Carpal Tunnel Syndrome - Pt 1

Throughout the continental United States, the first full week of May each year is observed as Peripheral Neuropathy Week. This year it ran from May 4-11. The goal is to bring public awareness to a condition that is estimated to affect about 2.4 per cent of the global population, with prevalence increasing to five to seven per cent in those age 45 and older.

Peripheral neuropathy, often abbreviated to neuropathy, refers to damage or disease affecting the nerves outside the brain or spinal cord and may affect a single nerve (focal or mononeuropathy) or many nerves (polyneuropathy). Focal neuropathies may result from compression, entrapment, stretch injury, impaired blood supply, direct trauma, fracture or dislocation or other processes. Compression and entrapment neuropathies are among the commonest disorders encountered in electrodiagnostic medicine.

The term compression and entrapment are often used more or less interchangeably, sacrificing some accuracy. Compression neuropathy refers to nerve damage due to applied pressure to a nerve, irrespective of the source; the term entrapment neuropathy is appropriate when the pressure is exerted by an anatomical structure as the nerve travels through narrow anatomical spaces.

All entrapment neuropathies are compression neuropathies, but not all compression neuropathies are due to entrapment.

CAUSES, SYMPTOMS, DIAGNOSIS & TREATMENT

Carpal tunnel syndrome (CTS) is recognised as the most common entrapment neuropathy. It occurs at the wrist, as the median nerve crosses from the distal forearm to the hand through the carpal tunnel.

The walls and floor of the tunnel are formed by the carpal bones and the roof by the transverse carpal ligament (f lexor retinaculum), a strong fibrous band that runs across the palmar side of the hand at the wrist. Lying with the median nerve in the tunnel are the tendons of three forearm muscles, surrounded by a complex protective sleeve surrounding the tendons (synovial sheath). The synovial sheath contains (synovial) fluid which lubricates the tendons and reduces friction during movement.

Most cases of CTS can be attributed to either reduced space within the tunnel (as occurs in inflammatory/degenerative joint diseases like rheumatoid arthritis,osteoarthritis), susceptibility of the nerve to pressure (as occurs in diabetes, pre-existing polyneuropathy) or associated with other conditions (e.g. pregnancy, thyroid disease, chronic kidney diseases, and patients undergoing dialysis).

CTS can be an occupational disease, meaning it can be caused or worsened by work-related factors. Work tasks/occupations involving repetitive movements, forceful gripping or the use of vibrating tools can increase the risk of developing CTS. Such occupations include office workers (especially those who type extensively), musicians, mechanics and assembly line workers.

CTS produces a characteristic clinical picture of hand pain, numbness, and tingling (all invariably more severe at night), along with varying degrees of hand weakness.

The median nerve is responsible for sensation in the thumb, index, middle and half of the ring finger, so complaints of tingling and/or numbness are typically experienced in these fingers. However, many patients report that the entire hand falls asleep, but if asked directly about involvement of the little finger, most will subsequently note that the little finger is spared.

It is useful to note that pain, typically localised to the wrist, may radiate proximally to the forearm, arm or rarely the shoulder; some individuals describe a diffuse, poorly localised ache involving the entire arm. The dominant hand is more frequently affected in CTS.

While bilateral involvement is common, both clinically and electrodiagnostically, and both hands may eventually be affected, the dominant hand tends to be the first and/or more severely affected.

Patients in whom CTS predominantly affects the non-dominant hand are distinctly unusual and should strongly suggest a specific underlying cause that is not simply resulting from overuse and “wear and tear”. All studies indicate that women are two to three times more likely to develop CTS. Symptoms are often provoked when either a flexed or extended wrist posture is assumed. Most commonly, this occurs during ordinary activities, such as driving a car or holding a phone, book or while reading a newspaper.

During sleep, persistent wrist flexion or extension leads to increased pressure within the tunnel and reduced blood flow to the nerve. Patients frequently awaken from sleep and shake or wring their hands or hold them under warm running water to obtain temporary relief.

GOLD STANDARD

The diagnosis of CTS should be based on patient history, physical examination and results of electrophysiological tests (nerve conduction studies/NCS). These electrophysiological tests will usually detect more than 95 per cent of cases of CTS when meticulously performed. While NCS remains the gold standard for diagnosis, high frequency ultrasonography (HFUS) has been validated to be a useful, non-invasive and portable tool in certain situations.

The best treatment approach for CTS will depend on the individual’s specific symptoms, the severity of the condition, and other factors.

A variety of non-surgical treatment options exist but carpal tunnel release surgery is usually required when non-surgical options have failed to alleviate severe or persistent symptoms or when there is unequivocal evidence of nerve damage.

The latter may include significant weakness, constant numbness or muscle wasting (atrophy) in the hand. This type of surgery is performed through an open incision in the palm of the hand or through a smaller incision using a minimally-invasive technique with an endoscope.

Dr. Daniel S. Graham, OD, MD, FACP is a consultant in clinical neurology, diplomate, American Board of Neurology and Fellowship trained in Neurophysiology and Neuromuscular Diseases. He is the Medical Director of Neurodiagnostics Limited, Centre for Electrodiagnosis of Neurological Disorders.