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Diagnostic considerations in carpal tunnel syndrome

Kasius, K.M.

2015

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Kasius, K. M. (2015). Diagnostic considerations in carpal tunnel syndrome.

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Abstract

Objective – Warming cold limbs by hot water immersion prior to nerve

conduction studies may be cumbersome in certain patients. The aim of the present study is to test whether application of hot packs would be as efficient as hot water immersion.

Methods – Cold limbs of 10 healthy volunteers were warmed: in half of

subjects by hot packs and, after cooling down, by hot water immersion; vice versa in the other half. Motor and sensory nerve conduction studies of upper and lower extremities were performed before and after warming with two different methods.

Results – There are no relevant differences in temperatures or nerve conduction

velocities after warming with either hot packs or water.

Conclusion – Hot packs are as effective as hot water immersion for warming

2

Introduction

Abnormally low nerve conduction velocity (NCV) is an important electrodiagnostic sign of peripheral nerve dysfunction. Therefore, the measurement of nerve conduction velocities is an important electrodiagnostic test in peripheral neuropathies. It is well known that temperature has several influences on different variables of nerve conduction studies.1-3 _{Therefore, and according to}

generally accepted guidelines, nerve conduction studies must be performed with skin temperatures of at least 31° Celsius.1,4 _{Often, warming of the limbs}

will be necessary. A commonly used and proven effective method is warming cold limbs by using hot water immersion (at temperatures of around 37°-42° Celsius) for 15-30 minutes.3,5 _{However, in routine clinical practice, this may be}

a rather cumbersome procedure for examinations in the Intensive Care Unit, in bedridden patients, and in the elderly or severely disabled patients. Alternative methods are electrical heating methods, external heaters such as blow dryers, infrared heaters, heating lamps, hot water immersion blankets, and hot packs.6,7

The efficacy of different warming methods has not been intensively investigated with an objective basis. The present study investigated the efficacy of hot packs, applied over the skin of the limbs, in order to test whether this method would be as efficient in warming the limbs as the more commonly used hot water immersion method.

Methods

The efficacy of two warming methods, i.e. hot packs vs. hot water immersion, was estimated in 10 healthy individuals by means of a crossover design.

The healthy volunteers, mean age 36.8 y (range 21-64), were recruited from hospital personnel. All gave written informed consent, and the local medical ethics committee approved the study. No subject had signs or symptoms of peripheral nerve disease, such as polyneuropathy or mononeuropathies of the relevant nerves, as determined by a brief questionnaire and neurological examination. Skin temperature of each stimulation and recording site was measured with a fast-reading (less than one second) infrared thermometer (62 Mini IR thermometers, Fluke Biomedical, Cleveland OH, USA). The procedure was performed initially with low skin temperature (baseline session A). In four persons the skin temperature was lowered by immersion in cold water.

Next, in half of the patients, the limbs were warmed by careful application of hot packs (Thermocomfort®_{) on the skin of proximal as well as distal upper}

34

Chapter 2 | Warming cold limbs in nerve conduction studies

16 x 25 cm or 20 x 42 cm plastic bags filled with an exothermic fluid (Figure 1). These can be activated by squeezing a small metal device inside the bag, which starts a reversible exothermic reaction. Subsequently, the bag immediately radiates heat of 40-50º Celsius for at least 1 hour. After each use, the bags are immersed in boiling water (modified dish washer). After cooling down towards room temperature, the packs can be stored for future use. Several hot packs were applicated side by side on the skin accurately such that all skin above the studied nerve trajectory was warmed. The skin was carefully protected against direct contact with the surface of the hot pack with a towel between the hot pack and the skin. It takes about 1-2 minutes per limb to cover the limb completely and carefully with towels and hot packs.

Finally, after cooling down in the air for at least 30 minutes, the limbs were warmed again in temperature controlled running hot water of 37º Celsius for 30 minutes (session C). Limbs were dried thoroughly.

In the other patients, limbs were first warmed in temperature-controlled water for 30 minutes (session C) and, after cooling down to baseline following examination, warmed by hot packs (session B).

After each warming session, limbs were covered with blankets prior to examination to keep the subject warm. Nerve conduction studies were performed as quickly as possible after warming in order to prevent undesirable cooling down. It has been suggested by others that little skin cooling occurs within 6 minutes after hot water immersion.5 _{The subjects were investigated in a}

temperature controlled room with a mean ambient temperature of 20° Celsius. In order to demonstrate that the degree of increase of NCV does not

2

differ significantly following both warming methods on cold limbs, this study investigated the effect on nerve conduction parameters of hot packs vs. hot water immersion. All patients underwent standardized motor and sensory nerve conduction studies (NCS) of ulnar, median, fibular and sural nerves, in accordance with the American Association of Neuromuscular and Electrodiagnostic Medicine (AANEM) guidelines.8 _{NCS were performed using a Viking Myograph type IV}

(Nicolet Biomedial Inc., Madison, WI, USA). Electrophysiological studies were all performed by the same examiner (JR). All stimulation and recording sites were marked with non-washable ink, to ensure that identical sites were used for the different warming methods.

For motor nerve conduction studies: compound signals peak-to-peak amplitudes were measured as well as onset latencies. Compound muscle action potentials (CMAPs) were recorded using surface electrodes in the tendon-belly montage. For sensory nerve conduction studies: onset latency, conduction velocity, and peak-to-peak amplitude were determined.

Upper limb:

• Median nerve distal motor latency and motor and sensory NCV forearm: the median nerve was stimulated at the wrist and at the cubital fossa. Sensory nerve action potentials (SNAP) were recorded from dig II, using ring electrodes.

• Ulnar nerve distal motor latency (DML) and motor and sensory NCV forearm: the ulnar nerve was stimulated at the wrist, below and above the elbow. SNAPs were recorded from dig V using ring electrodes.

Lower limb:

• Fibular nerve DML and motor NCV lower leg: the fibular nerve was stimulated at the dorsum of the ankle, distal to the fibula head, and at the popliteal fossa, respectively. CMAPs were recorded from the extensor digitorum brevis muscle.

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Chapter 2 | Warming cold limbs in nerve conduction studies

Statistical analysis

Data concerning nerve conduction studies and temperatures were processed using Microsoft Office Excel 2010 and all statistical analyses were performed using IBM SPSS Statistics 20.

Wilcoxon signed rank test was used for pairwise comparison of NCV values, distal motor latencies, and temperatures before and after warming with the described methods, and principally, between the different methods of warming the limbs. P < 0.05 was considered to be statistically significant.

Results

Temperature

The boxplots in Figure 2A show the spread and mean temperatures at recording sites for the different warming methods. For all recording sites, mean temperatures were significantly higher after warming with hot packs compared with hot water immersion. In Figure 2B the grand average of temperature of all measurements is plotted in boxplots.

Mean temperature did not significantly differ according to the two heating protocols. Hot packs: 34.3 ± 1.00 vs. 34.3 ± 0.4 for order A – B – C vs. A – C – B, respectively. Hot water: 32.7 ± 0.24 vs. 32.3 ± 0.39 for order A – B – C vs. A – C – B, respectively.

All tested persons preferred the use of hot packs to hot water immersion of the limbs, because of comfort and convenience. No adverse events occurred.

Electrophysiology

Data regarding NCV, DML values, and amplitudes are plotted in Figure 3 and presented in detail in Table 1. As expected as compared to baseline, NCV increased and DML decreased substantially after warming of the limbs with either method.

In all cases, the average increase of NCV and decrease of DML values was statistically significant different after both warming methods compared to the initial low temperature.

2

Figure 2.

A. Boxplots: temperatures at recording sites according to different warming techniques. Lines represent values for individual subjects.

B. Mean temperatures, of all measurements, according to different warming techniques. Lines represent values for individual subjects.

A

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Chapter 2 | Warming cold limbs in nerve conduction studies

Table 1.

Nerve conduction parameters and temperatures according to different warming methods

Cold (A)

Hot packs (B)

Hot water (C)

P

Median nerve motor NCS

Forearm NCV (m/s) 53.4 ± 3.75 61.1 ± 4.89 59.7 ± 4.90 A vs. B: 0.005; A vs. C: 0.005; B vs. C: n.s. Temperature (°C) 27.6 ± 1.27 34.7 ± 1.11 33.0 ± 0.42 A vs. B: 0.005; A vs. C: 0.005; B vs. C: 0.008 DML (ms) 3.62 ± 0.65 2.52 ± 0.44 2.63 ± 0.40 A vs. B: 0.005; A vs. C: 0.005; B vs. C: n.s. Amplitude (mV) 19.5 ± 6.81 15.5 ± 5.21 16.3 ± 6.48 A vs. B: 0.005; A vs. C: 0.013;B vs. C: n.s. Temperature (°C) 25.1 ± 1.69 34.0 ± 1.16 32.1 ± 0.50 A vs. B: 0.005; A vs. C: 0.005; B vs. C: 0.008

Median nerve sensory NCS

Distal NCV (m/s) 44.6 ± 7.35 62.9 ± 3.84 60.8 ± 5.70 A vs. B: 0.005; A vs. C: 0.005; B vs. C: n.s. Amplitude (μV) 45.4 ± 28.9 37.9 ± 17.2 43.4 ± 21.0 A vs. B: n.s.; A vs. C: n.s.;B vs. C: 0.047 Temperature (°C) 25.2 ± 2.68 33.6 ± 0.89 33.6 ± 0.89 A vs. B: 0.005; A vs. C: 0.005;B vs. C: 0.009 Forearm NCV (m/s) 56.4 ± 5.87 65.2 ± 4.61 65.6 ± 4.55 A vs. B: 0.005; A vs. C: 0.005; B vs. C: n.s. Amplitude (μV) 28.7 ± 14.9 16.6 ± 8.59 21.0 ± 9.99 A vs. B: 0.007; A vs. C: 0.017; B vs. C: 0.017 Temperature (°C) 26.5 ± 1.60 34.7 ± 1.14 33.4 ± 0.63 A vs. B: 0.005; A vs. C: 0.005; B vs. C: 0.008

Ulnar nerve motor NCS

2

Ulnar nerve sensory NCS

Distal NCV (m/s) 43.1 ± 7.84 62.7 ± 6.08 59.2 ± 4.44 A vs. B: 0.005; A vs. C: 0.005; B vs. C: n.s. Amplitude (μV) 52.9 ± 23.4 45.4 ± 17.5 50.6 ± 28.4 A vs. B: n.s; A vs. C: n.s; B vs. C: n.s. Temperature (°C) 23.7 ± 2.18 33.7 ± 0.88 31.3 ± 0.68 A vs. B: 0.005; A vs. C: 0.005; B vs. C: 0.005 Forearm NCV (m/s) 58.9 ± 4.79 69.4 ± 2.87 66.8 ± 3.30 A vs. B: 0.007; A vs. C: 0.007; B vs. C: n.s. Amplitude (μV) 30.5 ± 16.7 19.5 ± 9.49 25.7 ± 17.1 A vs. B: 0.017; A vs. C: 0.009; B vs. C: n.s. Temperature (°C) 26.5 ± 1.30 34.7 ± 1.48 32.8 ± 0.74 A vs. B: 0.005; A vs. C 0.005; B vs. C: 0.005

Fibular nerve motor NCS

Motor NCV (m/s) 43.8 ± 3.63 49.4 ± 4.74 47.3 ± 4.09 A vs. B: 0.005; A vs. C: 0.005; B vs. C: 0.008 Temperature (°C) 25.8 ± 1.64 34.8 ± 1.18 33.0 ± 0.76 A vs. B: 0.005; A vs. C: 0.005; B vs. C: 0.007 DML (ms) 5.19 ± 0.87 3.55 ± 0.36 3.64 ± 0.44 A vs. B: 0.005; A vs. C: 0.007; B vs. C: n.s. Amplitude (mV) 10.3 ± 4.40 8.73 ± 2.46 9.20 ± 2.80 A vs. B: n.s.; A vs. C: n.s.; B vs. C: n.s. Temperature (°C) 25.3 ± 1.86 34.3 ± 1.19 32.9 ± 0.90 A vs. B: 0.005; A vs. C: 0.005; B vs. C: 0.022

Sural nerve sensory NCS

40

2

Figure 3. Boxplots: DML, sensory and motor nerve conduction velocities, and amplitudes of median, ulnar, fibular, and sural nerve, according to different warming techniques.

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Chapter 2 | Warming cold limbs in nerve conduction studies

respectively). The DML of the ulnar nerve was significantly lower after warming with hot packs compared with hot water immersion (1.9 ± 0.24 ms vs. 2.1 ± 0.25 ms, respectively).

In most cases, amplitudes were smaller after warming. Neither median nor ulnar SNAP after distal stimulation was significantly different after warming with both methods. There was no statistically difference in CMAP amplitude recorded from the extensor digitorum brevis muscle after warming with either method.

Discussion

In daily practice, the use of hot packs has been proven to work well for several reasons. In the present study, the effectiveness of this method was compared to the effectiveness of hot water immersion. Temperatures reached significantly higher values after warming with hot packs compared with hot water immersion. Moreover, all subjects reported a preference for warming with hot packs. Almost all velocities and latencies were within normal limits after warming. Therefore, we conclude that hot packs are at least as effective as hot water immersion for the sake of warming cold limbs prior to electrodiagnostic testing.

The main advantage of the method with hot packs is that they are easily applicable. There are other advantages, which may be of use as a procedure in ambulant subjects. In spite of rigorously warming the limbs with hot water immersion, the skin temperature may still drop gradually, shortly after withdrawing of the warm water especially in patients with autonomic dysfunction. Nerve conduction remains unchanged for about 6 min after removal of the external warmer.5 _{In the present study however, all hot packs were removed after}

warming. The reached temperature, the increase in NCV, and decrease of DML may therefore all be an underestimation. In daily practice, it is possible to keep the hot packs in place until the specific limb is tested, thus minimizing further temperature drop after the warming procedure because the surface temperature of 40 to 50° Celsius lasts for at least 1 hour. In this way, limbs can be kept on temperature for any time in contrast with hot water immersion. If temperature drops nevertheless during extensive nerve conduction studies, it is easy to reheat cooled limbs with hot packs.

There is discussion about the desirable length of warming prior to the electrophysiological examination. Some suggest 20 to 40 minutes, depending on the initial temperature.7 _{Rutkove et al.}3 _{suggested that 30 minutes is}

2

minutes is desirable;5 _{therefore we chose a fixed 30-minute warming time in all}

patients and for both warming methods in order to accurately compare warming methods. Since in this study, achieved temperatures were higher after warming with hot packs compared to hot water, one can speculate that acceptable skin temperatures are achieved after a shorter warming period, for instance, 15 to 20 minutes. This would be a more acceptable time in daily practice. We did not, however, study the minimal necessary warming time using hot packs in the present study. This could be the subject of future investigation.

Shorter warming periods may result in suboptimal near-nerve temperatures.6

In the present study, only skin temperature was recorded, which is considered to be a reliable index for intramuscular and subcutaneous temperature change.9

Since nerve conduction parameters were essentially the same in both sessions, we do not have indications that near-nerve temperature differed after warming with both methods.

Another important issue is hygiene. After hot water immersion the bath has to be cleaned thoroughly, which takes time, while hot packs are always clean after preparation in boiling water for 20 minutes. In addition, disabled and elderly patients may have difficulty in immersing their limbs in the bath with danger of falling, which obviously is avoided when using application of hot packs.

The main drawback of the use of hot packs is the risk of burns. In the past, a few cases of local burns have been described generally as a result of direct contact between the hot packs and the skin.10,11 _{Therefore, it is extremely}

important to apply a towel between the hot packs and the skin, in order to prevent direct contact. The rate of transfer of heat to the skin depends on the thermal penetration coefficients of the skin and the surface of the hot object, which is very slow with material such as towels.10 _{Moreover, it is important to take precautions}

in certain patients, for example sedated patients (in the Intensive Care Unit), patients with cognitive impairment, and patients with polyneuropathy.

A weakness of this study is the relatively small number of subjects. However, the differences are large and results were confirmed in nerve conduction studies of both upper and lower extremities. Many different nerves were tested and showed all the same results (not presented). Nevertheless, it is not possible to draw definite conclusions, and the results should be verified in a larger study. Another possible weakness is that only healthy subjects were examined, and we did not compare both warming methods in patients with, for example, polyneuropathy. It is known that in diseased nerves, temperature dependence of nerve conduction variables differs from healthy nerves.3,12,13 _{Since reached}

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Chapter 2 | Warming cold limbs in nerve conduction studies

without relevant differences in nerve conduction parameters, we believe the final results of nerve conduction studies in patients would be essentially the same. This may be, however, a subject for further research.

Conclusion

2

References

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3. Rutkove SB. Effects of temperature on neuromuscular electrophysiology. Muscle Nerve 2001; 24: 867–882.

4. Halar EM, DeLisa JA, Soine TL. Nerve conduction studies in upper extremities: skin temperature corrections. Arch Phys Med Rehabil 1983; 64: 412–416.

5. Franssen H, Wieneke GH. Nerve conduction and temperature: necessary warming time. Muscle Nerve 1994; 17: 336–344.

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BE, eds. Electromyography and Neuromuscular Disorders 3rd Edition. Elsevier Health Sciences; 2012.

8. Jablecki CK, Andary MT, Floeter MK, et al. Practice parameter: Electrodiagnostic studies in carpal tunnel syndrome: Report of the American Association of Electrodi-agnostic Medicine, American Academy of Neurology, and the American Academy of Physical Medicine and Rehabilitation. Neurology 2002; 58: 1589–1592.

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10. Feldman KW, Morray JP, Schaller RT. Thermal injury caused by hot pack application in hypothermic children. Am J Emerg Med 1985; 3: 38–41.

11. Khan MAA, Jamnadas-Khoda B, Gorman M, Ghosh SJ. Physiotherapy-induced hot pack burn in a paraplegic Paralympic athlete. J Burn Care Res 2011; 32: e167.

12. Franssen H, Notermans NC, Wieneke GH. The influence of temperature on nerve conduction in patients with chronic axonal polyneuropathy. Clin Neurophysiol 1999; 110: 933–940.