INTRODUCTION

 

Carpal tunnel syndrome is the most common entrapment syndrome of the upper extremities with an estimated incidence in the general community of 125/100,000/year. Typically, the dominant hand is affected first. The clinical hallmark and usual presenting feature of CTS is a pain syndrome called brachialgia paresthetica nocturna. It arises from compression of the median nerve in the canal formed by the transverse carpal ligament and carpal bones. Under pathological circumstances tissue pressure in the carpal tunnel reaches 30 mmHg, in other words; four times the normal level. Chronic or recurrent compression of the median nerve causes focal demyelination and eventually axon degeneration. Temporary ischemia due to compression of the vasa nervorum accounts for the reversible pain manifesting during the night¹.

In most instances, the diagnosis of CTS is reliably settled by an experienced clinician based on the patient’s history and a careful neurological examination including Phalen’s maneuver and Tinel’s sign².

 

Electro-diagnostic Studies (EDS) are recommended when median nerve compression causes significant discomfort or sustained sensorimotor deficits. An electrophysiological work-up is particularly useful to assess the damage to the median nerve (demyelination versus axon loss) relevant to therapeutic decisions, to rule out differential diagnoses or coexistent disease and to confirm the presence of CTS in the event of atypical complaints, pure motor deficits and prominent neuropathy. Various diagnostic criteria have been suggested including prolonged motor and sensory latencies of the median nerve and reduced sensory and motor conduction velocities. The optimal diagnostic criteria however remain uncertain³.  False negative and false positives can occur even when the most sensitive methods of EDS are used. Inadequacies of EDS have been partly blamed on a lack of standardized diagnostic criteria with reports of 16–34% of clinically defined CTS being missed with EDS, and sensitivities ranging from 49 to 84% considering this, blanket referrals for EDS are an expensive and inefficient approach to the diagnosis of CTS and may lead to continued diagnostic uncertainty⁴.

Magnetic Resonance Imaging provides anatomical information so; it is probable that the future of imaging will be in a supplementary role to the already established EDS in cases where anatomical clarification is required or where the results of EDS are equivocal. With the increased popularity of endoscopic procedures for CTS, it is becoming increasingly necessary to establish the underlying anatomy in order to prevent potential damage to the median nerve in cases where the anatomy is abnormal. Rare pathological causes of CTS such as ganglion, hemangioma or bony deformity are more likely to be uncovered with imaging modalities, and their presence may alter planned surgical intervention⁴.

Sonography is able to reliably diagnose idiopathic CTS in a high percentage of patients and rule out secondary CTS due to abnormalities inside the carpal tunnel such as flexor tendon synovitis, tumors or ganglia. If no abnormalities are found within the carpal tunnel, sonographic nerve inspection should be extended proximally upwards to the brachial plexus to exclude other rare and unusual abnormalities. Recent reports suggest that sonography should be performed as a first-line investigation after clinical examinations since the diagnostic value of sonographic findings are better than physical maneuvers. Other authors have shown that sonography has similar diagnostic values compared to electrodiagnostic studies. Only one report found sonography not accurate enough to replace electroneurographic testing⁵. In the present study we aimed at comparing the diagnostic accuracy of various tests used in the diagnosis of CTS and to determine the properties of the most accurate one.

 

PATIENTS AND METHODS

 

Fifty two cases of clinically established unilateral CTS were subjected to three different investigation modalities before surgical intervention (EDS, MRI and U/S). All patients underwent the open surgical technique for flexor carpal ligament release. The same surgical technique, however by different surgeons, was used in all operated cases.

The diagnosis of CTS was made according to American Academy of Neurology criteria, which include clinical history and symptoms. According to the hand diagram by Katz et al modified by consensus criteria of the classification of CTS⁶, only patients with paresthesia or pain in at least 2 of the first 3 fingers (classic/probable cases) were included in the study. Physical examination consisted of evaluating muscular strength and trophism, sensory function, and provocative clinical tests (Phalen’s and Tinel’s signs).

For this study, only patients with mild CTS were enrolled; mild cases were defined as those patients who reported only symptoms without objective motor deficit of thenar eminence muscles and normal objective sensory function in the median nerve territory of the hand. The mild cases belonged to stages 1 (nocturnal symptoms and morning symptoms on awakening) and 2 (diurnal symptoms) of a validated historical-objective clinical severity scale⁷.

The diagnostic electrophysiological criteria were: For distal motor latency the cutoff values used in different studies have ranged from 3.8 ms to 4.6 ms; however an intermediate value (4.2 ms) was considered as a cutoff point in this study.

The diagnostic MRI criteria were: 1. Swelling of the median nerve, 2. Increased signal intensity on T2-weighted images, and 3. Palmar bowing of the transverse carpal ligament. The usefulness of median nerve flattening remains controversial with some papers suggesting that flattening is a positive indicator of CTS, and others advising that CTS was more likely in patients who showed no median nerve flattening⁸.

The diagnostic sonographic criteria were: 1. Enlargement of the median nerve at the proximal carpal tunnel with an increased cross sectional area over 12 mm². 2. Changes in median nerve echotexture consistent with edema (loss of fascicular discrimination with more or less homogeneous hypoechoic appearance, and indistinct outer margins). 3. Abrupt caliber change (notch sign) at the proximal margin of the flexor retinaculum. 4. Detection of a large PMA (persistent median artery) or increased intraneural and perineural vascularity. 5. Dynamic scanning for detection of additional fluid or accessory muscle bellies. 6. Palmer bowing and thickening of the flexor retinaculum. A reliable documentation of this finding, however, will only be achieved with the application of high frequency sonographic transducers, which allow exact discrimination of the retinaculum. A cut-off value of > 4 mm between the most anterior part of the carpal ligament and the base line between the hamatum and trapezium has been reported to be significant for CTS⁹.

 

RESULTS

 

The study included fifty two patients, twelve (23%) were males while forty (77%) were females with age range 28-53 years (mean=41.5 years). The clinical presentations of the studied patients are shown in Table (1) and the results of different investigation modalities are shown in Table (2).

All patients underwent the standard open surgical technique for carpal tunnel release following the above investigations, the same surgical technique have been practiced by different surgeons. All surgeons were blinded to the results of investigations done, however not for patient’s symptoms or signs. They all reported positively presence of median nerve compression under the transverse carpal ligament with its relative thickening to different degrees during its intraoperative exposure.

All patients were followed up for a period not less than 12 weeks post-operatively. Thirty seven (71.1%) patients reported complete remission of previous symptomatology, while the rest fifteen (28.8%) patients showed marked amelioration of their complaint.

 

Table 1. The clinical presentations in all patients.

 

Clinical presentations	Number (%) (total=52)
Paresthesia or pain in at least 2 of the first 3 fingers	52 (100%)
Provocative clinical tests: -                   Phalen’s signs. -                   Tinel’s signs.	45 (86.5%) 43 (82.6%)
Objective motor deficit of thenar eminence muscles	None
Objective sensory dysfunction in the median nerve territory of the hand	None

 

Table 2. The results of different investigations (EDS, MRI and U/S).

 

Investigation tool and results	Number (%) (total=52)
Electro-diagnostic Studies (20 patients): (one or more of the following is diagnostic) 1. Prolonged motor and sensory latencies of the median nerve (Distal motor latency cutoff value: 4.2 msec). 2. Reduced sensory and motor conduction velocities. 3. Median-ulnar sensory latency difference.	17/20 (85%)
MRI examination (10 patients): (one or more of the following is diagnostic) 1. Swelling of the median nerve. 2. Increased signal intensity on T2W images. 3. Palmar bowing of the transverse carpal ligament.	10/10 (100%)
Ultrasosnographic examination (22 patients): (one or more of the following is diagnostic) 1. Enlargement of the median nerve at the proximal carpal tunnel with an increased cross-sectional area over 12 mm2. 2. Changes in median nerve echotexture consistent with edema (loss of fascicular discrimination with more or less homogeneous hypoechoic appearance). 3. Abrupt caliber change (notch sign) at the proximal margin of the flexor retinaculum. 4. Palmar bowing and thickening of the flexor retinaculum.	19/22 (86.3%)

 

 

DISCUSSION

 

Carpal tunnel syndrome is a common entrapment neuropathy of the median nerve characterized by pain and sensory disturbance along the distribution of the median nerve and thenar muscle atrophy in the advanced stages. The diagnosis may be made clinically and with electromyography (EMG). Ultrasound may also be valuable in the diagnosis of CTS. Several studies have demonstrated that carpal tunnel ultrasound in combination with clinical features and EMG was more sensitive and specific than clinical evaluation or EMG in isolation. Ultrasound has proved to be able to depict normal and pathologic nerves, including anatomical variants and abnormalities associated with CTS¹⁰.

The usual presenting feature of CTS is a pain syndrome known as brachialgia paresthetica nocturna. Patients, usually women in their fourth and fifth decade, are awakened from sleep in the early morning hours with pain radiating from the wrist proximally into the forearm and arm, and report numbness and tingling in the hand, stiffness of the fingers, and characteristic swelling sensations. All complaints rapidly resolve after repeated hand movements such as shaking. In the early stage no gross abnormalities can be observed within the nerve. Sensory disturbance usually appears before motoric deficiency since sensory fibers are more pressure sensitive than motoric fibers. According to Nora et al., 2005 paresthesia is the most characteristic feature followed by pain and cramps¹¹. In the current study, similar results was found where forty patients (77%) were females with mean age = 41.5 years. The most common presenting feature is paresthesia or pain in at least 2 of the first 3 fingers and it was found in all patients (100%).

Historically, clinical provocative tests such as Phalen’s and Tinel’s have been used to aid in the diagnosis of CTS. A wide range of sensitivities and specificities have been reported in the literature¹².  Phalen’s test is said to be positive when flexion at the wrist for 60 sec leads to pain or paresthesia in the distribution of the median nerve. These tests have quoted sensitivities of 10–90% and specificities of 33–100%. A detailed systematic review of over 3,000 cases reported a sensitivity of 68% and specificity of 73% for Phalen’s test and concluded that it was a useful test, but false negatives should be expected. Tinel’s test is said to be positive when tapping over the volar surface of the wrist causes paresthesia in the fingers innervated by the median nerve. Tinel’s is generally thought to be less sensitive than Phalen’s; however, specificities have been recorded as high as 100%¹³. In the present study the results of provocative clinical tests were: Phalen’s sign positive in (86.5%) of patients, while Tinel’s sign was positive in (82.6%).

Since American Academy of Neurology (ANN) previously stated the diagnosis of CTS is mostly clinical with the morphofunctional test aimed in confirming the diagnosis, No consensus exists regarding the type and number of nerve conduction tests needed to establish the neurophysiological diagnosis. Moreover, there is no consensus on the definition of abnormality. In addition to median nerve motor and wrist-digit sensory latency measurements, numerous new tests have been successively introduced to improve the sensitivity of nerve conduction tests. Performing multiple nerve conduction tests on an individual would increase the likelihood of obtaining a false positive result. Measurements of wrist-palm sensory conduction or median-ulnar comparison have been considered superior to distal motor and digit-wrist sensory latency measurements, particularly in detecting patients with mild CTS¹⁴.

The EDS diagnostic uncertainty associated with clinical signs may lead to clinicians non-selectively referring patients for nerve conduction studies with the belief that it represents a diagnostic gold standard. However, EDS have their own diagnostic hurdles. False negative and false positives can occur even when the most sensitive methods of EDS are used³. Graham¹⁵ looked at the value added by EDS in diagnosing patients with clinically defined CTS. They reported that for the majority of patients, EDS did not change the probability of diagnosing the condition. This was an interesting discovery and supports and emphasis on clinical history and examination in identifying patients with CTS.

Kamath and Stothard¹⁶ carried out a prospective study involving 107 patients to assess whether a similar structured health questionnaire would be able to diagnose CTS with similar sensitivities and specificities to EDS. They used symptom relief after surgery as the diagnostic gold standard and reported equivalent sensitivities and positive predictive values (PPV) between their questionnaire (sensitivity, 85%; PPV, 90%) and EDS (sensitivity, 92%; PPV, 92%). They concluded that such a questionnaire could be used to fast track those patients who scored highly for surgery, bypassing usual outpatient referrals and EDS. This goes against the recommendations of the American Academy of Orthopedic Surgeons, who recommend EDS for all patients being considered for surgery¹⁷. In the present study the electro diagnostic studies (EDS) performed for twenty patients with clinical criteria of CTS, only seventeen patients (85%) were positive and the remaining three patients were false negative.

A recent prospective study comparing the diagnostic utility of ultrasound versus EDS found equivalent sensitivities between the two techniques¹⁸. Sensitivities for EDS and ultrasound were 67.1% and 64.7%, respectively; however, if both EDS and ultrasound were considered together, the sensitivity increased to 76.5%. This suggests a role for ultrasound as a diagnostic adjunct to the established EDS. The study also highlights the diagnostic shortfalls of these investigations with 23.5% of patients with clinically diagnosed CTS remaining undetected (4).

On looking to the present study, 19 (86.3%) of 22 patients examined by ultrasonography were confirmed to be CTS according to the previous criteria. This result is comparable to the results yielded on electro diagnostic studies (EDS) performed in the same study (i.e. 85% were positive when tested for EDS) and this means equivalent sensitivities between the two techniques.

A prospective cohort study by Jarvik et al.¹⁹, attempted to further delineate the role of MRI in the diagnosis of CTS. They reviewed 105 patients and followed the patients for 1 year specifically looking at the ability of MRI to identify those patients likely to benefit from surgery and to compare its diagnostic usefulness to that of EDS. They demonstrated that both MRI and EDS were able to predict those patients who would benefit from surgical intervention; however, neither technique correlated well with patient’s perceived severity of symptoms. They did show some evidence to suggest that there is a patient preference for MRI over EDS with 76% of their patients reporting EDS to be unpleasant compared to 21% finding MRI unpleasant. Imaging provides anatomical information whilst EDS gives information on impairment of nerve fiber function and is able to rule out polyneuropathy and nerve conduction problems elsewhere in the body. With this in mind it is probable that the future of imaging will be in a supplementary role to the already established EDS in cases where anatomical clarification is required or where the results of EDS are equivocal⁴.

In the current series MRI was able to predict those patients who would benefit from surgical intervention; where all patients (100%) subjected to MRI examination were positive for CTS diagnostic criteria, confirming the clinical status. However, there is a patient preference for MRI over EDS, while others declare that the cost of MRI is unaffordable, hence EDS is the alternative. From our point of view neither EDS nor MRI would be better for the patient anyway; this is because of the high cost, technically demanding, and patient exposure to unpleasant complicated tools (invasive electrodes in EDS, noisy and time consuming in MRI).

It has been found that ultrasonography (especially the high frequency US) is highly valuable in assessing patients with clinical suspension of CTS, this may be related to many causes that include: wide availability, reasonable cost, time saving, well accepted to patients, no contraindications to its usage, and high accuracy rate. All these advantages make it superior to other contemporary investigation tools²⁰.

 

Conclusion

In conclusion, In mild cases of CTS, the sensitivity of the electrodiagnostic tests and US is very near, US is not an alternative diagnostic tool to electrodiagnostic tests and vice versa, but they are complementary; US provides anatomic information of the nerve and its surrounding structures while the electrodiagnostic tests provides information on the level of the lesion and the function of the nerve fibers. However, NCV and classic needle electromyography are indispensable to resolve clinical uncertainties and to rule out similar events such as cervical radiculopathy, brachial plexopathy and polyneuropathy. Finally, the diagnosis of CTS is essentially by clinical evaluation of the patient, however an added investigation is recommended to support the diagnosis. The dispute is what investigation tool that provides accurate and rapid diagnosis with the least cost. It was found that ultrasound is superior to other modalities in this respect.

 

[Disclosure: Authors report no conflict of interest]

 

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