Abstract
Purpose
Patient-reported outcomes are used routinely to assess disease severity in patients with cubital tunnel syndrome (CuTS). This study aimed to compare the relationships of patient-reported outcomes with clinical examination, electrodiagnostic (EDX), and ultrasound (US) measures.
Methods
Twenty-four patients presenting to an academic center with symptoms consistent with isolated CuTS were prospectively enrolled. Clinical examination measures were collected, including grip strength, key pinch, 2-point discrimination, presence of Tinel sign, and elbow flexion test result. Patients underwent EDX evaluation, and US was used to measure the cross-sectional area of the ulnar nerve around the elbow. Patients completed 3 questionnaires: Patient-Rated Ulnar Nerve Evaluation (PRUNE), Patient-Reported Outcomes Measurement Information System (PROMIS), and Disabilities of the Arm, Shoulder, and Hand (DASH). Questionnaire scores and clinical examination measurements were stratified based on EDX and US status. Pearson’s correlations were used to assess the associations of questionnaire scores with objective measures.
Results
Significant correlation in PROMIS-Physical Function (PROMIS-PF), PROMIS-Pain Interference (PROMIS-PI), PROMIS-Depression (PROMIS-D), PROMIS-Upper Extremity (PROMIS-UE), and DASH scores were observed between EDX−positive and -negative groups, while no significant correlation was seen between US- positive and -negative groups. Two-point discrimination significantly correlated with PRUNE, PROMIS-PF, PROMIS-UE, and DASH scores. All patient-reported outcome measures significantly correlated with sensory amplitude. PROMIS-D weakly correlated with maximum ulnar nerve cross-sectional area. No significant correlations between patient-reported outcome measures and motor EDX outcomes were observed.
Conclusions
Patient-reported symptom severity is more closely associated with EDX diagnosis than US status. PROMIS-PF and DASH displayed stronger correlations to objective measures than other patient-reported outcome measures. Sensory amplitude was the strongest predictor of subjective symptom severity relative to other measures.
Type of study/level of evidence
Diagnostic II.
Key words: Cubital tunnel, Electrodiagnostic, EMG, UNE, Ultrasound
Cubital tunnel syndrome (CuTS) is the second most common peripheral entrapment neuropathy after carpal tunnel syndrome, with an estimated 72,000 cases per year in the United States.1 Validated patient-reported outcome measures (PROMs), such as Patient-Rated Ulnar Nerve Evaluation (PRUNE), Disabilities of the Arm, Shoulder, and Hand (DASH), and Patient-Reported Outcomes Measurement Information System (PROMIS) have been proposed to assess disease severity in patients with CuTS with the most disease-specific questionnaire for assessing CuTS severity currently being PRUNE.2 However, the DASH questionnaire also has been demonstrated to be a valid, reliable, and responsive assessment tool for CuTS as it is for shoulder impingement and basal joint arthritis.3, 4, 5, 6 On the other hand, data on the validity of PROMIS in the evaluation of CuTS are limited. A single study demonstrated that for patients undergoing cubital tunnel decompression, PROMIS was responsive early in the recovery course but lacked the sensitivity to show postoperative improvement after 6 weeks.7
In addition to PROMs, several clinical assessments are used regularly to evaluate CuTS symptoms, such as Tinel sign, elbow flexion test, grip strength, key pinch, and 2-point discrimination. However, the relationships between these measures and patient-reported symptom severity have yet to be elucidated thoroughly. Few studies have assessed directly the correlations of PROMs with objective clinical examination measures.8,9 Specifically, a gap remains in our understanding of the relationship between PROMIS scores and clinical examination measures in the setting of CuTS despite its growing adoption in evaluating other musculoskeletal pathologies.
Alongside clinical examination measures, the predominant diagnostic modalities for CuTS are electrodiagnostic studies (EDX) and ultrasound (US). Numerous studies have focused on describing the sensitivities of these tests in the setting of CuTS diagnosis (EDX, 37% to 86% sensitivity; US, 70% to 93.8% sensitivity), and others have compared how EDX measures relate to US outcomes in the setting of ulnar nerve entrapment.10, 11, 12, 13, 14, 15, 16, 17 However, evidence is limited on how EDX and US outcomes relate to the subjective disease experience of the patient. Ideally, diagnostic modalities not only should detect pathology but also be able to approximate subjective symptom severity in patients. Furthermore, with several options available to providers, there is increasing interest in understanding which PROMs correlate to the objective pathologic findings consistent with CuTS.
This study aims to compare the relationships of PRUNE, PROMIS, and DASH with clinical examination, and electrodiagnostic and ultrasound measures. Given that US has been described as a potentially more sensitive tool for diagnosing CuTS than EDX, we hypothesize that US diagnostic outcomes will have a greater correlation with PROMs than EDX.10, 11, 12, 13, 14, 15 We also hypothesize that PRUNE scores will be associated more closely with objective measures since PRUNE was designed and validated specifically for ulnar nerve evaluation.
Materials and Methods
Patient recruitment and study design
This institutional review board-approved prospective study included patients aged >18 years who presented to a tertiary academic medical center with clinical signs and symptoms consistent with CuTS, such as a tingling sensation along the fifth digit or medial half of the fourth digit, or weakness of the hand. Patients were collected consecutively over a 2-year period. After providing informed consent, enrolled patients underwent physical examination by a board-certified, fellowship-trained hand surgeon. They were diagnosed clinically with CuTS based on the presence of any of the following physical examination findings: the presence of numbness and paresthesia of the fourth and fifth digits of the hand, weakness of the hand muscles innervated by the ulnar nerve, Tinel sign at the elbow, positive elbow flexion test, first dorsal interosseus atrophy, or flattening of the palm. Patients were referred for EDX evaluation as per the standard of care. Patients with a history of systemic diseases or medical conditions potentially associated with polyneuropathy (diabetes mellitus, hypothyroidism, rheumatoid arthritis, amyloidosis, pregnancy, and chronic renal failure treated by hemodialysis), cervical radiculopathy, acute trauma, or ulnar nerve surgery were excluded.
Additionally, patients who displayed evidence of moderate-to-severe carpal tunnel syndrome based on electrodiagnostic criteria were excluded to avoid confounding. Clinical examination measures, such as grip strength, key pinch, fifth digit 2-point discrimination, Tinel sign, and elbow flexion test results, were recorded for each patient. Ultrasound measurements of the ulnar nerve’s Maximum Cross-Sectional Area (Max CSA) around the affected and contralateral elbow were obtained. Patients completed the following questionnaires at the end of their visits: PRUNE, PROMIS, and DASH.
Clinical examination measures
Grip and key pinch strengths were measured in pounds using a Jamar hydraulic hand dynamometer (Sammons Preston) and hydraulic pinch gauge (Sammons Preston). Measurements were recorded across 3 trials and then averaged to obtain a final measurement for each side. Static small finger 2-point discrimination measurements were obtained at the small finger pulp using a Jamar discriminator (Sammons Preston) and recorded in millimeters for the affected and contralateral sides. Measurements were obtained while patients were seated and blindfolded. Recordings across 3 trials were acquired and averaged to yield a single aggregate result.
Patient questionnaires
The PRUNE, PROMIS, and DASH questionnaires were administered to patients via Apple iPads (Apple Inc) after being evaluated by a board-certified hand surgeon during their initial visit. The “Total” score PRUNE category was recorded and represented the PRUNE scores in this study. Specific PROMIS surveys that were assessed in this study included: “Physical Function” (PROMIS-PF v1.2/2.0), “Pain Interference” (PROMIS-PI v1.1), “Upper Extremity” (PROMIS-UE v2.0), and “Depression” (PROMIS-D v1.0). For DASH, the 30-item DASH disability survey was administered, and a single score was obtained.
Electrodiagnostic studies
Patients provided verbal informed consent before performing upper limb EDX studies. Patients then were evaluated with a focused neuromuscular history and physical examination before performing an EDX study. The EDX studies were completed using a Cadwell Sierra Summit machine (Cadwell Industries). Upper limb temperature was maintained at 32 °C. Each patient was assessed, at a minimum, with ulnar sensory and motor, median sensory and motor, and radial sensory nerve conduction studies. Nerve conduction was recorded, and reference values were consulted in accordance with the American Association of Neuromuscular and Electrodiagnostic Medicine (AANEM) practice guidelines.18 Patients meeting the AANEM criteria for ulnar neuropathy were considered diagnostically abnormal by EDX and denoted as EDX+, while those who failed to meet AANEM thresholds were considered EDX−. Concentric needle evaluation of ulnar and nonulnar innervated muscles was performed to assess for additional neuromuscular conditions, including cervical radiculopathy, brachial plexopathy, and other upper limb neuropathies.
Ultrasound measurements
Bilateral CSA measurements of the ulnar nerve were obtained 3 cm proximal to the cubital tunnel (inlet), within the cubital tunnel (between the medial epicondyle and the olecranon), and 3 cm distal to the cubital tunnel (outlet) using a SonoSite SII ultrasound machine with a 15MHz transducer (HFL50X). The “trace” function was used to trace the inside of the hyperechoic rim of the ulnar nerve. The Max CSA subsequently was calculated by the computer software and recorded in mm2. Patients with a Max CSA of 10 mm2 were denoted as US+, while patients with a Max CSA of <10 mm2 were considered US−. This cross-sectional area cutoff value was used as it is a widely accepted threshold for diagnosing CuTS.15,19,20
Statistics
Descriptive statistics were used to characterize demographics and symptom severity among the cohort. Clinical examination measures and questionnaire scores stratified by EDX/US status were compared using an independent samples t-test. Pearson’s correlation coefficients (r) were used to assess the association between questionnaire scores and clinical examination measures in addition to EDX/US outcomes. The strength of correlations was interpreted according to the following ranges: weak (|0.3| ≤ r < |0.5|), moderate (|0.5| ≤ r < |0.7|), and strong (≥0.7|). P < .05 was considered statistically significant for all analyses.
Results
A total of 24 patients met the required inclusion/exclusion criteria. Basic demographic variables are included in the Table 1. Summary statistics of disease severity among the cohort are described in the Table 2. Twenty-one patients had a positive Tinel sign at the elbow and 17 had a positive elbow flexion test. There were 12 patients diagnosed as EDX+, 12 EDX−, 17 US+, and 7 US−. Among patients stratified by EDX result, key pinch was the only clinical examination measure that differed significantly between EDX+ and EDX− groups (P = .01; Fig. 1A). When comparing patients stratified by US diagnostic status, no significant correlation was found in the objective assessment of key pinch, grip strength, or 2-point discrimination (Fig. 1B). Significant correlation in PROMIS-PF (P = .002), PROMIS-PI (P = .04), PROMIS-D (P = .01), PROMIS-UE (P = .01), and DASH (P = .007) scores were observed between EDX groups (Fig. 2A). There was no significant difference in PRUNE scores between EDX− and EDX+ groups (P = .16). Additionally, there were no significant correlation in questionnaire scores among patients stratified by US outcome (Fig. 2B).
Table 1.
Patient Demographics
| Variable | ||
|---|---|---|
| Age (mean; range) | 51.9 (25.5–80.4) |
|
| No. | % | |
| Sex | ||
| Male | 6 | 24.0% |
| Female | 19 | 76.0% |
| Affected Side | ||
| Left | 13 | 52.0% |
| Right | 12 | 48.0% |
Table 2.
Descriptive Statistics of Cohort Disease Severity
| Variable | Mean | SD | Min | Max |
|---|---|---|---|---|
| Sensory peak latency (ms) | 3.2 | 0.4 | 2.7 | 4.3 |
| Sensory amplitude (μV) | 22.2 | 15.5 | 1.0 | 55.0 |
| Elbow motor amplitude (mV) | 9.2 | 2.2 | 4.8 | 12.6 |
| Elbow motor conduction velocity (m/s) | 56.8 | 9.1 | 44.0 | 80.0 |
| Max CSA (mm2) | 12.7 | 4.5 | 5.0 | 26.0 |
| ΔGrip strength (lbs) | −12.5 | 22.3 | −60.0 | 20.7 |
| ΔKey pinch (lbs) | −2.2 | 3.5 | −10.7 | 1.7 |
| Two-point discrimination (mm) | 8.2 | 5.9 | 2 | 20 |
| PRUNE | 40.9 | 21.8 | 4.5 | 91.5 |
| PROMIS-physical function | 43.6 | 9.1 | 27 | 59 |
| PROMIS-pain interference | 58.1 | 9.0 | 39 | 75 |
| PROMIS-depression | 52.2 | 10.4 | 34 | 71 |
| PROMIS-upper extremity | 36.7 | 9.0 | 22 | 56 |
| DASH | 33.1 | 22.8 | 4 | 79 |
Figure 1.
Comparison of grip strength, key pinch, and fifth digit 2-point discrimination measurements among patients stratified by A EDX and B US diagnostic status. Grip strength and key pinch measurements represent absolute correlation relative to the contralateral side. ∗ P < .05.
Figure 2.
Correlation in PRUNE, DASH, and PROMIS scores among patients stratified by A EDX and B US status. ∗P < .05, ∗∗P < .01.
Among clinical examination measures, PRUNE only correlated with fifth digit 2-point discrimination (r = 0.511, P = .02). Additionally, fifth digit 2-point discrimination significantly correlated with PROMIS-PF (r = −0.518, P = .02), PROMIS-UE (r = −0.459, P = .04), and DASH (r = 0.550, P = .01) scores. Significant associations between grip strength, key pinch, presence of Tinel, and elbow flexion test results with PROMs were not observed (Table 3).
Table 3.
Pearson Correlation Coefficients Describing the Relationship Between PROMs and Objective Clinical Measures
| Variable | ΔGrip Strength | ΔKey Pinch | 2-point Discrimination (5th Digit) | Tinel Sign | Elbow Flexion Test |
|---|---|---|---|---|---|
| PRUNE | −0.236 | −0.316 | 0.511∗ | −0.151 | −0.187 |
| PROMIS-physical function | 0.238 | 0.212 | −0.518∗ | 0.161 | 0.044 |
| PROMIS-pain interference | −0.378 | −0.185 | 0.356 | 0.188 | 0.070 |
| PROMIS-depression | 0.290 | −0.033 | 0.435 | -0.080 | −0.017 |
| PROMIS-upper extremity | 0.342 | 0.206 | −0.459∗ | 0.094 | 0.218 |
| DASH | −0.220 | −0.257 | 0.550∗ | -0.100 | −0.121 |
P < .05.
Among EDX and US outcomes, PRUNE solely correlated with sensory amplitude (r = −0.427, P = .04) (Table 4). All other PROMs significantly correlated with sensory amplitude: PROMIS-PF (r = 0.669, P < .01), PROMIS-PI (r = −0.490, P = .02), PROMIS-UE (r = 0.467, P = .03), and DASH (r = −0.600, P < .01) (Table 4). The PROMIS-D was the only PROM to correlate significantly with Max CSA (r = 0.445, P = .04). Significant correlations with motor EDX outcomes were not observed. (Table 4).
Table 4.
Pearson Correlation Coefficients Describing the Relationship Between PROMs and EDX/US Outcomes
| Variable | Sensory Peak Latency | Sensory Amplitude | Elbow Motor Amplitude | Elbow Motor Conduction Velocity | Max CSA |
|---|---|---|---|---|---|
| PRUNE | 0.089 | −0.427∗ | 0.168 | −0.041 | 0.033 |
| PROMIS-physical function | −0.418 | 0.621† | 0.153 | 0.317 | −0.030 |
| PROMIS-pain interference | 0.356 | −0.488∗ | -0.117 | -0.378 | 0.039 |
| PROMIS-depression | 0.491∗ | −0.485∗ | 0.079 | −0.066 | 0.445∗ |
| PROMIS-upper extremity | −0.402 | 0.426∗ | 0.318 | 0.257 | −0.029 |
| DASH | 0.406 | −0.628† | -0.225 | −0.382 | 0.081 |
P < .05.
P < .01.
Discussion
Validated PROMs, such as PRUNE, PROMIS, and DASH, have been used to assess disease severity in patients with CuTS, with the most disease-specific questionnaire currently being PRUNE. However, a formal comparison of these PROMs and their association with objective clinical measures has yet to be conducted in the setting of CuTS. The primary objective was to compare the correlation of these 3 questionnaires with clinical examination findings, EDX, and US measures.
In our cohort, subjective symptom severity as defined by PROM scores more accurately correlated with EDX rather than US status. Specifically, PROMIS-PF, PROMIS-PI, PROMIS-D, PROMIS-UE, and DASH scores differed significantly among patients stratified by EDX status. Conversely, there were no significant correlations in questionnaire scores among patients stratified by US outcome. Several studies have described associations between the ulnar nerve Max CSA and EDX severity in CuTS.13,19, 20, 21 However, the relationship between Max CSA and patient-reported symptom severity is not well defined. Our results suggest that abnormal ulnar nerve findings by US may not always be as reflective of subjective symptom severity compared to EDX status. Nevertheless, the value of US as a diagnostic modality for CuTS, and its ability to localize sites of compression in patients remains important.
Sensory amplitude was the strongest predictor of subjective symptom severity relative to other EDX/US measures and correlated with all PROMs examined in the study. No significant correlations with motor conduction velocity at the elbow were observed. It is possible that, by the time the disease progresses to the point that (the more robust) motor fibers are affected, patients may have acquired higher tolerance to the discomfort and modified their activities to compensate for their potential weakness.22 Overall, these results suggest that damage to sensory fibers may potentially more accurately reflect the experience of symptom severity in CuTS patients compared to pathology affecting motor fibers.
Overall, PROMIS-PF and DASH displayed more robust correlation to preoperative clinical measures relative to PRUNE and other PROMs. Specifically, these measures were correlated moderately with sensory amplitude and 2-point discrimination. Also, PRUNE solely correlated with sensory amplitude and 2-point discrimination, although the associations were weak. These results contrast those of Szekeres et al8, who did not demonstrate a significant correlation between 2-point discrimination and preoperative PRUNE scores.
Limited evidence currently is available on the validity of the PROMIS questionnaire for assessing CuTS symptoms, particularly at the preoperative time point. To our knowledge, only one study has investigated the role of PROMIS in the assessment of CuTS, while PRUNE has long been accepted as a validated instrument and incorporated in numerous studies.7,8,23, 24, 25 Phan et al7 demonstrated that PROMIS-PF, PROMIS-UE, and PROMIS-PI exhibits sufficient sensitivity to track postoperative symptom improvement up to 6-weeks following cubital tunnel decompression surgery but lacked the sensitivity to track improvement beyond a 6-week time point. Our results suggest that PROMIS-PF, may be a more sensitive indicator of preoperative symptom severity than PRUNE and other PROMIS measures. Although PRUNE is the currently accepted gold standard for evaluating CuTS symptom severity, our results highlight an important role for the use of PROMIS-PF in the preoperative assessment of CuTS.
There were several significant limitations in this study. First, despite excluding patients with concurrent moderate-to-severe carpal tunnel syndrome, some patients with mild carpal tunnel syndrome were included, which may affect some patient responses on questionnaires or their clinical examination measures. Second, the potential to detect further significance may have been limited by the number of patients included in the study. Nevertheless, even with this sample size, we still could observe robust trends that allowed us to draw conclusions comparing the instruments used in CuTS evaluation. Third, the subjects presented to a single tertiary academic center in the Northeast United States, and the results may not be generalizable. Lastly, the weak correlation between PROMIS-D and US status may describe a causal relationship between cubital tunnel syndrome and psychologic affects. However, given the weak correlation, this relationship may be spurious. Further work addressing this study’s relationships is needed across a broader range of geographic areas.
In summary, our prospective study comparing the relationships of PROMs to clinical, EDX, and US measures revealed that subjective symptom experience more closely correlates to EDX diagnosis rather than US findings. We also showed that sensory amplitude is the strongest predictor of patient-reported symptom severity than other objective measures and that PROMIS-PF and DASH correlate most closely with objective measures. Overall, our findings highlight the tools that provide a more accurate assessment of CuTS symptom severity which can improve provider interpretation of clinical data and further inform care for CuTS patients. More studies are needed to corroborate further the correlations revealed herein.
Conflicts of Interest
No benefits in any form have been received or will be received related directly to this article.
Acknowledgments
We thank Samantha Hoffman for providing continued help with data acquisition and project initiation.
References
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