Ultrasound in the Management of Carpal Tunnel Syndrome
Carpal tunnel syndrome (CTS) is the most common entrapment neuropathy, affecting 9% of women, and it is responsible for significant morbidity and occupational absence. Clinical assessment is used for initial diagnosis and nerve conduction (NC) studies are currently the principal test used to confirm the diagnosis. Sensitivity of NC studies is >85% and specificity is >95%. There is now good evidence that US can be used as an alternative to NC studies to diagnose CTS. US can assess the anatomy of the median nerve and also identify pathology of the surrounding structures that may compress the nerve. Median nerve enlargement (cross-sectional area ≥10 mm at the level of the pisiform bone or tunnel inlet) is the most commonly used parameter to diagnose CTS on US, and sensitivity has been reported to be as high as 97.9% using this parameter. US may also be used to guide therapeutic corticosteroid injection into the carpal tunnel—thus avoiding median nerve injury—and to objectively monitor the response to treatment. There is now sufficient evidence to propose a new paradigm for the diagnosis of CTS that incorporates US. US is proposed as the initial diagnostic test in CTS based on similar sensitivity and specificity to NC studies but higher patient acceptability, lower cost and additional capability to assess carpal tunnel anatomy and guide injection.
Carpal tunnel syndrome (CTS) is the most common entrapment neuropathy. The prevalence in the general population is estimated at 9% for woman and 0.6% for men. Most cases of CTS are idiopathic; however, it can occur as a result of trauma, particularly fracture or dislocation of the carpal bones, as well as secondary to RA, hypothyroidism, acromegaly, the oral contraceptive pill, diabetes mellitus and during pregnancy.
The median nerve in the carpal tunnel lies between the flexor retinaculum (FR) superiorly and the flexor tendons (flexor digitorum profundus, flexor digitorum superficialis and flexor pollicus longus) and carpal bones (scaphoid and trapezium) inferiorly. The nerve is prone to compression at this site. The exact cause of compression in not known, but a number of factors have been implicated. The tendons generate considerable upward force during finger movement as they move towards the FR, thus generating a compression force between the tendons and the FR. There is evidence that the median nerve moves from side to side during these movements to avoid direct contact with the tendons. When fibrosis of the subsynovial connective tissue occurs in CTS, these movements are likely to be restricted, leading to worsening compression. Histology of synovial specimens does not support a major role for inflammation, as only 10% showed evidence of inflammatory change. However, specimens do show evidence of chronic degeneration, supporting the theory of decreased mobility of the tissues. The compression within the canal is thought to disturb blood flow and lead to venous congestion and oedema. Prolonged epineural oedema causes fibroblast invasion into the affected tissue and scar tissue formation around the median nerve. The effect on circulation is believed to have a direct impact on the nerve with demyelination and axonal loss.
Assessment of risk factors emphasizes the important role for genetic predisposition, with heritability estimated at 46% in twin studies. Increased BMI is a significant independent risk factor for CTS in those <63 years of age, but it is less important in older patients. The risk of developing severe CTS as documented by nerve conduction (NC) studies also increases with obesity. There is evidence that occupational factors play a role, with occupations with more hand-intensive activities having a higher incidence. This review explores new and conventional approaches to accurate diagnosis, particularly highlighting the role of US. Current conservative and surgical treatment options are also reviewed.
Abstract and Introduction
Abstract
Carpal tunnel syndrome (CTS) is the most common entrapment neuropathy, affecting 9% of women, and it is responsible for significant morbidity and occupational absence. Clinical assessment is used for initial diagnosis and nerve conduction (NC) studies are currently the principal test used to confirm the diagnosis. Sensitivity of NC studies is >85% and specificity is >95%. There is now good evidence that US can be used as an alternative to NC studies to diagnose CTS. US can assess the anatomy of the median nerve and also identify pathology of the surrounding structures that may compress the nerve. Median nerve enlargement (cross-sectional area ≥10 mm at the level of the pisiform bone or tunnel inlet) is the most commonly used parameter to diagnose CTS on US, and sensitivity has been reported to be as high as 97.9% using this parameter. US may also be used to guide therapeutic corticosteroid injection into the carpal tunnel—thus avoiding median nerve injury—and to objectively monitor the response to treatment. There is now sufficient evidence to propose a new paradigm for the diagnosis of CTS that incorporates US. US is proposed as the initial diagnostic test in CTS based on similar sensitivity and specificity to NC studies but higher patient acceptability, lower cost and additional capability to assess carpal tunnel anatomy and guide injection.
Introduction
Carpal tunnel syndrome (CTS) is the most common entrapment neuropathy. The prevalence in the general population is estimated at 9% for woman and 0.6% for men. Most cases of CTS are idiopathic; however, it can occur as a result of trauma, particularly fracture or dislocation of the carpal bones, as well as secondary to RA, hypothyroidism, acromegaly, the oral contraceptive pill, diabetes mellitus and during pregnancy.
The median nerve in the carpal tunnel lies between the flexor retinaculum (FR) superiorly and the flexor tendons (flexor digitorum profundus, flexor digitorum superficialis and flexor pollicus longus) and carpal bones (scaphoid and trapezium) inferiorly. The nerve is prone to compression at this site. The exact cause of compression in not known, but a number of factors have been implicated. The tendons generate considerable upward force during finger movement as they move towards the FR, thus generating a compression force between the tendons and the FR. There is evidence that the median nerve moves from side to side during these movements to avoid direct contact with the tendons. When fibrosis of the subsynovial connective tissue occurs in CTS, these movements are likely to be restricted, leading to worsening compression. Histology of synovial specimens does not support a major role for inflammation, as only 10% showed evidence of inflammatory change. However, specimens do show evidence of chronic degeneration, supporting the theory of decreased mobility of the tissues. The compression within the canal is thought to disturb blood flow and lead to venous congestion and oedema. Prolonged epineural oedema causes fibroblast invasion into the affected tissue and scar tissue formation around the median nerve. The effect on circulation is believed to have a direct impact on the nerve with demyelination and axonal loss.
Assessment of risk factors emphasizes the important role for genetic predisposition, with heritability estimated at 46% in twin studies. Increased BMI is a significant independent risk factor for CTS in those <63 years of age, but it is less important in older patients. The risk of developing severe CTS as documented by nerve conduction (NC) studies also increases with obesity. There is evidence that occupational factors play a role, with occupations with more hand-intensive activities having a higher incidence. This review explores new and conventional approaches to accurate diagnosis, particularly highlighting the role of US. Current conservative and surgical treatment options are also reviewed.
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