In the Sept. 3, 2014 issue of The Journal Fowler et al. elegantly compare the accuracy of ultrasound for confirming the clinical diagnosis of carpal tunnel syndrome with the current standard of electrodiagnostic testing. In a very well-designed trial using the validated CTS-6 patient-reported outcome tool as the reference standard, they determined 90% diagnostic specificity and 89% sensitivity for ultrasound, with a corresponding 80% specificity and 89% sensitivity for electrodiagnostic testing. In this experimental design, high-volume practitioners administered the diagnostic tests so there is a caveat: the reliability of both ultrasound and electrodiagnostic testing is probably dependent on practitioner experience.
The study clearly shows that in patients with positive CTS-6 results and no signs of radiculopathy or polyneuropathy, ultrasound is as good as electrodiagnostic testing at confirming the diagnosis–and more comfortable for the patient. But the findings also beg a question: Do we really need any adjunctive testing for this group of patients, who I think represent the majority of those presenting with carpal tunnel syndrome symptoms? Wouldn’t the patient-reported symptoms and physical-exam results that are captured in the CTS-6 be sufficient?
I believe most of us agree that a careful history and physical exam should always form the basis for most diagnoses in orthopaedics. Carpal tunnel syndrome has a well-clarified anatomic basis and a very effective surgical treatment. There may occasionally be a role for conservative care but it is often ineffective, and patients should be counseled carefully about the limited efficacy of splints and corticosteroid injections. For most patients in whom this diagnosis is strongly suggested by history and exam, advanced testing is not needed and only adds to patient and system costs. By ordering these tests only for complex cases in which the diagnosis or severity of impairment is unclear, we will be improving patient outcomes while lowering the overall cost of care. That in turn will help us achieve the “triple aim” of access, good outcomes, and lower cost.
As the volume of literature in the research of orthopaedic-related topics increase exponentially, there is increasingly a propensity of readers to rely on authors to be accurate not just in their statistical analysis and conclusion in their own studies, but also quotation and interpretation of results of other studies referenced in their featured article.
In the case of Fowler et al (ref 1), it is with some irony that the basis of validation of their mode of investigation (ie Ultrasound measurement of the cross-sectional area of the median nerve at the carpal tunnel inlet) is validated by CTS-6.
CTS-6 is a clinical tool developed by Graham et al (ref 2) to define a set of diagnostic criteria using certain key aspect of clinical history and examination of patients with suspected carpal tunnel syndrome, ranked in order of diagnostic importance using Delphi as a method of establishing consensus among a panel of expert clinicians, and then ‘ validated’ by another expert panel consensus. Graham then assessed the tool with reference to diagnostic electrophysiological studies (specifically median nerve conduction studies) (ref 3) and found that “for the majority of patients who are considered to have carpal tunnel syndrome on the basis of their history and physical examination alone, electrodiagnostic tests do not change the probability of diagnosing this condition to an extent that is clinically relevant”. The authors did NOT define CTS-6 >/= 12 to be considered a positive diagnosis for carpal tunnel syndrome
and <12 was considered a negative diagnosis; the actual statement was only to translate the likelihood found in the logistic regression model into a somewhat more clinically useful tool, for example CTS-6 score of 12 corresponded to a probability of carpal tunnel syndrome of approximately
0.80 (they did not actually claim the probability of 0.80 as a positive diagnosis for CTS).
It is therefore doubtful how an ultrasound assessment of median nerve at carpal tunnel inlet (US) can contribute more to a diagnosis of CTS, since the validation process in Fowler et al's study is bench-marked against an tool which is based on expert-panel consensus. Ultimately the only conclusion is that CTS is still predominantly a clinical diagnosis and should remain so, and that US offers no cheaper or better diagnostic alternative than a good clinical history taking and examination.
I do however organise nerve conduction studies of the upper limb in the following clinical scenarios:
a. when symptoms and clinical examination include more than just median nerve impingment at the level of carpal tunnel, ie when median nerve symptoms are more extensive (double crush), or when ulnar nerve may be affected
b. conditions involving bilateral wrists (in consideration of cervical pathology)
c. clinical evidence of Abductor Pollicis Brevis atrophy (for medicolegal reasons)
It is, of course, not uncommon in cases of both median and ulnar sensory symptoms, an open carpal tunnel release will both relieve symptoms of both nerves as the division of transverse carpal ligament will stop the impingement of median nerve by this ligament and also relax the Guyon canal thereby putting less pressure on the ulnar nerve (ref 4).
References
1. Fowler JR, Munsch M, Tosti R, Hagberg WC, Imbriglia JE. Comparison of ultrasound and electrodiagnostic testing for diagnosis of carpal tunnel syndrome: study using a validated clinical tool as the reference standard. J Bone Joint Surg Am. 2014 Sep 3;96(17):e148.
2. Graham B, Regehr G, Naglie G, Wright JG. Development and validation of
diagnostic criteria for carpal tunnel syndrome. J Hand Surg [Am]. 2006;31:
919-24.
3. Graham B. The value added by electrodiagnostic testing in the diagnosis of carpal tunnel syndrome. J Bone Joint Surg Am. 2008 Dec;90(12):2587-93.
4. Ablove RH1, Moy OJ, Peimer CA, Wheeler DR, Diao E.J. Pressure changes in Guyon's canal after carpal tunnel release. Hand Surg Br. 1996 Oct; 21(5):664-5.
I find a pre-operative EMG/NCV extremely helpful in the post-operative patient who has not responded to carpal tunnel release as well as I had anticipated (especially in the worker’s comp population and those with signs of severe carpal tunnel syndrome). A follow up EMG/NCV six months post op in these unhappy patients showing improvement in nerve function is paramount in their management. I obtain electrodiagnostic studies on all suspected peripheral neuropathy patients and I hope to continue to do so as long as the insurance companies will allow me to do so. Editorials like this will only give them ammunition to deny and delay.
I agree with just about everything Dr. Goh says, with one exception and that is the issue of expert consensus functioning as a reference standard. For conditions like CTS where there is no pathognomonic histologic or other pathology finding, expert consensus is really the only reference standard possible. It is understood that the nature of this reference standard could change through time as more knowledge about the condition is gained but this is still a viable tool to use in exactly the way in which Dr. Fowler used it in this study. The cut off or a score of 12 — representing an 80% probability was suggested as reasonable but that threshold could be adjusted according to the circumstance. For example, in working with a compensation population the threshold for suggesting treatment might have to be higher especially if the treatment being contemplated is surgery. This is one of the fundamental values of considering the diagnosis as a probability.