Nerve entrapment syndromes cause discomfort, numbness, and weakness in the arm and hand. These conditions occur when a nerve is compressed or irritated as it travels through a narrow anatomical space. Carpal Tunnel Syndrome (CTS) and Cubital Tunnel Syndrome (CuTS) are the two most frequently diagnosed types of nerve compression. A person can have both simultaneously, but this combined presentation introduces a complexity that requires careful diagnosis.
Understanding Carpal Tunnel and Cubital Tunnel
Carpal Tunnel Syndrome involves the compression of the median nerve as it passes through the carpal tunnel in the wrist. This tunnel is formed by the wrist bones and covered by the transverse carpal ligament. The median nerve controls sensation in a large part of the hand and motor function to the small muscles at the base of the thumb.
Cubital Tunnel Syndrome affects the ulnar nerve at the elbow. Compression occurs as the ulnar nerve travels through the cubital tunnel, a space under the medial epicondyle (the bony bump on the inside of the elbow). This nerve provides sensation to the little finger and half of the ring finger, and controls most of the hand’s small muscles.
Distinct Symptoms and Affected Nerves
Carpal Tunnel Syndrome typically causes numbness, tingling, and pain in the thumb, index, middle, and thumb-side half of the ring finger. These sensations are often worse at night or when the wrist is held in a flexed position, such as when driving or holding a phone.
Cubital Tunnel Syndrome symptoms cause numbness and tingling specifically in the little finger and the little-finger side of the ring finger. This condition frequently causes aching pain along the inside of the elbow and forearm. Symptoms are commonly aggravated by sustained elbow flexion, which stretches the ulnar nerve and narrows the cubital tunnel space.
When Both Conditions Occur Simultaneously
Both Carpal Tunnel Syndrome and Cubital Tunnel Syndrome can occur in the same arm, a situation sometimes referred to as multiple nerve entrapment. This simultaneous compression is a presentation of “Double Crush Syndrome,” where a nerve compressed at one location becomes more vulnerable to compression further down its pathway. The initial compression may disrupt the flow of nutrients along the nerve fiber, making the structure more susceptible to a second injury.
This co-occurrence complicates symptom identification because the numbness and tingling from the median and ulnar nerves can overlap significantly in the hand. Symptoms of one compression may mask or mimic the symptoms of the other, making it difficult to pinpoint the exact source of discomfort. The non-random association means that a patient with one type of nerve entrapment has a greater chance of developing the other.
How Doctors Differentiate Between the Two
When both conditions are suspected, doctors rely on physical examination techniques and objective electrodiagnostic testing to pinpoint the exact location of each nerve compression. Simple clinical tests help identify the likely location of the problem. For example, a doctor may perform Phalen’s maneuver, which involves holding the wrist in forced flexion to increase pressure on the median nerve, provoking CTS symptoms.
For Cubital Tunnel Syndrome, the doctor may use the elbow flexion test, where the elbow is held in a deeply bent position to provoke ulnar nerve symptoms. A Tinel’s sign is also performed by gently tapping over the nerve at the wrist and the elbow; a tingling sensation confirms nerve irritation at that specific site.
Nerve Conduction Studies (NCS) and Electromyography (EMG) are the definitive tools used to differentiate between the two conditions. NCS measures the speed of electrical signals along the median and ulnar nerves, comparing conduction velocity across the wrist and the elbow. Slowing of the signal across the carpal tunnel confirms CTS, while slowing across the elbow confirms CuTS, even when both are present. EMG assesses the electrical activity of the muscles, helping determine the severity of nerve damage and ruling out other potential causes, such as compression higher up in the neck or shoulder.