Comparison of Diagnostic Modalities for Carpal Tunnel Syndrome: A Systematic Review

Carpal tunnel syndrome (CTS) is a common nerve entrapment disorder that affects millions, particularly older adults and women. It causes numbness, tingling, and discomfort in the hand, primarily affecting the median nerve. Risk factors include occupation (e.g., jobs involving repetitive motion or vibrating tools) and conditions such as obesity, pregnancy, and diabetes. Accurate diagnosis is critical for effective treatment, with nerve conduction studies (NCS) and ultrasound (US) being two key diagnostic methods. Each approach has strengths, limitations, and diagnostic utility, necessitating a comparison to determine the best use case for each tool. This comprehensive systematic review aims to compare the diagnostic accuracy and clinical utility of NCS and US in diagnosing CTS and provide conclusions on the most appropriate modality in different clinical scenarios.  A PubMed literature review conducted in August 2024 identified 49 studies. Of these, 31 were excluded for design and non-English language, evaluating only a single modality, or lacking comparison of diagnostic utility. The remaining 18 studies, published between 2008 and 2023, directly comparing NCS and US for diagnosing CTS were included. We included studies published within 20 years that directly compared measures of diagnostic accuracy, disease severity, and identification of anatomic abnormalities between US and NCS. Novel approaches, such as the inching technique, and newer measurements, such as transverse carpal ligament thickness, were also considered. Descriptive statistics were calculated, and Welch's t-test was used to compare means, with p-values indicating statistical significance.  A total of 18 studies met the inclusion criteria for analysis and included cohort (n=9), case-control (n=7), cross-sectional (n=1), and case-series (n=1) designs. NCS demonstrated high diagnostic accuracy, with an average sensitivity of 83% and improved sensitivity up to 96.7% using the inching technique. The comparison showed a higher average sensitivity for US than NCS (84.9% vs. 83.3%, respectively). Similarly, US had a higher average specificity than NCS (71.2% vs. 66.6%, respectively). The differences between the sensitivity and specificity of US and NCS were not statistically significant (p=0.76 and p=0.72, respectively). Studies comparing NCS and US showed that each method offers distinct advantages based on clinical severity, with US being more sensitive for structural assessment and NCS offering better functional insights.  Both NCS and US have unique diagnostic roles in CTS. While NCS remains the gold standard for evaluating nerve function, US offers a viable, less invasive alternative, particularly for detecting early structural changes. Patient-specific factors, clinical presentation, and disease severity should guide the choice between the two. This study, however, is limited by its design, the small number of eligible high-quality studies, and conflicting evidence among them. While the review employed robust methodology, its narrow focus restricted the pool of available research. Variability in study populations, methodologies, and outcome measures further contributed to inconsistent findings, underscoring the need for high-quality, standardized studies. Further research is needed to refine diagnostic protocols, especially when using both techniques to enhance diagnostic accuracy and patient outcomes.