Carpal tunnel syndrome : how does it develop and what puts people at risk? Some of the answers might surprise you!
Carpal tunnel syndrome (CTS) is the most common neuro-compressive disease in the world (1) and may bring to mind images of office workers pounding on keyboards day-in and day-out. But we've also had patients whose condition result from having a low functioning thyroid! As well as people with varying occupations which put them at risk, such as electricians and plumbers. And did you know gender can be a risk factor for carpal tunnel syndrome? One study in China found women could be four times more likely to get the condition!(1)
What is Carpal Tunnel Syndrome?
CTS may be defined as a unilateral or bilateral paresthesia, which is a disturbed sensation of pain, tingle or numbness, in the first three digits and the lateral half of the fourth digit of the hand. It results from compression of the median nerve, which innervates those specific regions of the hand. The compression of the median nerve is prone to happen, with repetitive over-use and/or other risk factors, within the 'carpal tunnel', a narrow passage enclosed by the transverse carpal ligament on one side. It is this transverse carpal ligament which gets severed in surgical procedures to alleviate CTS.
The pain of CTS may be felt in one or more areas including the wrist, palm, or forearm in the vicinity of compression. This may be a result of 'axonal retrograde degeneration', which is a form of damage to the median nerve.(2) When this happens, loss of strength may occur, and opposition of the thumb and atrophy of the opponens pollicis muscle may develop, as well as loss of fine motor skills.
Mild CTS often presents with intermittent symptoms while severe CTS may result in permanent loss of sensation and even paralysis of the thumb.
Anatomy of the 'Carpal Tunnel'
The 'carpal tunnel' is formed by the seven carpal bones posteriorly and the transverse carpal ligament (also called the 'anterior annular ligament' or 'flexor retinaculum') anteriorly. The transverse carpal ligament is attached to several bones in the wrist including the pisiform, hamate, scaphoid and the trapezium. Through this tunnel pass the tendons of the long flexor muscles of the fingers with their protective synovial fluid-filled tendon sheath (ulnar bursa), the flexor pollicis longus tendon, and the tendon of the flexor carpi radialis with its own synovial tendon sheath (radial bursa), or 'tenosynovium'. Superficial to all these tendons lies the median nerve, which is just below the transverse carpal ligament. This ligament acts to prevent malfunctions and ruptures of the flexor tendons. With contraction of the flexors of the wrist and fingers, especially with the wrist in flexion, the tendons in the carpal tunnel move in such a way that the median nerve is trapped between the tenosynovium and the transverse carpal ligament, placing compressive force against it.
CTS can have varying underlying contributing causes and these may have to be addressed quite differently. However, a largely unifying consideration is that any condition that increases the volume of the structures within the carpal tunnel or causes a narrowing of the tunnel itself can result in impingement on the median nerve.
Conditions that may lead to narrowing in the tunnel are often trauma and injury-based, but not always. These may include deformity from subluxation of the carpals, separated distal radius and ulna, Colles' fracture, arthritic spurs, tumor, or thickening of the transverse carpal ligament.
Conditions that may increase the volume of the contents of the carpal tunnel include fluid retention, fat deposition, carpal synovitis, tenosynovitis, or other space-occupying lesions. Hypothyroidism, as mentioned above, may seem like an odd addition to this list. However, it is considered an important causative factor for CTS because a low functioning thyroid can contribute to "[e]xcess deposition of glycosaminoglycans, hyalauronic acid and some mucopolyssacharides in subcutaneous tissues ... [i]n the narrow space of carpal tunnel, deposition of pseudo mucinous substances on the median nerve sheath leads to compression of the nerve and leads to CTS".(3)
Often the cause for CTS may not be identified by conventional practitioners, who may be only considering the gross structural environment without regard for finer contributing factors. Within these cases, some researchers have found decreased vitamin B6 levels,(4,5) while others have seen evidence of collagen dysplasia with an accumulation of disorganized connective tissue within the transverse carpal ligament.(6) Yet another contributing cause of CTS may be inflammation of the outer layer of the affected connective tissue itself. Some researchers have determined that this outer layer, the 'epineurium', plays a role in nerve regeneration, as well as nerve entrapment.(7) and other researchers have summized that idiopathic CTS is often characterized by severity-correlated enlargement of the median nerve and not by compressive deformation coming down upon it.(8)
Traumatic injury and occupational injury through repetitive use are often considered the most obvious causes of CTS. However, other types of injury to the wrist, via inflammation, excess fat and adipose tissue or nerve tissue impairment, are also factors. Thus documented risk factors include being overweight or obese, smoking, wrist injury, diabetes mellitus, hypertension, hypothyroidism, and rheumatic disease.(1) Yet other studies identified risk factors as repetitive activities with a flexed or extended wrist, hysterectomy without oophorectomy, and last menstrual period in menopausal women 6-12 months earlier.(6-9) Others have found an increased incidence in pregnant women, typically occurring around the third trimester(10) Lastly, both gender and age are also factors, as CTS is more prevalent among women and occurs frequently between the ages of 40 and 60 years.(1)
Symptoms of Carpal Tunnel Syndrome
As mentioned above, most commonly a person experiences pain and tingling or numbness in the hand or wrist. Symptoms are often worse at night and often awaken the patient. People may state that relief is gained from attempts to alleviate the experienced nerve compression, such as shaking or rubbing the hand (or hands if the condition is bilateral). Less commonly a person may complain of clumsiness due to an inability to hold or feel an object.
Examination often reveals impaired sensation in the distribution of the median nerve. If the condition has existed for a prolonged period, atrophy at the base of the thumb and weakness of the thumb abductor are also present.
A physician may also ask a patient to perform different in-office focused physical exams, including Tinel's, Phalen's, and reverse Phalen's tests, which have been the accepted tests for diagnosing CTS in the general office.
Tinel's sign is tingling in the distribution of the median nerve when tapping the nerve in the middle of the palm over the transverse carpal ligament. Phalen's test is positive when symptoms are reproduced by holding the wrist in forced flexion for 60 to 90 seconds. Reverse Phalen's test is described as numbness and tingling produced by forcibly extending the wrist and applying pressure over the median nerve.
Other in-office assessments include a self-administered hand diagram on which the patient draws a pattern of his or her pain, numbness, and tingling (11) as well as subjective assessment of swelling the hand and palpitation of the hand and wrist. In a single-blind, randomized study of 186 patients, continuing subjective swelling during treatment with splinting of the wrist correlated with a poorer clinical response.(12)
Other Diagnostic Tests
Electromyography (EMG) is a diagnostic procedure to assess the health of muscles and the nerve cells that control them. EMG may help confirm compression of the median nerve in the carpal tunnel. Nerve conduction velocity is normal from the elbow to the wrist and diminished from the wrist to the hand and fingers (diminished across the carpal tunnel). Both sensory and motor nerve conduction velocities are measured.
More recently, magnetic resonance imaging (MRI) and high-definition ultrasound imaging have been used in the diagnosis of CTS. With these techniques it is possible to measure the size of the median nerve, as well as the interior dimensions of the carpal tunnel. These imaging methods have also found their way into the preoperative assessment of CTS to evaluate the most appropriate approach to surgery.(13-16)
Check our next blog for information about natural medicine therapies for CTS. Given that the average cost of a surgery for CTS is $4,000 - $12,000, you won't want to miss it!(17)
Pratt NE. Clinical musculoskeletal anatomy. Philadelphia: Lippincott, 1991:14
Elite Insurance Partners LLC d/b/a MedicareFAQ. https://www.medicarefaq.com/faqs/does-medicare-cover-carpal-tunnel-syndrome-surgery/ Accessed on 08-01-2022.
The content and any recommendations in this article are for informational purposes only. They are not intended to replace the advice of the reader's own licensed healthcare professional or physician and are not intended to be taken as direct diagnostic or treatment directives. Any treatments described in this article may have known and unknown side effects and/or health hazards. Each reader is solely responsible for his or her own healthcare choices and decisions. The author advises the reader to discuss these ideas with a licensed naturopathic physician.