Carpal tunnel syndrome

Carpal tunnel syndrome (CTS) is a common nerve compression syndrome. It occurs when the median nerve is squeezed within the carpal tunnel of the wrist.

This condition is significant because it is the most common nerve compression syndrome. It is estimated to affect one out of ten people during their lifetime. Most cases are idiopathic, meaning they have no known specific cause. When the syndrome affects both wrists, it is known as bilateral CTS. Understanding this condition helps us see how pressure affects our nervous system.

The carpal tunnel is an anatomical compartment at the base of the palm. It is located in the middle third of the palm's base. The tunnel is bounded by carpal bones that form an arch. On the anterior surface, a strong fibrous band called the transverse carpal ligament covers the tunnel.

Nine flexor tendons and the median nerve pass through this tight space. The median nerve provides sensation to the thumb, index, middle, and half of the ring finger. It also supplies the muscles at the base of the thumb. These muscles allow the thumb to abduct, or move away from the other fingers.

Compression happens when the pressure inside this compartment increases. This pressure can interfere with the normal blood flow inside the nerve. The severity of the damage often follows a dose-response curve. This means longer or greater periods of pressure lead to more nerve dysfunction. For a person with normal blood pressure, symptoms may begin at approximately 39mm Hg of pressure. In contrast, CTS patients often have elevated pressures between 12 and 31mm Hg.

Wrist movements like flexion or extension can raise tunnel pressure as high as 111mm Hg.

Nerve injury can occur in several distinct stages. Most patients experience degree I injury, also called neuropraxia. This involves a conduction block and segmental demyelination, which is the loss of the nerve's protective coating. If the pressure is relieved, the nerves can remyelinate and recover. However, severe cases may result in degree II or III injuries, known as axonotmesis. In these cases, the axon itself is injured. This can lead to muscle weakness or atrophy, which is the shrinkage of muscle tissue.

Symptoms typically include numbness, tingling, or burning sensations. These sensations affect the thumb and most of the fingers. Many people find these symptoms are most troublesome at night. This often happens because people sleep with their wrists bent.

Wearing a wrist splint can help by keeping the wrist straight. If left untreated for years or decades, CTS can cause a loss of sensitivity. It can also lead to the atrophy of the thenar muscles at the base of the thumb.

Many factors are associated with the development of CTS. Genetics are believed to be one of the most important determinants. A genome-wide association study identified 50 genomic loci associated with the disease. Other risk factors include being female, obesity, diabetes, and thyroid disease. One study noted that obese individuals are 2.5 times more likely to be diagnosed. Work-related factors like repetitive strain, vibration, and hand force are also risk factors.

Diagnosis is often made through characteristic symptoms and signs. Doctors can also use electrodiagnostic tests to measure nerve function. While corticosteroid injections may alleviate symptoms, they may not sustainably change the disease. Surgery is the only known disease-modifying treatment. During surgery, a doctor cuts the transverse carpal ligament to increase the space.

This procedure aims to reduce the pressure on the median nerve and prevent further damage.