Carpal Tunnel Syndrome Pain Treated With Low-Level Laser and Microamperes Transcutaneous Electric Nerve Stimulation: A Controlled Study

ABSTRACT. Naeser MA, Hahn K-AK, Lieberman BE, Branco KF. Carpal tunnel syndrome pain treated with low level laser and microamperes transcutaneous electric nerve stimulation: a controlled study. Arch Phys Med Rehabil 2002; 83:978-88. 

Objective: To investigate whether real or sham low-level laser therapy(LLLT) plus microamperes transcutaneous elec tric nerve stimulation (TENS) applied to acupuncture points significantlyreduces pain in carpal tunnel syndrome (CTS). 

Design: Randomized, double-blind, placebo-control, cross over trial. Patients and staff administered outcome measures blinded. 

Setting: Outpatient, university-affiliated Department of Vet erans Affairs medical center. 

Participants: Eleven mild to moderate CTS cases (nerve conduction study, clinical examination) who failed standard medical or surgical treatment for 3 to 30 months. 

Intervention: Patients received real and sham treatment series (each for 3– 4wk), in a randomized order. Real treat ments used red-beam laser (continuous wave, 15mW, 632.8nm) on shallow acupuncture points on the affected hand, infrared laser (pulsed, 9.4W, 904nm) on deeper points on upper extremityand cervical paraspinal areas, and microamps TENS on the affected wrist. Devices were painless, noninvasive, and produced no sensation whether theywere real or sham. The hand was treated behind a hanging black curtain without the patient knowing if devices were on (real) or off (sham). 

Main Outcome Measures: McGill Pain Questionnaire (MPQ) score, sensoryand motor latencies, and Phalen and Tinel signs. 

Results: Significant decreases in MPQ score, median nerve sensorylatency, and Phalen and Tinel signs after the real treatment series but not after the sham treatment series. Patients could perform their previous work (computer typist, handy man) and were stable for 1 to 3 years.

Conclusions: This new, conservative treatment was effec tive in treating CTS pain; larger studies are recommended. Key Words: Acupuncture; Carpal tunnel syndrome; Lasers; Pain; Rehabilitation; Transcutaneous electric nerve stimula tion. 

© 2002 by the American Congress of Rehabilitation Medi cine and the American Academy of Physical Medicine and Rehabilitation 

CARPAL TUNNEL SYNDROME (CTS) is an entrapment 

neuropathyof the median nerve at the wrist caused by compression of the median nerve as it passes from the forearm to the palm beneath the transverse carpal ligament.1 Signs and symptoms associated with CTS include paresthesias; numbness and tingling in the sensorydistribution of the median nerve for thumb, index, middle, and radial side of the ring finger; Tinel sign; Phalen sign; hypoesthesia; nocturnal awakening; specific pain diagrams of the hand; and sometimes hand weakness.2-4 Nerve conduction studies (NCSs) are the primarydefinitive test, although the exact millisecond latencies considered to be compatible with CTS varyacross studies.1,5-7 

The etiologyof CTS is unknown; however, it occurs more commonlyin workers with tasks involving repetitive hand movements (eg, computer keyboard typing, operating machin ery, assemblyline work). It maybe the result of a concentration of workload on a few smaller groups of muscles.3 In addition to ergonomic stressors, some systemic medical disorders (eg, diabetes mellitus, thyroid disease, rheumatoid arthritis, gout, obesity) and psychosocial factors may contribute to CTS. Be tween 1981 and 1991, the US Department of Labor, Bureau of Labor Statistics reported an almost 10-fold increase (from 23,000 to 223,600) in disorders “associated with re peated trauma.”8,9 In 1995, 50% of all workers with CTS missed  30 days of work.10 

Current standard treatments for work-related CTS include, initially, conservative treatments and, later, if necessary, sur gical release of the transverse carpal ligament. Conservative treatments include adjusting the work environment, and using wrist splints, and nonsteroidal anti-inflammatorydrugs.11 Di rect injection of steroids into the carpal tunnel mayprovide relief for only2 to 4 months,12 and at 18 months, only22% of patients maybe free of symptoms.13 

Surgical release of the transverse carpal ligament is per formed in approximately40% to 45% of CTS cases, with estimates of more than 460,000 procedures being performed each year, at a direct medical cost of more than $1.9 billion.7 After surgery, approximately one third of patients continue to experience pain and functional loss14; only40% regain normal function and 5% worsen.15,16 Office workers return to work in a few weeks and people who work in heavier labor require 4 to 6 months of rehabilitation. 

In 1993, the cost to treat 1 case of CTS without surgeryin California was $5246; with surgeryit was $20,925.17 The average cost to treat 1 case of CTS nationwide was about 

CARPAL TUNNEL SYNDROME: LOW-LEVEL LASER, Naeser 979 

$12,000.18 There is need for a new conservative treatment for CTS, which could be applied in the earlystages of the disorder to permit continued employment, to prevent disability, and to reduce the need for surgery. 

A new conservative treatment was tested in the present controlled study. The treatment uses low-level laser therapy (LLLT) and microamperes transcutaneous electrical nerve stim ulation (TENS) to stimulate acupuncture points. The term LLLT refers to the use of low-level lasers, which are class IIIb lasers (5–500mW, red-beam or near infrared; wavelength, 600 –1000nm). When applied to the skin, these lasers produce no sensation and do not burn the skin. Theyhave been ob served to increase cellular adenosine triphosphate (ATP) levels and to reduce pain in various studies (reviewed below). In addition, the application of microamps TENS has been ob served to increase cellular ATP levels and reduce pain (re viewed later). The application of LLLT (instead of acupuncture needles) to stimulate acupuncture points to treat pain has been reported in studies from China19 and other countries19,20 for more than 2 decades. 

Uncontrolled Studies Using Acupuncture or LLLT to Treat CTS Pain 

Two studies21,22 used acupuncture needles to stimulate acu puncture points to treat CTS pain, with success rates of 88% to 97%. The Chen21 studywith 36 cases included successful treatment of 14 CTS cases who had previouslyfailed to obtain satisfactorysymptom relief after surgical release. Follow-up after 5.1 years indicated continued pain relief in 24 of 29 cases.21 

Two other studies23,24 used LLLT to treat CTS pain with success rates of 77% to 91%. Weintraub24 treated 30 hands with a near infrared 830-nm, 30-mW laser (9J per point, 5 points, not acupuncture points, along the median nerve at the wrist/hand). Results showed a normalization of distal latencies for compound muscle action potential in 11 hands and a ten dencyto improve in 23%, reversing CTS in 77% of the cases. Wong et al23 treated a total of 35 CTS and repetitive stress injurycases with a near infrared 830-nm, 100-mW laser (12– 30J per point onlyat the posterior neck region, cervical 5 to thoracic 1, not at the affected wrist/hand area). In an 8-month period (10 treatments), 91.4% of the cases were successfully treated; no NCS data were provided. 

In a studycombining needle acupuncture, LLLT, and mi croamps TENS to treat CTS pain, Branco and Naeser25 found that 33 of 36 hands had more than a 50% reduction in pain after 12 to 15 treatments. The McGill Pain Questionnaire26 (MPQ) score was significantlyreduced posttreatment (P .0001). This included successful treatment of 14 hands after surgical release failed to provide satisfactorypain relief. The LLLT and mi croamps TENS treatment protocol used in the Branco and Naeser studywas the basic protocol originallydeveloped within this current controlled study, which function and 5% worsen.15,16 Office workers return to work in a few weeks and people who work in heavier labor require 4 to 6 months of rehabilitation.

Mechanisms of LLLT to Treat Pain 

Over the past 2 decades, LLLT has been used to treat pain associated with conditions such as musculoskeletal injuries, arthritic conditions, and postherpetic neuralgia.28-33 Some of the suggested mechanisms underlying therapeutic effects with LLLT have been reviewed34-36 and include the following: (1) increased ATP production bythe mitochondria37 and increased oxygen consumption on the cellular level,38 (2) increased se 

rotonin39 and increased endorphins (naloxone has been ob served to block the analgesic effect of LLLT with GaA1As laser),40 (3) anti-inflammatoryeffects,41,42 and (4) improved blood circulation to the skin in some cases (eg, postherpetic neuralgia,33 diabetes mellitus43). The primaryeffects of LLLT are considered to be photobiologic rather than photothermal.44 

Mechanisms of Microamps TENS to Treat Pain 

Microcurrent TENS is a relativelynew form of TENS that is used to treat chronic pain.45-47 Most standard TENS devices use milliamperes (mA) and the patient feels a tingling sensation from the surface electrodes. Milliamps TENS is believed to reduce pain, in part, as described bythe Gate Control Theory.48 Microamperes ( A) TENS is different in that the patient feels nothing; it is applied subthreshold. It has been observed to increase ATP concentrations and protein synthesis on the cel lular level, with the greatest stimulatoryeffects around 500 A.49 Currents greater than 5mA can decrease the ATP concentrations and the protein synthesis and transmembrane movement of metabolites.49 

Both LLLT and microamps TENS are appropriate for con trolled research in the treatment of pain because each device produces no sensation when applied to the skin. This study examined whether application of real or sham LLLT, plus microamps TENS to acupuncture points, significantlyreduces the signs and symptoms of mild to moderate CTS. This is the first controlled research to use real and sham LLLT plus microamps TENS to treat CTS pain. 

METHODS 

Participants 

Eleven CTS cases (11 hands from 9 men, 2 women) were included in the study(table 1). The patients ranged in age from 40 to 68 years (mean, 53.5y). All had failed to obtain satisfac torypain relief with conservative treatments, including nonste roidal anti-inflammatorydrugs and wrist splints, for a period of 3 to 30 months (mean, 16mo). One patient (case 4) had had surgical release of the transverse carpal ligament. At that time, 12 years before the present study, his CTS was associated with crutches; his more recent CTS was associated with his com puter work. These 11 patients were stratified into 2 groups 

(borderline/mild CTS, moderate CTS) based on a combination of electrodiagnostic and clinical findings. 

Electrodiagnostic testing. The NCSs were performed in the Rehabilitation Medicine Service, Department of Veterans Affairs (VA) Medical Center, Boston (KAKH), with surface stimulating and recording electrodes administered with stan dard methodologyusing a TD20 MK1 EMG/EP machine.a Before the NCSs were administered, hand skin temperature was measured with a Derma Therm® adhesive perfusion mon itor stripb placed on the dorsum of the hand for at least 15 seconds. The NCSs were performed onlyif the skin tempera ture was above 30°C. 

Treatment Equipment 

The research protocol used the following 3 treatment de vices. 

Device 1. A red-beam laserc (continuous wave, 15-mW, 632.8-nm, helium neon laser with a 2-mm diameter probe tip). The red-beam laser is presumed to have a shallow penetration into skin (eg, only0.8mm direct energy).50 The red-beam laser was applied to shallow acupuncture points located on the fingers and hand. 

Device 2. An infrared laserd (pulsed, 180ns “on” time, 9.4W, 904nm, gallium arsenide diode laser with a 5-mm di ameter probe tip). In addition to the single-diode probe, the infrared device had a second probe with a 4-diode arrayem bedded into a 6- by6-cm block. Each laser diode in the array had the laser properties identical to that of the single-diode probe. Because infrared laser has longer wavelengths than the red-beam laser, it is presumed to have a deeper tissue penetra 

CARPAL TUNNEL SYNDROME: LOW-LEVEL LASER, Naeser 981 

tion (up to an inch or more).50,51 The infrared laser was applied to deeper acupuncture points located at the elbow, shoulder, upper back, and cervical paraspinal areas. 

Device 3. A microamps TENS devicee (580 A–3.5mA), which was applied to the affected wrist. 

The lasers were calibrated before use, and the laser and TENS probes were wiped with alcohol before each treatment. 

Procedures 

Study design. This was a randomized, double-blind, pla cebo-control, crossover trial. The staff administering the treat ments were different from the staff administering the outcome measures; the latter were blinded to which series of treatments (real or sham) each patient was about to receive or had just received. The staff administering the treatments were not blinded. Patients were randomized to receive either a series of real treatments first or a series of sham treatments first. Patients were tested on the outcome measures within a month before entering the study(entrybaseline) and within a week after the end of each treatment series (posttest 1, posttest 2). The posttest 1 scores also served as pretreatment scores for the second treatment series. 

Treatment procedure. Each patient received 2 series of 9 to 12 treatments, real or sham. Each series lasted 3 to 4 weeks, and patients were treated 3 times a week (Monday, Wednesday, Friday). Each session required 35 to 45 minutes. After the first treatment series, patients were reevaluated (posttest 1) and then crossed over to the alternative treatment series followed by posttest 2. Seven patients received the sham treatment series first and 4 received the real treatment series first. 

During sham laser treatments, there was no emission from either the red or infrared lasers, even though the laser probe was held on the same acupuncture points/areas for the same amount of time. Dynatronics Corporation installed a laser beam cutoff mode on the red-beam laser, which was used during the sham treatments to block emission of the laser beam. Also, the Dynatron 1620c had a programmable timer that emitted a sound after a fixed period. Thus, the patient heard the same sound after 66.6 seconds (1J), whether the treatment was real or sham. 

The emission from the single-probe infrared laser was blocked during sham treatment bysetting the laser output mode to that for the 4-diode array. Likewise, when the 4-diode array was used during sham treatment, the output mode was set to that for the single probe. The Respond Systems infrared laser emitted a short tone after 30 seconds of laser beam emission The microamps TENS device was turned off during sham treatment. 

During each treatment, the patient was seated comfortablyin a chair at an adjustable table. To guarantee that the patient remained blinded as to which treatment condition was being administered, all treatments were performed on the affected upper extremity, with the patient’s elbow, forearm, and hand placed underneath and through the bottom of a hanging black curtain. This prevented the patient from seeing whether the red-beam laser was on or off. The infrared laser is beyond the visible spectrum. 

The treatments were administered bylicensed acupunctur ists. The anatomic locations of the acupuncture points listed are described in acupuncture textbooks.52 There were 3 sequential steps to each treatment session. 

Step 1. The red-beam laser was placed perpendicularly directlyon the skin at the center of the distal wrist crease of the affected hand, acupuncture point PC 7 (pericardium meridian), the point closest to the median nerve at the wrist crease (7J, 225J/cm2, 7.7min). 

Step 2. The circular electrode (4-cm diameter) for the microamps TENS device was applied to the skin and centered over acupuncture point PC 7, located at the center of the wrist crease, and the grounding pad was applied to the skin and centered over acupuncture point TW 4 (triple warmer), located on the dorsum of the wrist. After these were taped into place, the device was turned on. As the power intensitywas gradually increased, the patient was asked if he/she felt anystimulation or tingling at either electrode site. Immediatelyafter the patient reported sensation, the intensitylevel was decreased to a sub threshold level at which the patient reported no sensation. When the MicroStim 100 TENS device is used properly, there is no sensation. During real treatment, after the subthreshold intensityhad been established and set, a pulsed frequencyof 292Hz was used for 2 minutes followed bya pulsed frequency of 0.3Hz for 18 minutes (as suggested bythe manufacturer). The microamps TENS treatment required 20 minutes. 

During sham treatment, the same procedure was followed; however, the TENS device was turned off immediatelyafter the patient felt the initial stimulation or tingling sensation. The adjustment from 292 to 0.3Hz required moving a switch that produced an audible click. This same switch was adjusted after 2 minutes during the sham condition (even though the device had been turned off). Thus, the patient heard the same click during each treatment condition. 

Step 3. While the TENS device was taped into place at the wrist for 20 minutes, the red-beam laser was applied to additional acupuncture points on the affected hand (1J, 32.3J/cm2, 66.6s per point). This included 6 points on the fingers and 5 to 8 points on the hand and wrist. The points on the fingers included Lu 11 (lung), LI 1 (large intestine), PC 9, TW 1, Hrt 9 (heart), and SI 1 (small intestine). These points were chosen because theymark the origin and termination (Well points) for 6 acupuncture meridians that pass through the wrist. LI 1, for example, is indicated to treat numbness in the index finger, a common complaint in CTS.52 Other points chosen for treatment on the wrist and hand (eg, Lu 9, Hrt 7, Hrt 8, PC 8, Ba-Xie points in the web-spaces between the fingers) were chosen because theyare local points for treatment of hand pain. 

Also during step 3, the infrared laser was applied to a minimum of 5 deeper acupuncture points on the upper extrem ity, the upper trapezius, and cervical paraspinal areas. Each acupuncture point was treated for a minimum of 1 minute, at each of 3 pulse settings (eg, 3500, 584, and 73 pulses per second [pps]), with energydensities ranging from 1.81J/cm2 at the highest frequencyto .04J/cm2 at the lowest frequency.

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