Sonography and electrodiagnosis in carpal tunnel syndrome diagnosis, an analysis of the literature

Abstract

We read with interest the recent review article by Seror [ [1] Seror P. Sonography and electrodiagnosis in carpal tunnel syndrome diagnosis, an analysis of the literature. Eur J Radiol. 2008; 67: 146-152 Abstract Full Text Full Text PDF PubMed Scopus (83) Google Scholar ] coming from the Electromyography Laboratory in Paris, France, and published by the European Journal of Radiology. The author reviews the literature regarding ultrasound (US) in the diagnosis of carpal tunnel syndrome (CTS) and attempts comparison with electrodiagnostic studies (EDX). After a careful and meticulous review, the author concludes that “…. sonography appears of little use in the carpal tunnel syndrome itself”. We would like to share our concerns regarding some of the statements and conclusions of this paper. 1.It is stated in the discussion section that “Clearly, what is needed is a diagnostic sensitivity and specificity closer to 100%, more up-to-date and as close as possible to evidence-based medicine criteria.” However, there is no gold standard for the diagnosis of CTS. For example, in 1993 the American Association of Electrodiagnostic Medicine, American Academy of Neurology and American Academy of Physical Medicine and Rehabilitation, after an extensive review of the literature, reported in their combined summary statement that EDX studies had sensitivities ranging from 49% to 84% and specificities of 95% or greater [ [2] Practice parameter for electrodiagnostic studies in carpal tunnel syndrome: summary statement. American Association of Electrodiagnostic Medicine, American Academy of Neurology, American Academy of Physical Medicine and Rehabilitation. Muscle Nerve 1993;16:1390–1391. Google Scholar ]. Therefore, the evaluation of a new approach, other than EDX, for the diagnosis of CTS is justified. 2.The scientific progress in implementing a new diagnostic test is not straightforward when there is no gold standard for comparison. This difficult issue is not only specific to the application of US, but also to every other test for CTS, including EDX. Consequently, the US studies published to date, adopt different inclusion and exclusion criteria, and therefore, as correctly pointed out by the author, report variable results, regarding the sensitivity and specificity of US in the diagnosis of CTS. This also leads some authors to use receiver operating characteristic (ROC) curves to define the best sensitivity over specificity ratio and thus arbitrarily choose “optimal” cut-off points for the diagnosis. However, the vast majority of studies incontestably show that US is sensitive and specific for the diagnosis of CTS. The next step should be further standardization of the research; this might be accomplished for example by implementing similar and more specific inclusion/exclusion criteria across studies, and performing large scale blinded randomized studies in different clinical settings (primary versus tertiary care) to test the validity of US in the various situations encountered in clinical practice. Therefore, there are yet several challenges to be met in order to realize the full potential of US, and thus we disagree with the author's statement that “…. sonography appears of little use in the carpal tunnel syndrome itself”. 3.Regarding our study, by Wiesler et al. [ [3] Wiesler E.R. Chloros G.D. Cartwright M.S. Smith B.P. Rushing J. Walker F.O. The use of diagnostic ultrasound in carpal tunnel syndrome. J Hand Surg (Am). 2006; 31: 726-732 Abstract Full Text Full Text PDF PubMed Scopus (176) Google Scholar ]: •The author states that our study used “peculiar inclusion criteria”. The most strict definition of CTS includes the following: consistent history and clinical examination, consistent EDX, and improvement with surgery, which is why we chose that definition to ensure that all patients we included had CTS. We agree that improvement following surgery cannot be used as the sole diagnostic criterion as surgery is not always successful (incomplete release of the flexor retinaculum), or may have other complications. However, this is a limitation that again stems from the fact that there is absence of a gold standard for the diagnosis of CTS, as stated above. Our purpose was to make sure that all patients included in the study had confirmed CTS using the strictest criteria, and as stated above, we agree that more standardization of the criteria is the required next step in US research. •The author states that “the portability and safety of an EDX machine running on a laptop computer is strictly that of US”. However, this comparison statement in our study pertains to other imaging modalities, such as MRI, and not to EDX. We did not attempt comparison between US and EDX, and we do agree with the author that “there is no competition but rather complementary roles between sonography and EDX”. This is similar to the cardiologist that uses sonography and electrodiagnosis (electrocardiogram) to establish a diagnosis. 4.Regarding the study by Koyuncuoglu et al. [ [4] Koyuncuoglu H.R. Kutluhan S. Yesildag A. Oyar O. Guler K. Ozden A. The value of ultrasonographic measurement in carpal tunnel syndrome in patients with negative electrodiagnostic tests. Eur J Radiol. 2005; 56: 365-369 Abstract Full Text Full Text PDF PubMed Scopus (135) Google Scholar ], the author is correct when he reports that this study did not use the most sensitive EDX tests for CTS, because a prolonged median motor latency was required for the diagnosis of CTS. However, this diagnostic test may not be as poor as the author suggests, given that pooled data show a prolonged median motor latency has a sensitivity of 63% for the diagnosis of CTS [ [5] Practice parameter for electrodiagnostic studies in carpal tunnel syndrome: summary statement. Muscle Nerve. 2002;25:918–922. Google Scholar ]. In the study by Koyuncuoglu et al. [ [4] Koyuncuoglu H.R. Kutluhan S. Yesildag A. Oyar O. Guler K. Ozden A. The value of ultrasonographic measurement in carpal tunnel syndrome in patients with negative electrodiagnostic tests. Eur J Radiol. 2005; 56: 365-369 Abstract Full Text Full Text PDF PubMed Scopus (135) Google Scholar ] the authors were able to demonstrate an increase in median nerve CSA in those with clinical CTS and negative EDX, when compared to controls. To us, this indicates that the use of US in those with negative EDX is an area that deserves further exploration. 5.We agree with the author's statement in the conclusion section that: “one must keep in mind that the final aim of all examinations in CTS is to determine the cause(s) of upper limb paresthesiae, not simply if there is a median nerve lesion at wrist or not”. However, EDX is a measure of nerve fiber function and does not provide anatomic information; US has far more capabilities in establishing an anatomic diagnosis for the less common, non-idiopathic causes of CTS, for example, cysts, aberrant muscles and vessels, neuromas, etc. The author states that: “Sonography is an efficient morphological tool to search for a space-occupying mass such as a cyst, but this is rarely ever the case in the carpal tunnel”; we feel, however, that these cases may be overlooked when only EDX is used. Furthermore, the author states that: “Additionally, EDX can determine if the lesion is solitary or one of multiple lesions (mononeuropathy multiplex, multiple entrapment neuropathies), or a feature of a polyneuropathy (demyelinating neuropathy).” When evaluating CTS with US, it is possible to take cross-sectional area measurements more proximally to ensure that there is no generalized nerve swelling, as it occurs for example in Charcot–Marie Tooth. We also find US useful in individuals with a generalized polyneuropathy that may have superimposed CTS, which can be very difficult to assess with EDX alone. When using the two modalities in combination, the EDX studies show the generalized neuropathy and US shows focal swelling at the distal wrist crease. 6.In the results section of the manuscript, the author calculates “a theoretical EDX sensitivity from the experience of various neurophysiologists…”. The calculations are theoretical and the methodology is unclear; an appropriate way to address this issue would have been to conduct a true meta-analysis of the literature, but this would have entailed a complete redirecting, refocusing, of the manuscript, including specific methodology to carry out that investigation. 7.The author states that some patients have an anatomical variation with division of the median nerve into two or three parts at the inlet of the carpal tunnel (bifid median nerve), which precludes calculation of cross-sectional areas at this point. We agree with this observation, however, we disagree that this is a limitation of US. A bifid MN [ [6] Iannicelli E. Chianta G.A. Salvini V. Almberger M. Monacelli G. Passariello R. Evaluation of bifid median nerve with sonography and MR imaging. J Ultrasound Med. 2000; 19: 481-485 PubMed Google Scholar ], which may occur in 2.8% of cases [ [7] Lanz U. Anatomical variations of the median nerve in the carpal tunnel. J Hand Surg (Am). 1977; 2: 44-53 Abstract Full Text PDF PubMed Scopus (328) Google Scholar ], and in such cases, US may be valuable in modifying the treatment approach as the surgeon may decide in favor of an open approach instead of endoscopic carpal tunnel release to avoid injury to the median nerve branches. This is also valid in case of discovery, by US, of a persistent median artery [ [8] Gassner E.M. Schocke M. Peer S. Schwabegger A. Jaschke W. Bodner G. Persistent median artery in the carpal tunnel: color Doppler ultrasonographic findings. J Ultrasound Med. 2002; 21: 455-461 PubMed Google Scholar ]. 8.The author states that: “Using sonography for post-treatment follow-up of CTS does not appear suitable”, and includes the study by Lee et al. [ [9] Lee C.H. Kim T.K. Yoon E.S. Dhong E.S. Correlation of high-resolution ultrasonographic findings with the clinical symptoms and electrodiagnostic data in carpal tunnel syndrome. Ann Plast Surg. 2005; 54: 20-23 Crossref PubMed Scopus (79) Google Scholar ], that has several methodological shortcomings [ [10] Chloros G.D. Papadonikolakis A. Themistocleous G.S. Correlation of high-resolution ultrasonographic findings with the clinical symptoms and electrodiagnostic data in carpal tunnel syndrome. Ann Plast Surg. 2007; 59: 351-352 Crossref PubMed Scopus (3) Google Scholar ]. Recent studies show a significant decrease in median nerve cross-sectional area measured by US [ 11 Abicalaf C.A. de Barros N. Sernik R.A. et al. Ultrasound evaluation of patients with carpal tunnel syndrome before and after endoscopic release of the transverse carpal ligament. Clin Radiol. 2007; 62: 891-894 Abstract Full Text Full Text PDF PubMed Scopus (67) Google Scholar , 12 Colak A. Kutlay M. Pekkafali Z. et al. Use of sonography in carpal tunnel syndrome surgery. A prospective study. Neurol Med Chir (Tokyo). 2007; 47 (discussion 115): 109-115 Crossref PubMed Scopus (33) Google Scholar ], at 3 months and normalization of flattening ratio [ [13] El-Karabaty H. Hetzel A. Galla T.J. Horch R.E. Lucking C.H. Glocker F.X. The effect of carpal tunnel release on median nerve flattening and nerve conduction. Electromyogr Clin Neurophysiol. 2005; 45: 223-227 PubMed Google Scholar ] after 2 weeks following carpal tunnel release. Further investigation is warranted to determine the validity of those findings to confirm that surgery is successful. In addition, although more than 90% of CTS operations are successful, incomplete resection of the flexor retinaculum, leading to recurrence of symptoms is the commonest complication. US is able to document continuity of the intact distal portion of the retinaculum, which is the most frequent finding [ [14] Bianchi S. Montet X. Martinoli C. Bonvin F. Fasel J. High-resolution sonography of compressive neuropathies of the wrist. J Clin Ultrasound. 2004; 32: 451-461 Crossref PubMed Scopus (41) Google Scholar ]. Again, this could not be accomplished with EDX alone.