patients with the listed conditions were excluded from the study: 1) Mononeuropathy other than radial neuropathy; 2) History of diseases that can lead to polyneuropathy, including diabetes mellitus 3) Polyneuropathy; 4) Neurodegenerative disease; and 5) Clinical features, electrodiagnostic results, and imaging methods were compatible with radiculopathy or brachial plexopathy. Patients who met the diagnostic criteria for RNIAS were divided into two groups according to the mechanism of onset. Patients who met the diagnostic criteria for RNIAS were included in the ERNAS group when symptom onset occurred after prolonged external compression during sleep, in the absence of any history of traumatic injury to the upper extremity. Patients with RNIAS whose symptom onset occurred after a documented traumatic event involving the upper extremity, specifically a humeral fracture, were included in the TRNAS group. Ethics committee approval was received from the Clinical Research Ethics Committee of University of Health Sciences Turkey, Adana City Training and Research Hospital (number: 118/2303, date: 15.12.2022).
Electrodiagnostic Tests
Nerve conduction study and needle EMG were performed on the Cadwell Sierra Summit EMG unit (Cadwell Laboratories, Kennewick, Washington, USA). Electrodiagnostic tests were performed if the extremity temperature was 32 degrees or above. In motor and sensory nerve conduction study, low-high filters were set as 20 Hz-10 kHz and 20 Hz-2 kHz, respectively. Surface electrodes were employed in stimulation. Recording was done with disc electrodes. For the motor-sensory nerve conduction study, sweep speed and sensitivity were set as 5-1 ms/division and 2000-10 µV/division, respectively. Recommended methods were used for median, ulnar and superficial radial nerve conduction studies (11-13). In median and ulnar motor nerve conduction studies, recordings were obtained from the abductor pollicis brevis and abductor digiti minimi muscles, respectively. Median and ulnar sensory nerve conduction studies were performed antidromically in the index finger-wrist and little finger-wrist segments, respectively. Amplitudes were measured peak to peak, and sensory nerve conduction velocities were calculated using peak latency. Normal values from the test laboratory were used for reference values in median and ulnar nerve conduction studies (13). For superficial radial sensory nerve conduction studies, recordings were obtained from the anatomical snuffbox region, with the reference electrode placed on the thumb. The nerve was stimulated 12-14 cm proximal to the recording electrode along the radial aspect of the forearm, and sensory NCV was calculated using the peak latency. The lower reference value for superficial radial nerve NCV and compound nerve action potential (CNAP) amplitude was set as 35.7 m/s, 11 µV, respectively (12). Superficial radial nerve CNAP amplitude was considered abnormal if the superficial radial nerve CNAP amplitude was lower than the reference value or reduced by more than 50% compared to the contralateral superficial radial nerve CNAP amplitude. In the radial motor nerve conduction study, recording was conducted using a concentric electrode (length=50 mm, diameter=0.46 mm, Bionen Medical Devices, Florence, Italy; length=50 mm, 26 G, Natus, Galway, Ireland). The recording was made in the extensor indicis proprius muscle. The stimulation points were 4 cm proximal to the recording electrode, 5-6 cm proximal to the lateral epicondyle and the ERB point. The lower reference values for radial motor NCV for the distal and proximal segments were 49.8 m/s and 59.4 m/s, respectively (11). If radial nerve compound muscle action potential (CMAP) could not be obtained, the radial nerve CMAP amplitude was considered abnormal. Motor conduction block was identified as a reduction of more than 50% in the CMAP amplitude from proximal stimulation relative to the CMAP amplitude from distal stimulation.
Needle EMG was applied with concentric needle electrodes. The low-high filter was set to 10 Hz-10 kHz. Sensitivity and sweep speed for spontaneous activity were 100 µV/division and 10 ms/division, respectively. Sensitivity and sweep speed for motor unit action potential (MUAP) examination were 0.5-1 mV/division and 10 ms/division, respectively. The presence of spontaneous discharges at rest was carefully evaluated. MUAP amplitude >3.5 mV or MUAP duration >15 ms was considered neurogenic MUAP. Needle EMG was applied to the extensor indicis proprius, extensor digitorum communis, brachioradialis, triceps, first dorsal interosseous and deltoid muscles in all patients. Additionally, in some patients, the abductor pollicis brevis, biceps brachii and cervical paraspinal muscles were examined with needle EMG for differential diagnosis.
Statistical Analysis
Nominal variables were described using rates and percentages. Numerical variables were reported as mean ± standard deviation, median, and minimum-maximum. Pearson’s chi-square test was used to analyze categorical data between groups. The Mann-Whitney U test was employed for comparing numerical variables across groups. Spearman rank correlation analysis was conducted to assess relationships between variables. A p-value of less than 0.05 was considered statistically significant. Statistical analysis was performed using SPSS version 22.0.
Results
Among the 44 reviewed RNIAS patients (26 ERNAS, 18 TRNAS), 14 were excluded from the study. Two of the ERNAS patients had carpal tunnel syndrome, one had diabetes mellitus, and one had cervical radiculopathy. Three of the TRNAS patients had diabetes mellitus, four had carpal tunnel syndrome, one had ulnar neuropathy, one had cervical radiculopathy, and one had polyneuropathy associated with thyroid disease. These patients were excluded from the study. Ultimately, twenty-five male and five female RNIAS patients were included. The mean age and body mass index of the patients were 45.4±5.3 (min-max 22-69) years and 24.8±2.9 (18.8-31.2) kg/m2, respectively. The mean duration of illness was 55.4±41.9 (15-180) days. There were 22 ERNAS (20 male, 2 female) and 8 TRNAS patients (5 male, 3 female) (p=0.101 for gender). The mean ages (min-max) of ERNAS and TRNAS patients were 45.5±16.1 (22-69) and 45.0±13.8 (29-67) years, respectively (p=0.907). The mean durations of disease in TRNAS and ERNAS patients were 103.4±50.4 and 38.1±19.9 days, respectively (p<0.005).
RNIAS was identified in 17 patients affecting the right arm and in 13 patients affecting the left arm. Five ERNAS patients had a history of alcohol use, and two ERNAS patients had a history of narcotic use. Other ERNAS patients had a history of radial neuropathy that developed only after prolonged sleep. In 19 of the patients (63%), sensory impairment in the cutaneous area supplied by the superficial radial nerve was present during the neurological assessment. Sensory abnormalities were present in twelve ERNAS patients (55%) and seven TRNAS patients (88%) (p=0.199). All patients had muscle weakness in at least one of the radial innervation muscles. The mean (min-max) MRC scores of finger extension, wrist extension and brachioradialis muscles were 2.0±1.4 (0-4), 2.3±1.7 (0-5), 3.2±1.5 (0-5), respectively. The mean scores of DASH, DASH-work module and DASH-sports performing arts module were 50.2±28.3 (number=30), 57.9±29.3 (number=29), 50.0±27.7 (number=6), respectively. Superficial radial CNAP amplitude and NCV were 22.7±19.6 µV and 52.9±10.9 m/s, respectively. The radial motor nerve distal CMAP amplitude, the NCV and the percentage of amplitude reduction in the arm segment were 4.8±4.0 mV, 51.7±14.5 m/s and 68.9±30.9%, respectively. The comparison of clinical and electrodiagnostic findings between TRNAS and ERNAS patients is presented in Table 1. Table 2 shows the abnormalities found in the electrodiagnostic tests of the patients.
Figure 1 shows ERNAS and TRNAS patients with superficial radial nerve CNAP and radial nerve CMAP abnormalities. Table 3 shows the correlation between nerve conduction study and DASH scores in patients. There was a significant negative correlation between DASH scores and the superficial radial nerve NCV in ERNAS patients and in the overall RNIAS cohort (p=0.001, r=-0.677 for ERNAS patients; p=0.044, r=-0.406 for all RNIAS patients). Figure 2 shows the correlation between superficial radial NCV and DASH scores in ERNAS patients.
Discussion
In this study, the correlation between clinical features and electrodiagnostic findings in RNIAS patients was investigated. A negative correlation was found between DASH scores and superficial radial nerve NCV in ERNAS patients. Superficial radial nerve CNAP amplitudes and radial nerve CMAP amplitudes were found to be lower in the patients with TRNAS than in the patients with ERNAS.
The etiology of radial neuropathy includes conditions such as humeral fracture and systemic diseases (1, 3, 4). Another reason is ERNAS. This condition is also referred to as saturday night palsy (1, 4, 9). Similar to the characteristics of the patients in this current study, saturday night palsy can be seen after prolonged sleep as a result of alcohol or substance use, or after surgery (1, 3, 4). Demyelination contributes fundamentally to the pathophysiology of ERNAS patients (1, 5, 9). In radial neuropathy in the arm segment, patients present with a droopy hand (1, 3, 4). Sensory abnormalities in the distribution of the superficial radial nerve were noted in a substantial portion of patients, especially among those with ERNAS. This may be related to the demyelinating nature of ERNAS, where conduction impairment can occur without significant axonal loss. On the other hand, more pronounced sensory symptoms may develop in axonal lesions such as those seen in TRNAS. Nevertheless, since the difference between the groups did not reach statistical significance, these observations should be interpreted with caution. Previous studies have shown that demyelinating neuropathies generally have a more favorable prognosis than axonal injuries, particularly in terms of functional recovery (1, 2, 14).
Electrodiagnostic tests can provide important clues about the prognosis of RNIAS patients. The prognosis of nerve damage accompanied by axonal degeneration tends to be worse than the prognosis of nerve damage with demyelination alone (1, 2, 10, 14). Recovery may be delayed or incomplete in axonal degeneration (1, 2, 5). Demyelination is predominant in ERNAS patients, and most ERNAS patients recover fully or almost completely in the first few months (1, 5, 9). Recovery rarely takes up to six months. In this current study, the radial nerve CMAP amplitudes of TRNAS patients were found to be lower than the CMAP amplitudes of ERNAS patients. This finding indicates that the type of radial nerve injury in ERNAS patients is compatible with segmental demyelination, and that the type of radial nerve injury in TRNAS patients is compatible with axonal degeneration. In light of this information, it can be said that the recovery in TRNAS patients may be later or worse than the recovery in ERNAS patients.
Radial nerve CMAP amplitude abnormality, radial motor nerve conduction block in the arm segment, radial motor NCV abnormality, and superficial radial nerve CNAP abnormality constitute the nerve conduction study findings in ERNAS and TRNAS patients (1, 2, 5). Motor conduction block and needle EMG abnormalities did not differ between ERNAS and TRNAS patients. As previously mentioned, there were electrodiagnostic difference between ERNAS and TRNAS patients in terms of abnormalities in radial nerve CMAP and superficial radial nerve CNAP amplitudes.
In this current study, a relationship was found between DASH scores and some electrodiagnostic findings. An inverse correlation was found between the severity of conduction block and DASH score in ERNAS patients. As the conduction block improves, the weakness may improve (15, 16). Additionally, an inverse correlation was found between superficial radial nerve NCV and DASH scores of ERNAS patients and all RNIAS patients. Conduction block and superficial radial sensory NCV may have significant benefits in the follow-up of ERNAS patients. A reduced radial nerve CMAP amplitude in TRNAS patients may be associated with poor prognosis.
Study Limitations
There were some limitations in this study. Disease duration was different significantly between ERNAS and TRNAS patients and should be considered an important potential confounder. In addition, the disease durations of patients within the same groups also differed. Electrodiagnostic test findings and clinical features may be influenced by disease duration (17). We think that this difference is caused by the fact that ERNAS patients are admitted in the acute period and TRNAS patients are initially presented with splints or injuries or are admitted after emergency surgical intervention. Despite this duration variability, we believe that the observed differences in parameters such as CMAP and CNAP amplitudes reflect inherent differences in nerve involvement patterns, with demyelination being more common in ERNAS and axonal damage more prominent in TRNAS. Nevertheless, the potential impact of disease duration should be acknowledged when interpreting the results, and the findings should be interpreted with appropriate caution. The low number of TRNAS patients was also a limitation, but it should be kept in mind that the exclusion criteria in the current study were strict. However, studies that do not have strict exclusion criteria and include patients with diseases that can cause polyneuropathy, such as diabetes mellitus, or those with polyneuropathy may benefit from elucidating the pathophysiology and clinical features of radial neuropathy.
Conclusion
In summary, this study showed that radial nerve CMAP and superficial radial nerve CNAP amplitudes in TRNAS patients were lower than those in ERNAS patients. This may indicate that the prognosis in TRNAS patients is worse than in ERNAS patients. These findings should be interpreted with consideration of the differing disease durations between groups, as this may have influenced the degree of nerve injury observed on electrodiagnostic testing. It was found that there may be a relationship between superficial radial sensory NCV/radial motor nerve conduction block and clinical features in ERNAS patients. A similar relationship existed between radial nerve CMAP amplitude and clinical features in TRNAS patients.
