Abstract
Introduction There is a known false negative rate when using electrodiagnostic studies (EDS) to diagnose carpal tunnel syndrome (CTS). This can pose a management dilemma for patients with signs and symptoms that correlate with CTS but normal EDS. While corticosteroid injection into the carpal tunnel has been used in this setting for diagnostic purposes, there is little data in the literature supporting this practice. The purpose of this study is to evaluate the prognostic value of a carpal tunnel corticosteroid injection in patients with a normal electrodiagnostic study but exhibiting signs and symptoms suggestive of carpal tunnel, who proceed with a carpal tunnel release.
Materials and Methods The group included 34 patients presenting to an academic orthopedic practice over the years 2010 to 2019 who had negative EDS, a carpal tunnel corticosteroid injection, and a carpal tunnel release. One patient (2.9%), where the response to the corticosteroid injection was not documented, was excluded from the study, yielding a study cohort of 33 patients. Three patients had bilateral disease, yielding 36 hands for evaluation. Statistical analysis was performed using Chi-square analysis for nonparametric data.
Results Thirty-two hands (88.9%) demonstrated complete or partial relief of neuropathic symptoms after the corticosteroid injection, while four (11.1%) did not experience any improvement. Thirty-one hands (86.1%) had symptom improvement following surgery, compared with five (13.9%) which did not. Of the 32 hands that demonstrated relief following the injection, 29 hands (90.6%) improved after surgery. Of the four hands that did not demonstrate relief after the injection, two (50%) improved after surgery. This difference was statistically significant ( p = 0.03).
Conclusion Patients diagnosed with a high index of suspicion for CTS do well with operative intervention despite a normal electrodiagnostic test if they have had a positive response to a preoperative injection. The injection can provide reassurance to both the patient and surgeon before proceeding to surgery. Although patients with a normal electrodiagnostic test and no response to cortisone can still do well with surgical intervention, the surgeon should carefully review both the history and physical examination as surgical success may decrease when both diagnostic tests are negative. Performing a corticosteroid injection is an additional diagnostic tool to consider in the management of patients with CTS and normal electrodiagnostic testing.
Keywords: carpal tunnel syndrome, electrodiagnostic, cortisone injection, nerve conduction studies, electromyography
Introduction
Carpal tunnel syndrome (CTS) is the most common compression neuropathy of the upper extremity and one of the most common conditions seen in a hand surgery clinic. In addition to a careful history and physical examination, electrodiagnostic studies (EDS) in the form of nerve conduction studies (NCS) and electromyography (EMG) are often used in establishing the diagnosis. EDS have been shown to be useful in ascertaining the diagnosis of CTS with the ability to confirm a clinical diagnosis with a high degree of sensitivity and specificity. 1
Corticosteroid injections have also been found to be useful in both the diagnosis and treatment of CTS. 2 3 4 5 The primary mechanism of locally injected corticosteroids is through the altered action of cytokines involved in inflammation. This medication is thought to suppress the flexor tenosynovitis and decrease pressure in the carpal canal. An injection for mild-to-moderate disease may alleviate patient's symptoms, although there is a chance of recurrence. Patients who achieve relief of symptoms after a corticosteroid injection have a significantly better response to surgery than those who did not obtain relief from the injection. 5 A historic study did see a beneficial response to a corticosteroid injection, defined as greater than 50% relief of symptoms, and concluded corticosteroid injection to be an excellent diagnostic and prognostic tool. 6 Despite the aforementioned studies, there is very little documentation regarding the utility of corticosteroid injection in the diagnosis and treatment of CTS.
EDS can have false negative rates as high as 8 to 25%. 1 7 Utilizing patient response to corticosteroid injection as a prognostic factor for surgical outcome may be useful. 5 This may be of particular importance with patients who present with clinical symptoms consistent with CTS but are found to have normal EDS. The aim of this study was to determine the role of a diagnostic corticosteroid injection in patients who have signs and symptoms of CTS but also have no EDS evidence of median nerve neuropathy at the wrist. We hypothesized that patients diagnosed with CTS based on clinical examination and history, but having, normal EDS, and experiencing a beneficial response to a carpal tunnel cortisone injection would have better surgical outcomes than those who did not respond to an injection. Our secondary goal was to determine the predictive value of a cortisone injection in a clinically symptomatic patient with normal EDS.
Materials and Methods
After obtaining approval from the institutional review board of our institution, a review of medical records was completed for a 10-year period of 2010 to 2019. The medical record database was queried for patients with a current procedural terminology (CPT) code of 64721 or 29848 to determine who underwent carpal tunnel surgery. A total of 21,833 patients were identified. Within this group, those who were evaluated with an EDS (CPT codes 95860, 95900, and 95904) and undergone a corticosteroid injection into the carpal tunnel (CPT code 20526, injection of carpal tunnel) prior to the surgical procedure were identified. This search yielded a total of 757 patients.
These medical records were reviewed to determine the results of the EDS, whether the corticosteroid injection was given for diagnostic or therapeutic purposes, and the outcomes of the injection and surgical procedure. Patients who had a normal EDS, a carpal tunnel injection, and who were treated surgically included in the study. Of the 757 records, 34 patients met the inclusion criteria. One patient (2.9%), where the response to the corticosteroid injection was not documented, was excluded from the study, yielding a study cohort of 33 patients. Three patients had bilateral disease, yielding 36 hands for evaluation.
The results of surgery were qualitatively assessed. In addition, the Boston carpal tunnel questionnaire (BCTQ) was administered via phone at an average of 36 months (5–119 months) after surgery. 8 Up to three attempts were made to reach each patient. A total of 28 of the 33 patients were able to be contacted and the outcome form completed.
Statistical analysis included Chi-square analysis for nonparametric data, while the Student's t -test was employed for continuous variables.
Results
The presence of provocative maneuvers, response to cortisone injection, and surgical outcomes were tabulated for the 33 patients in the study group ( Table 1 ). There were 22 females and 11 males. The average age was 51 years at time of surgery.
Table 1. Patient data.
| Patient | Laterality | Injection result | Clinical exam | Surgery result/follow-up | BCTQ score |
|---|---|---|---|---|---|
| 1 | Left | No response (*) | pos Tinel's, pos Durkan's | Improvement in neurologic symptoms | 1.00 |
| 2 | Right | Some relief | neg Tinel's, pos Durkan's | Ring improved, continued burning in long | 2.26 |
| 3 | Right | 50% relief | neg Tinel's, pos Durkan's | No improvement (*) | 1.95 |
| 4 | Right | Some | pos Tinel's | No complaints | X |
| 5 | Left | Helped | pos Tinel's, pos Durkan's | Numbness resolved | 2.21 |
| 6 | Left | Significant | pos provocative tests | Improvement | 2.05 |
| 7 | Bilateral | Good relief | pos Tinel's, pos Durkan's | Resolved at 2 months | 1.63 |
| 8 | Left | Partial relief | pos Durkan's | Significant improvement | 2.74 |
| 9 | Right | Short-term relief | pos Tinel's, pos Durkan's, pos Phalen's | Excellent | 1.42 |
| 10 | Right | Good relief | pos provocative tests | Resolution at 6 months | 1.95 |
| 11 | Right | Worked great | equivocal Tinel's, pos Durkan's | Not improved (*) | 1.16 |
| 12 | Right | Substantial relief | pos Durkan's, pos Phalen's | Resolved at 1 month | 1.37 |
| 13 | Bilateral | Some relief | pos provocative tests | Improved | 1.37 |
| 14 | Left | Complete relief | pos Tinel's, pos Durkan's | Resolved | 1.16 |
| 15 | Bilateral | Good relief | pos Tinel's, pos Durkan's | Improved at 2 months | 1.00 |
| 16 | Right | No improvement (*) | neg Tinel's, pos Phalen's | No improvement at 1 year (*) | 1.00 |
| 17 | Left | Short-term relief | pos Tinel's, pos Phalen's | Doing well | 2.26 |
| 18 | Left | Some improvement | pos provocative tests | Improved at 12 days postoperation | X |
| 19 | Right | 90% short-term relief | pos Tinel's, pos Durkan's | Resolved at 11 weeks | 3.53 |
| 20 | Right | 80–90% relief | no provocative findings | Complete resolution | X |
| 21 | Right | Helped several months | pos Phalen's | Resolution 14 months | 1.42 |
| 22 | Right | Remains symptomatic (*) | pos provocative tests | No improvement (*) | 2.42 |
| 23 | Left | Significant, 75% better | pos Tinel's, equivocal Phalen's | Resolved 8 months | 1.32 |
| 24 | Right | Mild improvement | neg Tinel's, equivocal Durkan's | Significant improvement | 1.79 |
| 25 | Left | Complete relief | pos provocative tests | Resolved 3 months postoperation | X |
| 26 | Right | Improvement | not described | Numbness resolved | 1.42 |
| 27 | Left | No improvement (*) | pos Tinel's, pos Durkan's | Much improved | 1.53 |
| 28 | Right | Improvement | pos Tinel's, pos Durkan's | Significant improvement | 1.58 |
| 29 | Left | Excellent | pos provocative tests | No improvement, radicular symptoms (*) | 1.68 |
| 30 | Right | Helped | pos Tinel's, pos Durkan's | Very well | 1.00 |
| 31 | Right | Complete relief | pos Tinel's, pos Durkan's | Resolution then revision 2 years later | 2.42 |
| 32 | Right | Improved somewhat | pos provocative tests | Completely resolved | X |
| 33 | Right | Limited improvement | pos provocative tests | Significant improvement | 1.68 |
Abbreviation: BCTQ, Boston carpal tunnel questionnaire.
* = failure of treatment.X = unable to obtain.
The 32 hands (88.9%) in 29 patients demonstrated complete or partial relief of the neuropathic symptoms after the corticosteroid injection, while four (11.1%) did not experience any improvement. Of 32 hands (86.1%) in 28 patients had symptom improvement following surgery, compared with five (13.9%) which did not. Of the 32 hands that demonstrated relief following the injection, 29 hands (90.6%) improved after surgery. Of the four hands that did not demonstrate relief after the injection only two (50%) improved after surgery. This difference was statistically significant ( p = 0.03) ( Tables 2 and 3 ). The sensitivity, specificity, positive predictive value, and negative predictive value are listed in Table 3 .
Table 2. Outcomes of injection and surgery.
| Positive surgery | Negative surgery | Total | |
|---|---|---|---|
| Positive injection | 29 | 3 | 32 |
| Negative injection | 2 | 2 | 4 |
| Total | 31 | 35 | 36 |
Table 3. Study statistics.
| Statistic | Value | 95% CI |
|---|---|---|
| Sensitivity | 93.55% | 78.58–99.21% |
| Specificity | 40% | 5.27–85.34% |
| Positive predictive value | 90.63% | 82.45–95.21% |
| Negative predictive value | 50% | 15.22–84.78% |
Abbreviation: CI, confidence interval.
When comparing the patients that responded favorably to the corticosteroid injection to those who had no improvement, there was no difference in the BCTQ scores. Patients who improved with injection had an average BCTQ score of 1.8 (range: 1.0–3.5) and those who did not improve had a score of 1.5 (range: 1.0–2.4) ( p = 0.42) Additionally, comparison of the group that had relief after surgery to the group that did not improve after surgery showed no difference in BCTQ scores. Those who improved with surgery had an average BCTQ score of 1.7 (range: 1.0–3.5) and those that did not improve had a score of 1.6 (range: 1.0–2.4) ( p = 0.74).
Discussion
Currently, there is debate regarding the need to obtain EDS to accurately diagnose CTS. However, EDS have been shown to be useful in confirming the diagnosis of CTS with a high degree of sensitivity and specificity. 1 The nerve conduction measurements have historically been a valuable test for mild-to-moderate CTS. The underlying pathophysiology of focal demyelination of the median nerve secondary to compression results in measurable slowing of nerve conduction. 9 Although sensitivity is high, there remains a false negative rate with EDS when the measured outcome is relief of symptoms after surgery. Previous studies have shown that false negative rates with EDS can range from 8 to 25%. 1 7 This known false-negative rate must be factored into the management of patients with clinical symptoms consistent with CTS.
The American Academy of Orthopaedic Surgeons (AAOS) 2016 guidelines recognize that EDS has long been considered to represent a reference standard, but this assumption is untenable because these tests clearly have false positive and negative results. Beyond this, there is no consensus supporting any single diagnostic tool as a reference standard. 10 In the original AAOS guidelines for the management of CTS published in 2009, EDS were recommended as an option (“may obtain”) to differentiate between diagnoses, and were strongly recommended (“should obtain”) when surgical management was being considered. 11 Graham subsequently argued that addition of EDS to a symptom assigned clinical score utilizing CTS-6 did not increase the probability of diagnosis. 12 The CTS-6 is a list of six clinical criteria developed to guide diagnostic practices in CTS. CTS-6 is a validated diagnostic aid that utilizes clinical findings identified by patient history and clinical tests performed on physical examination to facilitate the probability of CTS with a high degree of accuracy. 13 The most current 2016 AAOS guidelines score EDS as moderate evidence, together with diagnostic questionnaires such as CTS-6, under the heading of “diagnostic scales.” The authors conclude that establishing consensus on a reference standard for the diagnosis for CTS is the most important research goal in this area. 14 15
When EDS are ordered, they typically include both NCS and a needle EMG. NCS have traditionally been found to be the more valuable than EMG, as they detect impaired median nerve conduction across the carpal tunnel, which may be an earlier finding in CTS. 9 An EDS study performed only at the wrist level will not exclude proximal nerve compression such as pronator syndrome or cervicobrachialgia. Needle EMG studies are to be used as a complement to the data obtained by the NCS. 16 EMG can detect denervation by the presence of membrane instability, evidenced by fibrillation potentials, positive sharp waves, and altered motor unit morphology. Typically, if EMG detects axonal loss of motor nerves and subsequent motor unit reorganization, this may be indicative of a severe case of CTS. 9 While needle EMG may have a potential role in ruling out other causes of symptomatology, determining severity of disease, and predicting postsurgical outcomes, it is not routinely needed as a staple in the diagnosis of CTS. 17 Also, needle EMG studies may cause undue pain to patients and have additional associated costs which are separate from payments for NCS. 18
Despite advances in the diagnosis of this condition, patients present almost daily to the hand surgery clinic with a copy of their EDS report ordered by a referring physician. For those patients presenting with a strong history and physical examination consistent with CTS but normal EDS, this typically leads to a lengthy discussion of treatment options. Patients may be skeptical to proceed with surgical intervention with a report that states “no evidence of carpal tunnel found.” Given the findings in our study, many of these test results may be “false negatives.” Performing a diagnostic injection may be a way to alleviate patients' fears of an invasive procedure in addition to providing temporary relief of neuropathic symptoms. This will build trust with the treating hand surgeon and, if successful, increase the probability of a successful surgical result.
Corticosteroid injections have been found to be useful in both the diagnosis and treatment of CTS, with a benefit that has been supported by multiple systematic reviews and randomized controlled trials. 2 3 4 5 There is existing data showing that patients with less severe stages of CTS, as measured by median nerve cross-sectional area, swelling ratio, and symptom severity scores, are more likely to respond favorably to cortisone injections. 19 In addition to relieving symptoms of CTS in the short term, corticosteroid injections may also reduce the rate of surgery in the long term. 3 Studies looking at long-term follow-up after injection found that corticosteroids may serve a therapeutic role in the management of CTS, particularly in patients with mild-to-moderate disease. In patients receiving a single primary corticosteroid injection, between 32 and 63% did not go on to receive any subsequent treatment, such as additional injections or surgery, at 5–7 year follow-up. 20 21 In our study, several different corticosteroids were used including triamcinolone, dexamethasone, and betamethasone.
Carpal tunnel corticosteroid injection may also serve as a prognostic indicator for CTS treatment. Patients who achieve relief of symptoms after a corticosteroid injection have a significantly better response to surgery than those who did not respond to the injection. One study reported that patients who had relief from a corticosteroid injection were cured with surgery 87% of the time while surgical success was only experienced in 54% of patients who did not achieve relief from injection. 5 Additional studies have also explored the diagnostic value of corticosteroid injections in CTS and found that a good response from corticosteroid injection, defined as greater than 50% relief of symptoms, is an excellent prognostic sign for better outcomes after subsequent surgery. 6 A prospective study by Miranda et al found that longer relief of symptoms after corticosteroid injection correlated with better results after surgical treatment. 22 Corticosteroid injections have also been studied for their role in predicting the outcome of revision carpal tunnel surgery. In patients with recurrent CTS, relief from corticosteroid injection as a diagnostic test for predicting successful revision surgery was found to have both a high sensitivity and positive predictive value, with values of 87% for both. 23
Only three patients who improved with a cortisone shot did not have long-term improvement with the operative procedure. Patient 3 was found to have thoracic outlet syndrome. Patient 11 had a very short-term relief with carpal tunnel decompression, but the pain and numbness quickly returned. It was though her symptoms were consistent with inflammatory arthritis and was sent to be evaluated by a rheumatologist. Patient 29 was found to have radicular symptoms and pathology in the cervical spine. This highlights the importance of a complete physical exam to look for other causes of hand numbness before proceeding with surgical intervention.
As this study is a retrospective review rather than a prospective trial, there are inherent limitations. It was not possible to control intervention outcome assessment in this study; instead, nonstudy personnel were relied upon for accurate record keeping from which our data were obtained. EDS were interpreted by the physician performing the test, not by members of the study team. We used the conclusion of their report to determine if an EDS was positive or negative. It would have been preferable to standardized parameters used to determine EDS test results. Due to our electronic medical record software, this study only included patients who had EDS done at our institution. Patients who had outside testing done were unable to be screened by CPT code and therefore could not be identified or included in this study. Due to the nature of the query of patients having an EDS, cortisone injection, and surgery, we do not have records on those patients who had a negative EDS, cortisone injection but did not have surgery. It is possible the injection helped with resolution of symptoms making surgery unnecessary.
Additional limitations include that this study utilized a dichotomous outcome for improvement after corticosteroid injection and surgery. Improvement exists on a continuum rather than as a binary outcome, and with differing thresholds at which improvement is defined, the results of the study may have been altered. The metrics of improvement after injection and after surgery were subjective patient reported outcomes as opposed to a standardized validated scale. Had this been a prospective study, more standardized assessments could have been used to document outcomes. Due to the high improvement rate after surgery, our group with failure to improve was very small.
The use of the BCTQ was completed to add additional data to our study. However, the duration between surgical intervention and questionnaire administration ranged from 5 to 119 months. Additional trauma, disease, recurrent neuropathy, or degeneration may have occurred to the operative hand during this extensive interval, which may alter patient's responses to the questionnaire. The BCTQ data may be of limited value due to this delay in administration.
Patients with a high index of suspicion for CTS do well with operative intervention despite a negative EDS. A positive response to a diagnostic carpal tunnel injection is associated with an increased chance of a successful surgical result for those patients with normal EDS. Although patients with a negative EDS and no response to cortisone can still do well with surgical intervention, an extensive and thorough patient discussion is warranted as we found that surgical success was decreased when both diagnostic tests were negative. Performing a diagnostic corticosteroid injection is an additional diagnostic tool to consider in the management of patients with suspected CTS, especially with positive clinical signs and negative EDS.
Footnotes
Conflict of Interest None declared.
References
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