The study included 60 subjects, 57 females and 3 males. They were divided into two groups: a patient group and a control group. The patient group included 29 females and 1 male patient. Their ages ranged from 25 to 53 years, with a mean age of 35.4 ± 7.8 years. Patients included in the study were clinically suspected to have carpal tunnel syndrome, and their sensory nerve conduction studies showed early starting or mild degrees of entrapment according to the classification of Bland (2000) (The mild degree of entrapment corresponds to delayed median nerve sensory peak latency and normal motor studies, while in early starting entrapment there is normal sensorimotor median nerve conduction studies and positive comparative studies). We used the median-ulnar ring finger antidromic comparative sensory studies (American Association of Electrodiagnostic Medicine et al. 2002). We excluded patients with other neuromuscular disorders, proven clinically or electrodiagnostically, e.g., cervical radiculopathy and polyneuropathy. We also excluded patients with systemic diseases which may be associated with neuropathy, e.g., diabetes mellitus, and patients in whom EMG examination is contraindicated, e.g., bleeding disorders. We also recruited 30 age- and sex-matched healthy volunteers to serve as a control group; their ages ranged from 22 to 43 years with mean age of 32.7 ± 5.9 years.
Clinical assessment
Full history taking and thorough clinical examination were undertaken with highlights on decreased overall sensation, response to pinprick and light touch over the palmar surface of the lateral three and half fingers, and thenar weakness. Tinel sign, Phalen test, and median nerve compression test were performed.
Electrodiagnosis
Electrophysiologic studies were carried out using a Nihon Kohden® MEB_9200K Neuropack machine (Tokyo, Japan), software V.08.11 (Tokyo, Japan), in the Clinical Neurophysiology unit of Kasr Alainy Hospital, Cairo University. Motor and sensory nerve conduction studies (NCS) to the median and ulnar nerves and median-ulnar ring finger antidromic sensory studies were performed according to standard techniques (Preston and Shapiro 2013). The normal cut off values were as follows: Median motor NCS: distal latency ≤ 4.4 ms, amplitude ≥ 4.0 mV, and conduction velocity ≥ 49 m/s. Ulnar motor NCS: distal latency ≤ 3.3 ms, amplitude ≥ 6.0 mV, and conduction velocity ≥ 49 m/s. Median sensory NCS,: peak latency ≤ 3.5 ms, amplitude ≥ 20 μV, conduction velocity ≥ 50 m/s. Ulnar sensory NCS: peak latency ≤ 3.1 ms, amplitude ≥ 17 μV conduction velocity ≥ 50 m/s. Median-ulnar ring finger antidromic sensory study was considered normal up to 0.4 ms peak latency difference (Preston and Shapiro 2013).
EMG examination and SFEMG were carried out using a disposable small concentric needle with a recording area of 0.031 mm2 (Technomed®, Netherland). The muscles examined for patients and controls were the abductor pollicis brevis (APB), abductor digiti minimi (ADM), and extensor digitorum communis (EDC) muscles. For conventional EMG, the pattern of insertional activity, the presence or absence of resting activity, the motor unit potentials morphology at moderate contraction, the pattern of recruitment, and the interference pattern at maximum effort were assessed. For SFEMG, the high- and low-frequency filters were 10 and 2 kHz, respectively (Ertas et al. 2000). The needle was inserted in the muscle and the subject was instructed to perform weak contraction of the examined muscle. The needle was manipulated carefully until a stable signal of at least two upward peaks was shown on the monitor. Then, the needle was kept in position until 50–100 sweeps of the fiber pair were recorded. The position of the needle was then changed and the procedure was repeated 10 times to collect 10 fiber pairs for each subject with a total of 300 fiber pairs for each group. For each fiber pair, the mean consecutive difference (MCD) was calculated as well as the mean MCD of all trials and if there was abnormal blocking. When the mean consecutive difference/mean sorted difference (MCD/MSD) value exceeded 1.25, which means the inter-potential interval was influenced by the variations in the firing rate, we used the MSD instead of the MCD to represent the neuromuscular jitter, because the MSD is a mathematical algorithm that reduces the effect of this factor (Sanders and Stålberg 1996).
Statistical methods
Patients’ data were tabulated and processed using software Microsoft Excel 2010. Quantitative variables were expressed by mean ± standard deviation (SD). Independent samples t-test was used to assess the significance of differences between two subject groups, and p value ≤ 0.05 was considered statistically significant.