Effect of Different Wrist Positions on Median Nerve Conduction in Patients with and without Carpal Tunnel Syndrome - A Comparative Study.

Sir,

Carpal Tunnel syndrome is most common compressive neuropathy of upper limb affecting Median Nerve with 3.8% prevalence rate.[1] The pathology of the condition suggest that median nerve may be affected due to individual or multiple factors in carpal tunnel area like elevated pressure, mechanical injury, ischemic damage etc.[2] Subjective assessment of the condition include combination of the history, physical examination and result of provocative tests. Provocative tests are easy to perform and a combination of positive results increases the likelihood of CTS.[3] Nerve conduction study (NCS) is gold standard method for diagnosis of CTS. It is used to identify underlying pathology such as extent of demyelination and axonal loss etc.[4]

This quasi experimental study consisted of 30 subjects and 2 groups i.e., experimental group subjects with CTS (n = 15) and control group subjects without CTS (n = 15). The study was done with Institutional ethical clearance and with participant's informed consent. The inclusion criteria for experimental group was, patients clinically diagnosed with unilateral CTS. The exclusion criteria were patients with other condition affecting Nerve conduction i.e., Ulnar neuropathy, pregnant women and patients clinically diagnosed with CTS having negative NCS findings. The eligibility criteria for control subjects was age matched healthy individual without CTS.

The demographic details were collected after the participants were included in the study. Participants in the experimental group were required to provide the answers for questionnaire for Symptom Severity and Functional Status. After collecting the details, NCS test was performed. The limb temperature was assured at 32-33 degree Celsius for conduction testing.[5] Standards of nerve NCS were maintained as per the norms and was kept uniform for all the participants. In addition to it median NCS was performed in Phalen's test and Reverse Phalen's test position. Diagnosis of the Carpal Tunnel Syndrome was confirmed based on confirmatory guideline of nerve conduction parameter.[6]

Demographic characteristics of both the groups at baseline are presented in Table 1. We have found statistically significant difference between both the groups in motor distal and proximal latency, sensory latency and Sensory Nerve Action Potential (SNAP) with standard position of testing [Table 2]. Motor distal, proximal latency and sensory latency was more prolonged by 2.12, 2.05 msec and 0.44 msec, respectively in experimental group as compared to control group. There is statistically significant difference in distal motor and sensory latency with different wrist positions in the experimental and control group [Table 3]. There was high positive correlation between Symptom severity and motor distal latency while negligible correlation between Symptom severity and other NCS findings. There was negligible correlation between Functional severity and NCS findings [Table 4].

Table 1

Baseline characteristics

Characteristics		Control Group (N = 15) (Mean ± SD)	Experimental Group (N = 15) (Mean ± SD)
Gender (N)	Male	5	6
	Female	10	9
Dominant Side (N)	Right	12	12
	Left	3	3
Tested Side (N)	Right	12	8
	Left	3	7
Age (Years)		36.75 ± 10.89	43.73 ± 10.27
BMI (kg/m2)		22.54 ± 1.90	22.73 ± 1.99

Descriptive statistics for age and BMI. Frequency analysis for gender and dominant side of participants in both the groups

Table 2

Between group comparison of median nerve conduction study parameters

Parameters	Control Group (Mean ± SD)	Experimental Group (Mean ± SD)	P Value
Median Motor
DL	3.33 ± 0.28	5.45 ± 1.24	0.00
PL	7.43 ± 0.47	9.48 ± 1.19	0.00
Distal CMAP	14.38 ± 3.76	11.46 ± 4.35	0.08
MNCV	56.04 ± 4.11	59.26 ± 13.36	0.653
Median Sensory
DL	2.54 ± 0.21	2.98 ± 0.59	0.01
SNAP	35.24 ± 10.94	23.86 ± 11.88	0.013

DL = Distal Latency (ms), PL = Proximal Latency (ms), CMAP = Distal Compound Muscle Action Potential (mV), MNCV = Motor Nerve Conduction Velocity (m/s), SNAP = Sensory Nerve Action Potential (µV).Mann Whitney U – test, Significance level < 0.05

Table 3

Between group comparison of Median Nerve Conduction Study parameters with different wrist position

Parameter		Control Group (Mean ± SD)	Experimental Group (Mean ± SD)	P Value
Median Motor
DL	Neutral	3.33 ± 0.28	5.45 ± 1.24	0.00
	Phalen’s	3.50 ± 0.36	6.28 ± 0.99	0.00
	Reverse P.	3.32 ± 0.39	5.79 ± 1.13	0.00
PL	Neutral	7.43 ± 0.47	9.48 ± 1.19	0.00
	Phalen’s	7.55 ± 0.55	10.81 ± 1.34	0.00
	Reverse P.	7.46 ± 0.53	10.06 ± 1.10	0.00
Distal CMAP	Neutral	14.38 ± 3.76	11.46 ± 4.35	0.081
	Phalen’s	15.70 ± 4.73	12.68 ± 3.71	0.125
	Reverse P.	14.70 ± 3.68	13.29 ± 3.98	0.407
MNCV	Neutral	56.04 ± 4.11	59.26 ± 13.36	0.63
	Phalen’s	56.86 ± 3.54	52 ± 5.08	0.01
	Reverse P.	55.89 ± 4.11	53.99 ± 5.64	0.23
Median Sensory
s	Neutral	2.54 ± 0.21	2.98 ± 0.59	0.011
DL	Phalen’s	2.71 ± 0.21	4.08 ± 0.76	0.00
	Reverse P.	2.56 ± 0.23	3.33 ± 0.7	0.00
	Neutral	35.24 ± 10.94	23.86 ± 11.88	0.014
SNAP	Phalen’s	33.45 ± 11.46	28.33 ± 6.75	0.125
	Reverse P.	36.70 ± 10.13	28.48 ± 9.26	0.017

Friedman’s test applied for the comparison of Median NCS parameters with different wrist position between both the group. Significance level <0.05

Table 4

Correlation between Symptom severity and Functional Status with median nerve Conduction Study parameters with Carpal Tunnel Syndrome

Variables	Correlation Coefficient (r)	P Value
SS - Motor Distal Latency	0.897	0.00
SS - CMAP	-0.059	0.834
SS - MNCV	-0.04	0.990
SS - Sensory Latency	0.018	0.949
SS - SNAP	0.266	0.338
FS - Motor Distal Latency	-0.094	0.738
FS - CMAP	-0.147	0.601
FS - MNCV	-0.17	0.544
FS - Sensory Latency	- 0.223	0.424
FS - SNAP	- 0.091	0.748

SS = Symptom Severity, FS = Functional Severity. Spearman’s Correlation for Symptom severity and Functional Status with median nerve Conduction Study parameters with Carpal Tunnel Syndrome. Significant Level < 0.05

Our study findings were suggestive that there was no statistical difference in Motor Conduction Velocity between the groups but the findings in the experimental group suggest that some participants were having slowed conduction velocity. The reason for slowed conduction velocity may be some of the participants with CTS having axonal loss. All the sensory NCS parameters such as sensory latency and SNAP were found to be affected because sensory symptoms are more likely to developing in early stages of the CTS as compared to motor symptoms.[7] NCS parameters with Phalen's and reverse phalen's test findings shows latency prolongation with Phalen's test as compared to neutral which shows reversal with reverse phalen's test in both the groups. Reasons for the similar findings in both groups may be changes in the pressure in carpal tunnel with wrist flexion and extension as suggested by evidence.[8] Study also shows significant difference in motor and sensory latency between two groups. Which indicates the output of provocative tests differs significantly between patients with and without carpal tunnel syndrome. Latency is more commonly affected parameter showing better differentiation with change in position as it may be affected by change in compartmental pressure. Literature also suggest that a change in pressure in the carpal tunnel may be also one of the factors which may be affecting the electro physiologic findings.[8]

High positive correlation has been reported between Symptom severity and distal motor latency. The reason may be as patient experiences discomfort, thumb weakness, difficulty in holding objects, it is likely to affect the distal motor latency in patients with CTS. There was negligible correlation between functional status and NCS parameters because functional status domain includes certain activities like buttoning clothes, carrying grocery buckets which could be done by unaffected hand also.[9]

On the basis of the result obtained, it can be concluded that change in the wrist position is one of the factors which affects NCS parameters such as median distal motor and sensory latency, SNAP. Phalen's test posture affects NCS parameters more as compared to Reverse Phalen's posture. Furthermore, there is high correlation between Symptom severity and median motor distal latency and negligible correlation between functional status and NCS parameters. Further study can be done on large sample for more accurate results with assured steps for reduction in measurement error.

Financial support and sponsorship

Nil.

Conflicts of interest

There are no conflicts of interest.