Carpal tunnel syndrome (CTS) is the most common peripheral nerve entrapment neuropathy, affecting approximately 3-6% of the adult population. It occurs when the median nerve -- which carries sensation and motor signals to the thumb, index finger, middle finger, and the radial half of the ring finger -- is compressed as it passes through the carpal tunnel, a narrow fibro-osseous passage at the base of the wrist.
The condition is broadly familiar -- most people have heard of it, and many with hand symptoms wonder whether CTS is the explanation. The characteristic presentation is unmistakable to a trained clinician: numbness and tingling in the thumb and first two or three fingers, with symptoms that are typically worse at night and that wake patients from sleep. What is less well understood is that CTS exists on a spectrum from mild to severe, that it is progressive without treatment, and that in advanced cases the nerve damage may not fully reverse even after successful surgery.
The Carpal Tunnel and the Median Nerve
The carpal tunnel is a narrow canal approximately 2.5 cm wide, formed at the base of the palm. Its floor and sides are formed by the carpal (wrist) bones, arranged in an arch. Its roof is the flexor retinaculum, a thick, unyielding fibrous band that spans across the carpal bones, completing the tunnel.
Running through this tight space are nine flexor tendons (which bend the fingers and thumb) and the median nerve. Because the tunnel is bounded on three sides by bone and on one side by a rigid ligament, there is very limited capacity for expansion. Any process that reduces the available space -- inflammation, swelling, structural abnormality, or increased tendon bulk -- compresses the median nerve, which is the softest and most pressure-sensitive structure in the tunnel.
The median nerve provides:
- Sensory supply: the palm surface of the thumb, index finger, middle finger, and the radial (thumb) half of the ring finger
- Motor supply: the muscles of the thenar eminence (the fleshy mound at the base of the thumb) -- specifically the abductor pollicis brevis, opponens pollicis, and flexor pollicis brevis -- which control thumb opposition and grip
The little finger is supplied by the ulnar nerve and is NOT affected in typical CTS, involvement of the little finger in an apparently CTS presentation should prompt consideration of an alternative or additional diagnosis.
Symptoms of Carpal Tunnel Syndrome
Classic symptoms
- Numbness and tingling in the thumb, index finger, middle finger, and the thumb-side half of the ring finger.
- Pain in the hand and wrist, sometimes radiating up the forearm to the elbow. Less commonly to the shoulder.
- Night symptoms, one of the most characteristic features of CTS. Patients wake from sleep with numb, tingling, or painful hands and typically find relief by shaking the hand vigorously or hanging the arm over the edge of the bed.
- Symptoms worsened by activities that flex or extend the wrist: driving, holding a phone or book, cycling, or performing overhead tasks.
Symptoms of more advanced CTS
- Weakness of grip: Difficulty opening jars, turning keys, or holding small objects
- Dropping objects: Particularly when not consciously aware of the weakened grip
- Clumsiness with fine tasks: Buttoning clothing, picking up small items, writing
- Difficulty distinguishing hot from cold with the affected fingers
Causes and Risk Factors
CTS occurs when anything reduces the space available for the median nerve within the carpal tunnel. The underlying mechanism is cumulative nerve compression causing ischaemia (reduced blood flow) and, over time, structural nerve damage.
Structural and anatomical causes
- Smaller carpal tunnel size: A constitutional anatomical factor; explains why CTS runs in families and why some individuals develop CTS with minimal external contributing factors
- Wrist fracture or dislocation: A Colles' fracture or other wrist injury can cause bony deformity that narrows the tunnel acutely or chronically
- Ganglion cyst or lipoma within the carpal tunnel: Space-occupying lesion compressing the nerve
Inflammatory and systemic conditions
- Rheumatoid arthritis: Inflammation around the joints and tendons increases pressure within the carpal tunnel.
- Diabetes mellitus: Peripheral neuropathy from diabetes can predispose to and worsen nerve compression at the wrist; CTS is significantly more common in people with diabetes
- Hypothyroidism: Fluid buildup in the tissues increases pressure in the carpal tunnel, and carpal tunnel syndrome may be an early sign of an underactive thyroid./li>
- Pregnancy: Fluid retention and hormonal changes increase pressure in the carpal tunnel, causing carpal tunnel syndrome that usually resolves after delivery.
Occupational and lifestyle factors
- Repetitive hand and wrist use: Particularly tasks involving repetitive flexion and extension, vibrating tools, or sustained grip
- Prolonged wrist flexion or extension: Keyboard use, driving, or any occupation requiring sustained wrist deviation
- Vibrating hand tools: Power tools, jackhammers, heavy machinery
- Assembly line work: Repetitive, forceful pinch or grip
Risk factors
- Female sex: CTS is 2-3 times more common in women; hormonal influences and smaller carpal tunnel dimensions are contributing factors
- Age 40-60: Peak incidence age range; CTS is uncommon in young adults without a systemic cause or significant occupational exposure
- Obesity: Increased body mass index is associated with increased carpal tunnel pressure
- Family history: Constitutional carpal tunnel size has a hereditary component
- Dominant hand: Typically affected first and more severely
Differential Diagnosis: What Else can Mimic Carpal Tunnel Syndrome
Several conditions cause hand numbness that may be mistaken for CTS. An accurate diagnosis is important because the treatment for each is different. The following conditions should be considered and excluded:
- Cubital tunnel syndrome (ulnar nerve compression at the elbow): Causes numbness in the little finger and the ulnar (little-finger) side of the ring finger, plus weakness of intrinsic hand muscles. The little finger is the key differentiator from CTS.
- Cervical radiculopathy (neck nerve root compression): Compression of a nerve in the neck causes numbness, neck pain, and symptoms that change with head or neck movement. C6 nerve root compression can mimic carpal tunnel syndrome.
- Thoracic outlet syndrome: Compression of nerves or blood vessels between the neck and shoulder causes symptoms affecting the whole hand or the little finger side of the hand, which worsen with certain arm positions.
- Pronator teres syndrome: Compression of the median nerve in the forearm causes symptoms similar to carpal tunnel syndrome but is associated with forearm tenderness, no night symptoms, and normal nerve conduction at the wrist.
- De Quervain's tenosynovitis: Causes pain at the thumb side of the wrist rather than numbness and is associated with a positive Finkelstein's test.
- Peripheral neuropathy (diabetic or other): Usually affects both hands, involves all fingers, and is often associated with diabetes or other conditions affecting the nerves.
How Carpal Tunnel Syndrome is Diagnosed
- Clinical History and Examination: Assesses the pattern of symptoms, factors that trigger them, and their effect on hand function. The examination evaluates sensation, hand strength, and thumb muscles. Involvement of the little finger suggests a diagnosis other than carpal tunnel syndrome.
- Phalen's Test: The patient holds both wrists fully bent for 60 seconds. Reproduction of tingling or numbness in the median nerve distribution suggests carpal tunnel syndrome, especially when combined with Tinel's sign.
- Tinel's Sign: Tapping over the median nerve at the wrist causes tingling or numbness in the median nerve distribution, suggesting carpal tunnel syndrome.
- Ultrasound: Examines the median nerve for swelling or compression and can detect structural causes such as cysts. It is useful when nerve conduction studies are inconclusive or not tolerated.
- Electromyography: Checks for nerve damage in the thumb muscles. Evidence of significant nerve damage suggests severe carpal tunnel syndrome and supports the need for surgery.
- Blood Tests: Look for underlying conditions, such as hypothyroidism, diabetes, rheumatoid arthritis, or kidney disease, that may contribute to carpal tunnel syndrome.
Preventing Carpal Tunnel Syndrome
Though there are no definite, proven ways to prevent carpal tunnel syndrome, you can lessen stress on the hands and wrist with these methods:
- Take short, frequent breaks: Gently stretch and bend your hands and wrists from time to time. Taking a break for even a few minutes every hour can make a difference.
- Watch your form: Avoid bending your wrist all the way up or down when using a keyboard. Let your wrists rest on the desk in a neutral position, with your wrists in line with the floor.
- Use ergonomic equipments: Use an ergonomic mouse or mousepad to avoid straining your wrist.
