Before looking at how median nerve injuries are diagnosed it’s useful to look at what the nerve does, how it gets injured, and the associated symptoms.
Symptoms associated with a median nerve injury include:
What is The Median Nerve?
The median nerve is in the arm and it originates from the brachial plexus. The nerve runs from the shoulder, down the arm and towards the wrist. The median nerve then passes through the carpal tunnel and enters the hand.
The median nerve controls muscles in the forearm and it’s responsible for some hand movement, too. The nerve innervates the skin of the thumb and the first three fingers which are the index, middle, and ring fingers.
Two conditions associated with a median nerve injury are median nerve palsy and carpal tunnel syndrome.
Median Nerve Palsy
Median nerve palsy is a condition caused by a penetrating injury to a part of the arm or wrist. In some cases, a blunt trauma to the upper arm, forearm, or wrist also causes damage to the median nerve.
Patients with median nerve palsy develop symptoms including a loss of feeling in the digits. The thenar muscles may suffer paralysis which affects hand and finger mobility. Weakness in the forearm is another symptom of median nerve palsy.
Median nerve palsy can be treated with tendon transfers to ease the symptoms and restore motor function. A tendon transfer replaces a damaged muscle and tendon with healthy ones.
Carpal Tunnel Syndrome
Carpal tunnel syndrome (CTS) is a condition that develops when the median nerve is compressed. The condition is common and symptoms include numbness and pain in the forearm and hand. CTS causes tingling or pins and needles in the fingers and the arm.
The symptoms associated with carpal tunnel syndrome develop over a period of time and early diagnosis is important. If the condition remains undiagnosed then permanent damage to the median nerve is a possibility. If the median nerve is permanently damaged then quality of life is affected.
There are various treatments for carpal tunnel syndrome including wearing a wrist brace or splint. Anti-inflammatory drugs are used to take pressure off the median nerve and corticosteroid injections also help.
If non-invasive treatments do not relieve the symptoms of carpal tunnel syndrome, surgery is an option. Carpal tunnel release surgery can be performed to relieve the pressure on the median nerve. The carpal tunnel is made bigger so that the median nerve is less likely to be compressed.
When a patient has reported symptoms associated with median nerve injury, a physician will carry out a series of neurodiagnostic tests. Due to its length there are various places along the arm where the median nerve can get injured.
At the initial consultation the physician will ask the patient about their symptoms and lifestyle. The physician may ask the patient what type of work they do or whether they do repetitive things that could damage the nerve. A physical examination is carried out and the patient is asked to complete a few simple tasks.
One of the symptoms of median nerve damage is the inability to make a fist. The patient will be asked to make a fist and the physician will check mobility in the hand and fingers. If the patient is unable to make a fist it points to median nerve damage in the upper arm.
Another common symptom is the inability to oppose the thumb or flex the middle and index fingers. The patient may be asked to try and grip an object or remove a bottle top. This lack of mobility in the thumb and fingers is sometimes referred to as the benediction hand.
Another simple test carried out includes the pin prick test to check feeling in parts of the hand or fingers. When the skin is pricked with a small needle and the patient does not feel it, there is possible median nerve damage.
When a diagnosis cannot be made following a physical examination a patient will be referred for imaging tests. Imaging tests are used to look inside the body to check for nerve damage and the potential causes.
Magnetic resonance imaging (MRI) is an imaging test used by physicians when looking for nerve damage. MRI uses radio waves and high powered magnets to produce high resolution images.
Studying a high resolution image helps the physician to make an accurate diagnosis. Medical evidence has concluded that MRI is an effective way to diagnose a number of peripheral nerve injuries.
Computerized tomography (CT) scans are used to look for nerve injuries and the possible causes. A CT scan produces detailed pictures of soft tissue, bones, and nerves inside the body. The scanner takes a series of X-rays so that a cross-sectional image is produced.
A CT scan is an effective way to produce 3D images that are needed to diagnose the cause of nerve damage. A CT scan detects bone damage, ligament damage, and tumors that may be compressing the median nerve. Normal X-rays will not detect a lot of the problems that lead to nerve injuries.
Ultrasound is often used in conjunction with MRI and CT scans when looking for median nerve injuries. Ultrasound is useful for detecting tumors that lead to median nerve compression. Physicians may also want to look at the tissue that surrounds the nerve to check for other problems.
If a patient has suffered a fracture, or when the physician suspects a bone spur is compressing the nerve, an X-ray may be taken. Fractures and bone spurs cause nerve compression which lead to symptoms developing. Although nerves cannot be seen by regular X-ray, the bones and surrounding soft tissue can.
If imaging tests have not detected any damage to the median nerve, there are some neurological tests to be done. These tests check whether the median nerve is functioning as it should.
Electromyography (EMG) is a diagnostic test used by physicians to measure electrical activity in muscles. Tiny needles (electrodes) are inserted into various muscles on the arm and hand. A monitor then records the electrical activity that’s picked up by the electrodes.
The level of activity is assessed by the physician which helps to determine whether the median nerve is injured.
Another test used by physicians is called a nerve conduction study (NCS) which measures the speed of signals sent through the nerve. Two electrode patches are placed on the skin above the median nerve. One patch sends an electrical signal and the second receives it.
The physician looks at how long the electrical impulses took to reach the receiving patch. If the time is deemed too slow it points to median nerve damage and more investigation can be done.
Tinel's sign is a neurological test used by physicians to check and assess nerve damage. Tinel’s sign is particularly useful for diagnosing carpal tunnel syndrome.
The test is done by tapping lightly (percussing) over the median nerve to initiate pins and needles or tingling. If the percussion results in tingling in the thumb or fingers it’s called a positive Tinel’s sign. A positive sign indicates median nerve damage and treatment options are then considered.
Phalen's test is another effective way to diagnose a median nerve injury. The physician will ask the patient to put the elbows on a desk or table and allow both wrists to flex. The dorsal surface of both hands is pushed together and held in position for approximately one minute.
If pain, numbness or tingling is reported by the patient during the test, it indicates compression of the median nerve. Phalen’s test is often the first one used by physicians to diagnose carpal tunnel syndrome.
The two point discrimination test checks the sensory function of the median nerve. Blunt points are placed at two areas of skin to check whether the patient can feel one or two points of contact. The test is usually carried out on one or more fingers.
If the patient does not feel two points then there is a possibility that the median nerve is compressed.
When the physician has diagnosed a median nerve injury the appropriate course of treatment can begin. Non-invasive treatments such as anti-inflammatory drugs, steroids, and physiotherapy are the first courses of action. If these treatments do not work, surgery may be needed to decompress the median nerve.
If the median nerve has been severed or damaged by trauma it can be repaired by end-to-end suturing. Nerve grafting is used to treat severed nerves if end-to-end suturing is not an option.
It’s important that an accurate diagnosis is made when the median nerve is injured so that a suitable treatment is given. Damage to the median nerve affects quality of life and the symptoms are uncomfortable. In most cases, treatment following the correct diagnosis will be successful.