"This study aims to investigate ultrasonographic parameters of the median nerve in healthy individuals and patients with mild and moderate carpal tunnel syndrome (CTS).

Specifically, investigator will assess the cross-sectional area (CSA) at the proximal carpal tunnel and the wrist/forearm ratio (WFR), and determine their diagnostic thresholds.

İnvestigators will also evaluate correlations between these ultrasound measures and clinical and electrophysiological findings, including pain, symptom severity, functional status, and quality of life (Visual Analog Scale, Boston Carpal Tunnel Questionnaire, SF-36).

A) STUDY RATİONALE:

The median nerve runs along the medial aspect of the arm, passes anterior to the elbow, continues between the two heads of the pronator teres muscle in the forearm, progresses toward the wrist, and traverses the carpal tunnel before entering the hand

The carpal tunnel is an anatomical structure formed by the carpal bones, comprising the proximal row (scaphoid, lunate, triquetrum, pisiform) and the distal row (trapezium, trapezoid, capitate, hamate). The roof of the tunnel is known as the flexor retinaculum, attaching laterally to the scaphoid and trapezium bones and medially to the hamate and pisiform bones.

The primary structures passing through the carpal tunnel include the four flexor digitorum superficialis tendons, four flexor digitorum profundus tendons, the flexor pollicis longus tendon, and the median nerve. The median nerve innervates the volar surface of the first three digits and the radial half of the fourth digit, including the nail beds of these fingers.

Median neuropathy is the most common peripheral neuropathy, and the most frequent site of entrapment is the carpal tunnel at the wrist. Mechanical compression of the nerve leads to local ischemia and demyelination of nerve fibers, resulting in paresthesia, pain, and motor dysfunction. Paresthesia is initially more pronounced at night and may later occur during the day. In advanced cases, motor functions may also be affected.

Carpal tunnel syndrome (CTS) is more prevalent in women, although the male-to-female ratio varies across studies. Recent studies suggest that women are three times more likely to develop CTS compared to men. CTS is most commonly observed in individuals aged 50-54 years. Its etiology and pathophysiology are multifactorial, including idiopathic causes (most common), anatomical variations, genetic predisposition, trauma, obesity, space-occupying lesions in the wrist, connective tissue disorders, hypermobility, metabolic and endocrine diseases, pregnancy, lactation, and menopause.

Despite its prevalence and well-characterized clinical presentation, the optimal diagnostic strategy for CTS remains uncertain. Clinical history and physical examination remain indispensable for diagnosis, although their diagnostic accuracy is variable. CTS diagnosis primarily relies on clinical history and examination. There is no standardized definition, but clinicians generally use a combination of specific symptoms indicative of the syndrome.

Although clinical diagnostic criteria vary, common symptoms in CTS patients include nocturnal paresthesia that awakens the patient, symptom relief by shaking or squeezing the hands, pain or paresthesia triggered by gripping or forceful hand use, and sensory symptoms affecting the first, second, third digits, or the relevant portion of the fourth digit.

The sensitivity and specificity of diagnostic tests for CTS vary in the literature. Commonly used diagnostic maneuvers include Tinel's sign, Phalen test, reverse Phalen test, carpal tunnel compression test, and the flick sign. Current evidence suggests that electrodiagnostic evaluation represents the gold standard for CTS diagnosis. The most frequently employed method in electrodiagnostic assessment is nerve conduction study (NCS), which provides quantitative data and enhances diagnostic certainty beyond clinical observation. Electrodiagnostic testing serves as an objective marker for confirming mononeuropathy.

Typically, CTS diagnosis is based on history and physical examination, with NCS serving as a complementary tool to confirm clinical findings. The American Association of Neuromuscular & Electrodiagnostic Medicine (AANEM) still recommends electrodiagnostic evaluation as the gold standard in clinically suspected CTS. Electrodiagnostic evaluation demonstrates high sensitivity (>85%) and specificity (~95%) for CTS confirmation, making it reliable and reproducible. Although NCS directly measures nerve function changes, it can be uncomfortable for patients and may show limited correlation with clinical severity. When NCS is not tolerated or is non-informative, ultrasonography (US) can identify pathology and easily localize structures.

Unlike functional studies, US provides valuable anatomical information about tissues. It is portable, allows assessment of intraneural blood flow, and enables detailed evaluation of the entire median nerve course. US permits direct visualization of the nerve, allowing assessment of its position within the carpal tunnel and relationships with surrounding structures. CTS represents the most common entrapment neuropathy in which US has recently emerged as a valuable diagnostic tool. Recent studies indicate that US may have sensitivity and specificity comparable to, or even exceeding, electrodiagnostic studies, with excellent intra- and inter-observer reliability.

Evidence-based guidelines suggest that ultrasonographic measurement of the median nerve cross-sectional area (CSA) at the wrist is appropriate and can be presented as a diagnostic test for CTS. Multiple studies report high sensitivity and specificity of US for CTS diagnosis.

Typical US findings in CTS include nerve flattening at the site of entrapment with proximal swelling (Notch sign). Additional features may include hypoechogenicity due to increased intraneural fluid, loss of fascicular pattern, and increased vascularity within the tunnel indicating inflammation. Various US parameters have been evaluated for diagnostic value, including hypervascularity, median nerve notch, median-ulnar nerve ratio, and flattening ratio, though most recent studies focus on CSA accuracy.

Measurement of median nerve CSA at the proximal carpal tunnel (at the level of the scaphoid-pisiform bones) is widely used in CTS sonographic diagnosis and is the easiest parameter to visualize. Several meta-analyses indicate that proximal CSA demonstrates the highest diagnostic reliability among ultrasonographic parameters. CSA ratios, such as wrist-to-forearm ratio (WFR), inlet-to-outlet ratio (IOR), and nerve flattening ratio, help control for patient variability. Highest sensitivity and specificity have been reported for WFR, measured approximately 12 cm proximal to the distal wrist crease.

Expert consensus recommends including WFR in median nerve US, particularly for patients with very small or large nerves, and CSA measurement should be included. Panel members also noted that CSA may be misleading in patients over 70 years. Some studies comparing electrodiagnostic evaluation and US report similar sensitivity and specificity for both techniques.

In clinical practice, the choice between US and electrodiagnostic evaluation depends on the specific scenario, aiming to achieve maximal diagnostic accuracy. Clinicians may prefer US over electrodiagnostics to confirm diagnosis in patients intolerant to NCS or in resource-limited settings with portable, battery-operated US devices. A significant correlation has also been reported between median nerve size at the carpal tunnel and electrodiagnostic severity, although methodological differences contribute to variable threshold values across studies.

Taken together, current literature and guidelines highlight the increasing role of US in CTS diagnosis. In this study, investigators aim to assess the diagnostic utility of US measurements of median nerve CSA at the proximal carpal tunnel (scaphoid-pisiform level) and WFR (proximal forearm to distal wrist) in healthy individuals and patients with mild to moderate CTS.

In the United States, CTS results in an annual cost of approximately $2 billion and associated productivity losses. Lifetime prevalence among workers is estimated at 7%, with about 5 million workers affected, of whom ~70% have work-related CTS. Previous CTS-related worker compensation costs have reached billions of dollars, prompting the publication of the Work-Related Carpal Tunnel Syndrome Diagnosis and Treatment Guideline. Given its impact on quality of life and functionality, investigator plan to investigate correlations between US parameters and pain, symptom severity, quality of life, and functionality in eligible participants.

B) STUDY OBJECTİVES:

The aim of this study is to investigate the diagnostic threshold values of ultrasonographic parameters in healthy individuals and in patients with mild to moderate carpal tunnel syndrome (CTS) confirmed by clinical and electrophysiological evaluation. Specifically, the study will assess: (1) the cross-sectional area (CSA) of the median nerve at the proximal entry of the carpal tunnel (scaphoid-pisiform level), and (2) the wrist-to-forearm ratio (WFR), defined as the ratio of the median nerve CSA at the proximal carpal tunnel to the CSA at approximately 12 cm proximal in the forearm.

Additionally, the study aims to evaluate the correlation between these ultrasonographic parameters and clinical and electrophysiological findings, as well as patient-reported outcomes, including pain, symptom severity, hand function, and quality of life, as measured by the Visual Analog Scale (VAS), Boston Carpal Tunnel Questionnaire (BCTQ), and Short Form-36 (SF-36).

C) ANTİCİPATED OUTCOMES:

It is expected that individuals with mild to moderate carpal tunnel syndrome (CTS), as confirmed by clinical and electrophysiological evaluation, will demonstrate increased ultrasonographic parameters compared to healthy controls. Specifically, an increase in the cross-sectional area (CSA) of the median nerve at the proximal entry of the carpal tunnel (scaphoid-pisiform level) and in the wrist-to-forearm ratio (WFR), defined as the ratio of CSA at the proximal carpal tunnel to CSA approximately 12 cm proximal in the forearm, is anticipated.

CSA and WFR values are expected to correlate with disease severity. Based on these findings, ultrasonography may serve as a potential alternative to electrophysiological evaluation for the diagnosis and staging of CTS. Determining diagnostic threshold values aligned with clinical staging may allow for CTS classification based on combined ultrasonographic and clinical findings.

Compared to electrophysiological studies, ultrasonography offers several advantages, including direct visualization of anatomical structures, shorter examination time, improved patient comfort, and reduced resource utilization, making it a more practical and cost-effective diagnostic approach.

Furthermore, increasing disease severity is expected to be associated with higher pain and symptom scores, and decreased hand function and quality of life. Consequently, CSA and WFR measurements are anticipated to provide valuable biomarkers not only for CTS diagnosis but also for assessing the clinical impact of the disease.

D) SUBJECT SAFETY AND RELİABİLİTY:

No significant issues are anticipated regarding participant safety or reliability during the study assessment process.

E ) STUDY PROTOCOL:

This analytical cross-sectional study is planned to include participants aged 18-60 years who present to the Physical Medicine and Rehabilitation outpatient clinics of Istanbul University, Istanbul Faculty of Medicine, Esnaf Hospital between July 17, 2025, and December 30, 2025. Eligible participants will consist of healthy individuals and patients diagnosed with mild or moderate carpal tunnel syndrome (CTS) based on clinical findings and electrophysiological evaluation, who do not meet any exclusion criteria.

Prior to participation, all subjects will receive written and verbal information regarding the study objectives, procedures, and duration, and written informed consent will be obtained using the "Informed Consent Form." Following the assessments, participants will complete questionnaires evaluating pain, symptom severity, functionality, and quality of life. Pain intensity will be assessed using the Visual Analog Scale (VAS), symptom severity and functional status with the Boston Carpal Tunnel Questionnaire (BCTQ), and health-related quality of life with the Short Form-36 (SF-36).

The BCTQ consists of two subscales: the first section includes 11 items assessing symptom severity on a 1-5 point scale (1 = minimal symptoms, 5 = maximal symptoms), and the second section includes 8 items assessing functional capacity, also scored 1-5 (higher scores indicate lower function). Mean scores are calculated separately for symptom severity and functional capacity. The VAS measures pain intensity on a 0-10 scale (0 = no pain, 10 = worst possible pain). The SF-36 consists of 36 items covering eight dimensions of health, scored from 0 (worst) to 100 (best), and is validated for use in general populations. All questionnaires will be self-administered by participants.

Clinical evaluation, electrophysiological measurements, and the VAS, BCTQ, SF-36, and ultrasonography (USG) assessments will be conducted independently by two separate evaluators. After confirming eligibility, the first evaluator will record clinical and electrophysiological findings and administer the questionnaires. Participants will be assigned sequential numbers by the first evaluator. The second evaluator (thesis supervisor), blinded to the clinical and electrophysiological results, will perform all USG measurements according to participant numbers and record cross-sectional area (CSA) and wrist-to-forearm ratio (WFR) data. All data will be kept independent and confidential to ensure assessor blinding and objectivity.

All assessments (electrophysiological measurements, questionnaires, and USG) will be performed on the same day.

Ultrasonography Procedures:

USG will be performed using a Canon Aplio 500 system (Canon Medical Systems, Japan) with a high-frequency linear probe (7-18 MHz). Participants will be seated with the forearm supinated, elbows flexed at 90°, wrists in neutral position, and hand muscles relaxed. Hands will rest on a cushion on the thighs for stabilization. The median nerve will be scanned from the elbow to the wrist for anatomical variations. At the proximal carpal tunnel (scaphoid-pisiform level), CSA measurements will be obtained manually at least three times. Additionally, the median nerve CSA at approximately 12 cm proximal to the distal wrist crease will be measured, and the wrist-to-forearm ratio (WFR) calculated.

Electrophysiological Procedures:

Electrophysiological evaluations will be performed using a four-channel Nihon-Kohden electromyography system (MEM-4200K, Neuropack 8, Tokyo, Japan) following the guidelines of the American Association of Neuromuscular and Electrodiagnostic Medicine (AANEM).

The evaluator performing electrophysiology will be blinded to USG results.

Median nerve distal motor latency (DML) and conduction velocity will be recorded from the abductor pollicis brevis (APB) with orthodromic stimulation (G1-stimulator: 7 cm, G1-G2: 4 cm).

Median nerve sensory distal latency (DSL) and conduction velocity will be recorded antidromically from the second digit (G1-stimulator: 13 cm, G1-G2: 4 cm).

Median-ulnar sensory peak latency comparison will be performed from the fourth digit (antidromic, G1-stimulator: 13 cm, G1-G2: 4 cm).

Ulnar nerve sensory DSL and conduction velocity will be recorded from the fifth digit (G1-stimulator: 11 cm, G1-G2: 4 cm).

Ulnar nerve distal motor latency and conduction velocity will be recorded from the abductor digiti minimi (ADM) with orthodromic stimulation from the wrist and 3 cm distal to the medial epicondyle (G1-stimulator: 7 cm, G1-G2: 4 cm).

All measurements will be performed in a room maintained at 25°C, ensuring hand temperature above 32°C.

F ) STATİSTİCAL METHODS

Descriptive statistics will be presented as mean ± standard deviation, median, minimum, and maximum values for continuous variables, and as frequency (n) and percentage (%) for categorical variables. Normality of continuous variables will be assessed using the Kolmogorov-Smirnov and Shapiro-Wilk tests.

For comparisons among three independent groups:

Parametric continuous variables will be analyzed using one-way ANOVA.

Non-parametric continuous variables will be analyzed using the Kruskal-Wallis test.

Categorical variables will be compared using the Chi-square test.

Correlation analyses will be conducted as follows:

Spearman correlation for non-parametric continuous variables.

Pearson correlation for parametric continuous variables.

Sample size calculation was performed using G*Power software (ANOVA: Fixed effects, omnibus, one-way). For three groups, assuming a medium effect size (0.4), α = 0.05, and 80% power, the minimum required total sample size was calculated as 68 participants. Considering potential dropouts due to exclusion criteria, 75 participants (150 hands) are planned to be included in the study.

Sensitivity and specificity will be assessed using Receiver Operating Characteristic (ROC) curve analysis. A p-value < 0.05 will be considered statistically significant, with 95% confidence intervals reported where appropriate. Statistical analyses will be performed using IBM SPSS Statistics version 22.0 (Chicago, IL, USA).

G) PLANNED TESTS WITH DURATION and LABORATORY INFORMATION:

Electrophysiological Examination (Nerve Conduction Studies) Approx. 20 minutes duration Examiner: Prof. Dr. Sina Arman (Esmailzadeh) Department of Physical Medicine and Rehabilitation, Istanbul University, Istanbul Faculty of Medicine, Esnaf Hospital Outpatient Clinics, Suleymaniye Takvimhane Cad., No:19, Fatih, Istanbul, Turkey Phone Number: +90 536 648 1111 Email adress: sinabox@gmail.com

Ultrasonographic Evaluation Approx. 15 minutes Examiner: Dr. Cem Can Yücel Department of Physical Medicine and Rehabilitation, Istanbul University, Istanbul Faculty of Medicine, Esnaf Hospital Outpatient Clinics, Suleymaniye Takvimhane Cad., No:19, Fatih, Istanbul, Turkey Phone number: +90 506 645 1834 Email adress: yucelccan19@icloud.com

Notes:

Electrophysiological evaluation will include median and ulnar nerve conduction studies according to standard protocols.

Ultrasonographic assessment will focus on the cross-sectional area (CSA) of the median nerve at the proximal carpal tunnel and wrist-to-forearm ratio (WFR).

All questionnaires will be self-administered by participants, and validated Turkish versions will be used.

This study will be conducted as a single-center study at the Department of Physical Medicine and Rehabilitation, Istanbul University, Istanbul Faculty of Medicine, Esnaf Hospital Outpatient Clinics, Istanbul, Turkey.

INCLUSION CRITERIA:

Participants aged 18-60 years who meet the eligibility criteria as either healthy controls or patients with carpal tunnel syndrome (CTS) are eligible for the study.

1. Healthy Participants:

   • Absence of any clinical symptoms related to CTS.
   • Normal evaluation according to electrophysiological criteria for CTS.

2. Participants with CTS:

Participants must have a diagnosis of mild or moderate CTS based on clinical findings and electrophysiological evaluation.

b.1) Clinical Findings/Symptoms: b.1.1) Symptoms:

(A)- Sensory symptoms in the 1st, 2nd, 3rd finger, or lateral half of the 4th finger, or in any combination of these.

(B)- Symptom relief with hand-shaking or squeezing movements.

(C)- Pain or paresthesia triggered by hand grip or forceful hand use.

(D)- Nocturnal paresthesia causing the patient to wake from sleep.

b.1.2) Diagnostic Tests/Signs:

• Tinel's sign
• Phalen test
• Reverse Phalen test
• Carpal tunnel compression test
• Flick sign

Clinical CTS Diagnosis:

Symptoms must be present for at least three months and at least the presence of sensory symptoms (A) plus at least one of B, C, or D, together with at least one positive diagnostic test/sign, is required for clinical diagnosis.

b.2) Electrophysiological Evaluation:

• Mild CTS: Median-ulnar sensory peak latency difference ≥ 0.4 ms in the 4th finger, and median sensory distal latency of the 2nd finger ≥ 2.8 ms, with conduction velocity < 50 m/s. Sensory nerve action potential (SNAP) ≥ 12 μV.
• Moderate CTS: Median distal motor latency of the 2nd finger between 4 ms and 5.5 ms, with conduction velocity < 50 m/s. Compound muscle action potential (CMAP) ≥ 5 mV.

E) EXCLUSİON CRİTERİA:

1. For Participants Meeting Patient Criteria:

   • Participants diagnosed with mild or moderate CTS who meet any of the following criteria will be excluded:
   • History of physical therapy for carpal tunnel syndrome within the last 6 months.
   • History of injection into the carpal tunnel.
   • History of carpal tunnel release surgery.
   • Presence of thenar atrophy in the hand.
   • History of cardiac pacemaker implantation.
   • History of lymphedema in the studied extremity.
   • History of cervical radiculopathy.
   • Presence of tenosynovitis in the ipsilateral upper extremity.
   • Presence of another compressive neuropathy in the ipsilateral upper extremity.
   • History of peripheral polyneuropathy or comorbidities that may cause peripheral polyneuropathy (e.g., diabetes mellitus).
   • Presence of metabolic disease.
   • History of fracture in the hand, wrist, or forearm.
   • Active pregnancy.
   • Presence of open wounds on the wrist.
   • History of uncontrolled systemic disease (endocrinologic, cardiovascular, pulmonary, hematologic, hepatic, renal, active systemic inflammatory disease, and/or malignancy).
   • History of inflammatory rheumatic or autoimmune disease.
   • Distal motor latency of the median nerve > 5.5 ms on electrophysiological evaluation.
   • Age < 18 or > 60 years.
   • Cognitive or mental incapacity preventing understanding or completion of questionnaires.
   • Anatomical variations affecting ultrasonographic assessment of the median nerve (e.g., bifid median nerve, persistent median artery).
   • Anatomical variations affecting electrophysiological measurements (e.g., Martin-Gruber anastomosis).

2. For Healthy İndividual Participants:

Participants will be excluded if they meet any of the following criteria:

• Age < 18 or > 60 years.
• Cognitive or mental incapacity preventing understanding or completion of questionnaires.
• Presence of any clinical symptoms potentially related to CTS based on established clinical criteria.
• Electrophysiological findings consistent with CTS, based on defined diagnostic thresholds.

This cross-sectional analytical study is designed to include participants based on a power analysis and results from previous studies. To achieve 80% statistical power at a 95% confidence level, at least 68 participants are required; however, considering that a few participants may be excluded due to not meeting eligibility criteria, a total of 75 participants (150 hands) will be enrolled. The study will target individuals aged 18-60 years who present to the Physical Medicine and Rehabilitation outpatient clinic at İstanbul University, İstanbul Faculty of Medicine, Esnaf Hospital. Participants will include healthy individuals as well as patients diagnosed with mild to moderate carpal tunnel syndrome (CTS) based on clinical findings and electrophysiological evaluation. Before enrollment, all participants will be fully informed about the study, and written informed consent will be obtained. Demographic characteristics, including age, height, weight, will be recorded for all participants.