Examination of patients for carpal tunnel syndrome Sensibility, provocative, and motor testing

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Examination of patients for carpal tunnel syndrome Sensibility, provocative, and motor testing

Carl F. Palumbo, MD

^a

, Robert M. Szabo, MD, MPH

^b,

*

aThe Indiana Hand Center, 8501 Harcourt Road, Indianapolis, IN 46280, USA

bDepartment of Orthopaedic Surgery, Hand and Upper Extremity Service, University of California, Davis, School of Medicine, 4860 Y Street, Suite 3800, Sacramento, CA 95817, USA

Carpal tunnel syndrome (CTS) is the most common nerve entrapment syndrome diagnosed and affects 0.1% to 0.5% of the general population [1,2]. While a careful history may never establish the cause of the patient’s CTS, the history in combination with the physical examination in most cases at least leads to the correct diagnosis. In fact, in many hand surgery practices, a careful history and examination consistent with CTS is all that is needed to confirm the diagnosis. Even though CTS remains a clinical diagnosis, electrodiagnostic testing has replaced a careful physical exam in many practices. Some authors, observing that neu- rophysiological exams afford the only objective test of median nerve function, have concluded that CTS should be diagnosed solely on the basis of electrodiagnostic examinations [3,4]. A group of 12 medical researchers experienced in conducting epidemiologic studies on CTS could not reach consensus regarding diagnosis of subjects with classic symptoms of CTS with negative electrodiagnostic findings [5]. Also agreed on by consensus, a positive electrodiagnostic test with absent symptoms clearly cannot lead to the diagnosis of carpal tunnel syndrome [5]. Clinical history and physical examination including provocative tests are more easily performed than electrodiagnostic studies, and they are the most appropriate diagnostic tools in the ambulatory setting [6]. A self-administered hand diagram has also proven quite useful in evaluating patients for CTS [7].

Sensibility testing

Patients with CTS frequently present complain- ing of numbness and tingling in their fingers. A thorough sensory evaluation is warranted on the initial examination. Always perform the sensibility evaluation prior to provocative testing, as provocative tests may alter patients’ sensibility. By definition, objective sensory testing is not possible, because each test performed relies on the patient’s cooperation, subjective understanding, and response to the particular test performed. Never- theless, the most common tests utilized to evaluate sensibility are static or moving two-point discrimination, Semmes-Weinstein monofilament testing, and vibrometry. Understanding the nerve fiber- receptor systems and their role in sensation is nec- essary to appreciate what is actually being tested by the various sensibility tests.

The sensation of touch is mediated through two separate populations of large myelinated nerve ﬁbers, generically called the ‘‘quickly adapting’’

and the ‘‘slowly adapting’’ ﬁber-receptor systems.

Slowly adapting ﬁbers mediate the sensation of constant touch and pressure, whereas quickly adapting ﬁbers mediate the sensation of transient touch or movement [8–10]. Sensibility testing is conceptually divided into innervation density testing and threshold testing. Static and moving two- point discrimination are innervation density tests.

Static two-point discrimination measures slowly adapting fiber-receptors whereas moving two- point discrimination measures quickly adapting fibers. Innervation density tests measure the innervation of multiple overlapping peripheral receptor fields and are dependent on the cortical integration

* Corresponding author.

E-mail address:[email protected] (R.M. Szabo).

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of peripheral impulses [11]. Because a stimulus may be perceived normally in the presence of even a few intact peripheral ﬁbers, mild or even moderate compression of a peripheral nerve may not produce any alteration in an innervation density test.

Threshold tests, such as Semmes-Weinstein monofilaments and vibrometry, evaluate single nerve fibers innervating a single receptor or group of receptor cells [11]. Threshold testing is more likely to show a gradual and progressive change in value as more and more nerve fibers are affected, as in nerve compression. Threshold testing is the preferred method for evaluating the sensibility of the hand in CTS. Whereas the vibrometer is slightly more sensitive than monofilament testing in evaluating the sensibility of the hand, the nylon monofilaments are more user-friendly and more often employed [12].

Two-point discrimination

In 1958 Moberg first popularized the two-point discrimination test as an objective means for determining sensibility in the hand [13]. Static two- point discrimination is determined by placing two points of a caliper longitudinally against the skin until blanching occurs and by then asking the patient whether he or she feels one or two points (Fig. 1). The smallest distance in which two of three attempts are correctly identified is recorded in millimeters. This test detects constant touch and is a reflection of the slowly adapting nerve fibers. Normal two-point discrimination is

less than 6 mm. Moving two-point discrimination is determined by slowly moving the two points longitudinally along the ﬁnger pulp from proximal to distal. The smallest distance detected is recorded in millimeters. Normal moving two-point discrimination is less than 3 mm and is age dependent [14].

The fact that humans can discriminate two points that are closer together while moving compared to stationary does not mean that moving is more sensitive than static two-point discrimination in discriminating abnormalities. Moving two-point discrimination is also an innervation density test and the moving component reﬂects testing of the quickly adapting ﬁbers.

An abnormal two-point or moving two-point discrimination test in the presence of CTS indicates severe nerve compression. Several authors have determined that two-point discrimination values are normal in mild to moderate nerve compression syndromes [11,15–17].

Semmes-Weinstein monoﬁlaments

Semmes-Weinstein monofilaments were derived from the Von Frey hairs that were introduced in 1898 to measure pressure sensibility of the skin [18]. A thorn glued on to the end of a hair was pressed against the skin until the hair started to bow. Weinstein reintroduced this same idea in 1962, with nylon monofilaments replacing the Von Frey hairs [19]. The nylon monofilaments are applied perpendicular to the skin using enough pressure to bend the monofilament (Fig. 2). This

Fig. 1. The Weber two-point discrimination test is performed using a caliper or paper clip. Pressure is applied longitudinally against the pulp of the digit until skin blanching occurs. The distance between the two points is then recorded. Normal two-point discrimination is less than 6 mm.

Fig. 2. Semmes-Weinstein monofilament testing is performed by applying the nylon monofilament perpendicular to the pulp of the digit. Enough pressure is applied to bow the monofilament. The lowest value of the monofilament that the patient can perceive, with eyes closed, is recorded.

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test determines the threshold of slowly adapting nerve fibers. The monofilament kit (Gillis W. Long Hansens Disease Center, Carville, LA, USA) con- sists of five nylon monofilaments to mark five selected thresholds: 2.83 (normal), 3.61 (diminished light touch), 4.31 (diminished protective sensation), 4.56 (loss of protective sensation), and 6.65 (loss of deep pressure sensation). The numeric value represents the logarithm of 10 times the force in milligrams required to bow the monofilament [20]. The monofilament is applied three times to each digit and to the palm: a patient’s affirmative response to one or more of the monofilament appli- cations indicates that the stimulus is perceived. An abnormal result is due to the inability, with eyes closed, to determine any value greater than 2.83.

The sensitivities and specificities of monofilament testing vary in the literature. The sensitivity of Semmes-Weinstein monofilament testing may be as high as 91%, and specificity as high as 80%

[21]. Combining this test with the Phalen’s test may have a specificity of 86% [16]. Szabo et al determined the sensitivity and specificity of monofilament testing to be 65% and 42%, respectively.

Sensitivity improves to 83% if the sensibility testing is performed following a gravity-assisted wrist ﬂexed position (Phalen’s test) for 5 minutes [6].

Discrepancies in studies examining tests for CTS exist in part because of the diﬀerent nature of the populations being tested particularly with refer- ence to those selected as the control group [6].

Vibratory sensibility

The perception of vibratory stimuli is mediated through the same neural pathways as moving touch; that is, the quickly adapting nerve ﬁbers, but one, tests vibratory thresholds, while the other tests innervation density. A hypersensitive response to vibratory stimulation using a 256-cycles/sec tuning fork was introduced by Dellon [22] as a method of evaluating sensibility in both peripheral nerve injury and compression (Fig. 3). There are some practical problems with the tuning fork as a means of evaluating vibratory perception. The results cannot be expressed quantitatively and the stimulus amplitude is not precisely controlled; rather it varies with how forcefully the tuning fork is struck.

A calibrated vibrometer resolves these issues [12].

The vibrometer illustrated (BioThesiometer, Bio- Medical Instrument Co., Newbury, OH, USA) to determine vibratory sensibility in the hand has a ﬁxed frequency (120 Hz) but variable amplitude [23]. The vibrating head is held in contact with

the patient’s ﬁngertip while the stimulus intensity is slowly increased (Fig. 4). The voltage required to deliver one perceived stimulus is the threshold.

This test determines the threshold of quickly adapting nerve fibers. A calibration chart, pro- vided with the vibrometer, is then used to convert the voltage to microns of displacement [12]. The sensitivity of this test has been reported as high Fig. 3. Vibratory sensibility tested with a 256-c/s tuning fork. The tuning fork is struck against a firm object, after which the tuning fork’s prong is placed tangentially on the fingertip. Each digit is compared to the contralateral hand. Perception is considered abnormal when the patient states that the two stimuli feel different and can qualify the difference as being lesser or greater or some similar response.

Fig. 4. Vibratory sensibility utilizes a vibrometer with a ﬁxed frequency (120 Hz) and variable amplitude. The vibrating head is held in contact with the patient’s ﬁngertip while the stimulus intensity is slowly increased.

The voltage required to generate a perceived stimulus is converted to microns of displacement and recorded as the vibratory threshold.

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as 100% [24] and as low as 4% [25], with a speciﬁc- ity ranging from 83% [24] to 94% [25]. As larger, expensive, and more elaborate equipment was developed for assessing vibratory thresholds, the technique lost popularity in the clinical setting.

Almost equivalent information about sensibility in CTS can be learned from the Semmes-Weinstein monoﬁlament exam.

Provocative testing

Many provocative tests have been described to assist in the diagnosis of CTS. All are based on stressing an already compromised median nerve in order to exacerbate the symptoms of numbness, pain, and parasthesias. The three most commonly employed provocative tests are the wrist-ﬂexion test (Phalen’s test), the median nerve percussion test (Tinel’s test), and the median nerve compression test. The tourniquet test [26], also a provocative test, is seldom used because of its high false-positive rate [21].

Phalen’s test

One of the most universally utilized tests is the wrist-ﬂexion test introduced by Phalen in 1951 [27,28]. This test was originally performed by hold- ing the forearms upright, with the elbows resting on the examination table. The wrists were allowed to drop into ﬂexion with the assistance of gravity for 30 to 60 seconds (Fig. 5). The test is better per-

formed by eliminating elbow flexion that can produce symptoms in the little finger because of compression of the ulnar nerve at the cubital tunnel. Numbness or tingling in the median nerve distribution is considered a positive test. In this position, it is believed that the median nerve is compressed between the proximal edge of the transverse carpal ligament and the underlying flexor tendons and radius [28]. This test is less useful if there is limited wrist motion, or in cases of severe compression of the median nerve. Wrist extension narrows the carpal canal and increases the pressure within the carpal canal more than wrist flexion. This position can also exacerbate CTS symptoms and forms the basis of another provocative test, the reverse Phalen’s maneuver [29]. Phalen reported that between 74% and 80%

of his patients with CTS had positive wrist-flexion tests [27,28]; however, part of his faith in diagnosing CTS was based on a positive response to this test. Currently there is wide variation in the literature with regard to the reported sensitivity and specificity of Phalen’s test for detecting CTS. The sensitivity has ranged from as low as 10% [30] to as high as 88% [31], whereas the specificity has ranged from 47% [1] to 100% [31].

Nerve percussion test

Tinel’s sign, or the median nerve percussion test, is performed by gently tapping along the median nerve at the wrist from proximal to distal (Fig. 6). A positive response is recorded if the patient perceives tingling in the median nerve distribution. The examiner must perform this test gently because the use of too much force can produce parasthesias in a normal, healthy median nerve. Phalen reported 60% to 73% of his patients having a Tinel’s sign present [27,28]. Once again, there is a wide range of sensitivity and speciﬁcity reported in the literature. The sensitivity ranges from 26% [30] to 79% [32], and the speciﬁcity ranges from 40% [3] to 100% [31].

Nerve compression tests

Lundborg [33] ﬁrst showed us that sustained, experimentally applied external compression over the carpal canal could produce sensory changes in the median nerve distribution in normal subjects. The same principles are used in the carpal compression test. Whereas Paley and Durkan [34–36]

have popularized this test in the United States, credit belongs to Jungo, who ﬁrst described it in 1969 [37,38]. To perform this test, the examiner Fig. 5. Phalen’s wrist ﬂexion test is performed by having

the patient hold his or her forearms upright and having the patient rest his or her elbows on the examination table. The wrists are allowed to drop into ﬂexion with the assistance of gravity only. The test is considered positive if numbness or tingling is experienced in the median nerve distribution within 30 to 60 seconds.

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applies gentle sustained pressure with his or her thumb over the carpal canal (Fig. 7). Parasthesias in the median nerve distribution, which disappear when the pressure is relieved, within 30 seconds is

considered a positive test. Durkan developed and tested an instrumented device to perform this same test [34,35]. A calibrated gauge (Gorge Medical, Hood River, OR, USA) (Fig. 8) is used to place a more constant and precise degree of pressure over the carpal tunnel. After 15 seconds to 2 minutes the patient with CTS will usually complain of pain and/or parasthesias. One major advantage of the nerve compression test compared to the wrist-flexion test is that it can be performed with the wrist in the neutral position, making it of particular value in those wrists with limited motion. Using manual pressure, Durkan reported a sensitivity of 87% and a specificity of 90%. The sensitivity and specificity improved to 89% and 96%, respectively, when he used an instrumented carpal compression device.

The tourniquet test is another test occasionally used in the diagnosis of CTS [26]. A blood pressure cuﬀ is placed on the arm and inﬂated to a pressure above the systolic blood pressure for 60 seconds.

Pain and parasthesisas in the median nerve distribution distal to the wrist are suggestive of

Fig. 6. The median nerve percussion (Tinel’s test) test is performed by gently tapping along the median nerve from proximal to distal. A positive response is recorded if the patient perceives tingling in the median nerve distribution.

Fig. 7. The median nerve compression test is performed by applying gentle sustained pressure, with one’s thumb, over the carpal canal. Parasthesias in the median nerve distribution within 30 seconds that are relieved after removal of compression is considered a positive test.

Fig. 8. The Durkan’s test can also be performed with the use of a calibrated device. This device can apply consistent amount of pressure (13–14 psi) to the palm over the transverse carpal ligament. A positive test is similar to manual pressure.

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CTS. However, this test has proven of too little value because of its extremely high false-positive rate [21].

Hand diagram

The hand diagram has been used since the mid- 1980s and was modeled after a similar tool used in the evaluation of back pain. Patients are asked to shade on a diagram of a hand the areas of hand pain/parasthesias, and then asked to indicate the quality of their symptoms. The diagrams are then rated using the following classification system: a classic ratingis given to those patients with tingling, numbness, or decreased sensation with or without pain in at least two of digits 1 (thumb), 2 (index finger), or 3 (long finger). The palm and dorsum of the hand are excluded while wrist or pain radiating proximal to the wrist is recorded.

Aprobable ratingis described as the same for the classic rating, with the exception that palmar symptoms are allowed unless confined solely to the ulnar aspect of the hand. A possible rating involves tingling, numbness, or decreased sensation and/or pain in at least one of digits 1, 2, or 3. Finally, anunlikely ratingis given to the patients with no symptoms in digits 1, 2, or 3 [7]. Katz et al reported a sensitivity of 80% and a specificity of 90% using this method. However, others have found the sensitivity and specificity of the hand diagram to be much lower [39].

Motor testing

A careful assessment of the recurrent motor branch of the median nerve is essential in evaluating a patient suspected of having CTS. Prior to examining for muscle strength, one should observe for thenar muscle atrophy. This atrophy usually occurs late but often can be diﬃcult to detect. Pha- len points out that the easiest way to appreciate thenar atrophy is to compare the proﬁles of both thenar eminences (Fig. 9). Next, the strength of the abductor pollicis brevis muscle should be checked. In order to accurately check the strength of this muscle, resistance to palmar abduction as well as resistance to thumb supination should be evaluated (Fig. 10). Calibrated devices have been developed to more accurately check abductor pollicis brevis muscle strength [40] and are probably of most use in the research setting.

The history of symptoms, coupled with the physical examination, should form the basis for diagnosing CTS. Yet, there exists a wide range of sensitivity and speciﬁcity in most of the tests used

to make this diagnosis. Although electrodiagnostic testing has become the benchmark for validity testing in CTS, no true gold standard for the diagnosis of CTS exists [6,41]. However, the diagnostic accuracy of most of the physical exam tests for CTS rely on electrodiagnostic studies as the gold standard. This in itself leads to a diagnostic bias. There are many reasons that explain the large variability reported in the literature regarding the various tests’ accuracy. First, the criteria selected for the electrodiagnostic diagnosis of CTS are different among different clinicians. Second, there are differ- ences in the methods of performing the physical examination tests. In addition, the selection of Fig. 9. Thenar atrophy (left hand) is best appreciated if you simultaneously compare the profiles of both thenar eminences.

Fig. 10. Motor testing of the abductor pollicis brevis is shown. With the thumb placed in maximum palmar abduction, the patient is asked to resist the examiner’s applied downward pressure with one hand. The examiner palpates for contraction of the abductor pollicis brevis with the other hand.

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Table1 Diagnostictestsforcarpaltunnelsyndrome TestnameHowtoperformConditionmeasuredPositiveresultsInterpretationa Wristﬂexion(Phalens’s)testPlaceelbowsontable (extended),forearmsupright, wristsﬂexed Parasthesiasinresponse towristpositionTinglinginmediannerve distributionwithin 60seconds

HighprobabilityofCTS; sensitivity¼75%; speciﬁcity¼62% Percussion(Tinel’s)testGentlytapalongmediannerve atthewristSiteofnervelesionTinglinginmediannerve distributionProbableCTS; sensitivity¼64%; speciﬁcity¼71% Mediannervecompression (Durkan’s)testGentle,sustainedthumb pressureoverthecarpal tunnel

Parasthesiasinresponse toexternalpressureParasthesiaswithin30seconds thatdisappearafter removingpressure HighprobabilityofCTS; sensitivity¼89%; specificity¼45% TourniquettestBloodpressurecuffinflated toabovesystolicpressure for60seconds

Parasthesiasinresponse toischemiaTinglinginmediannerve distributionHighfalse-positiverate HanddiagramPatientmarksareasofpain/ numbnessonhanddiagramPatient’sperception ofsiteofnervedeficitAreamarkedwithinthe distributionofthemedian nerve ProbableCTS; sensitivity¼76%; specificity¼76% Thresholdtesting:Semmes- WeinsteinmonofilamentsTouchpulpofdigitwithnylon monofilamentofincreasing thicknessuntilitbows

Thresholdofslowlyadapting ﬁbersInabilitytodetecta2.83orless monoﬁlamentinmedian nervedistribution

ProbableCTS; sensitivity¼65%; speciﬁcity¼42% Thresholdtesting:vibrometryTouchpulpofdigitinmedian andulnarnervedistributions withvibratingprobe (120Hz)

Thresholdofquicklyadapting fibersAsymmetrybetweenmedian andulnarnervesHighprobabilityofdetecting CTS;sensitivity¼87%; specificityunknown Innervationdensitytesting: statictwo-pointTouchpulpofdigitwithtwo pointssetatknowndistanceInnervationdensityofslowly adaptingfibersUnabletodiscriminatetwo pointslessthan6mmapartAdvancedmediannerve dysfunction Innervationdensitytesting: movingtwo-pointSameasabove,withtwopoints movingalonglongitudinal axisoffingerpulp Innervationdensityofquickly adaptingfibersUnabletodiscriminatetwo pointslessthan3mmapartAdvancedmediannerve dysfunction a AllvaluesadaptedfromSzaboRM,SlaterJr.RR,FarverTB,StantonDB,SharmanWK.Thevalueofdiagnostictestingincarpaltunnelsyndrome.JHandSurg 1999;24A:704–14.

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patients diﬀers tremendously from one study to the next. Finally, the use of asymptomatic control subjects in determining the sensitivity and speciﬁcity of a diagnostic test leads to ‘‘spectrum bias’’ [42].

In the words of Gerr and Letz: ‘‘The true utility of a clinical test is not whether it can distinguish those for whom the diagnosis would never be entertained from those who have a clinical presentation that is typical for the disorder. Instead, diagnostic tests are used to assist in identifying those with the condition from among a population of patients with symptoms compatible with the condition, some of who actually have it and some of who do not’’ [43].

Szabo et al [6] ascertained the value of diagnostic testing in CTS by comparing three groups: group I had definite CTS as defined by history, clinical presentation, and improvement of symptoms following carpal tunnel release; group II had a variety of nontraumatic upper extremity disorders other than CTS; and group III subjects were asymptomatic healthy volunteers. Three sets of data were generated. The sensitivity and specificity of all tests were determined first using only the data from groups I and II. This set of data was subject to the highest degree of spectrum bias. The data were then analyzed to include group II subjects. A third set of data was then analyzed comparing only groups I and III that closely replicates the patient population presenting to a hand surgeon’s practice. This last set of data minimizes the effect of spectrum bias and provides more realistic sensitivity and specificity for physical examination tests for CTS. This last set of data seems more represen- tative of what one might expect in a hand surgeon’s practice (Table 1).

The value of a test for CTS depends on the pur- pose of performing the test. When screening a large population with a low prevalence for CTS, a test with a high sensitivity is needed so that no possible case goes undetected. However, in order to establish a diagnosis, a more speciﬁc test is required. Using a combination of physical examination techniques, including sensibility and provocative testing, the probability of correctly diagnosing CTS without relying on electrodiagnostic studies can be very high. Because CTS is a clinical syndrome, the diagnosis should be made on clinical grounds Electrodiagnosis is extremely important, however, in its ability to objectively document median nerve slowing and eliminate other competing diﬀerential diagnoses.

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