What is Median Nerve Palsy?
The median nerve is an important nerve in our arm that stems from the middle and lateral cords of the brachial plexus, a network of nerves located in the neck and shoulder area. It receives signals from all roots of the brachial plexus (C5-T1). This nerve goes down the arm, under the ligament of Struthers, the bicipital aponeurosis, and the two heads of pronator teres, and makes its way into the front section of the forearm. If the median nerve gets compressed at this point, it can result in something called pronator syndrome.
Close to your elbow, the median nerve sends out its first terminal branch, called the anterior interosseous nerve (AIN). The AIN travels between the muscles that control finger curling and thumb bending, and eventually ends in the muscle that turns your forearm inwards. This nerve provides signals for muscles that help curl the index and middle fingers, bend the thumb, and turn the forearm inward. An interesting thing to note here is that the half of the finger curling muscle that controls the little and ring fingers is connected by the ulnar nerve.
Another branch of the median nerve, called the palmar cutaneous branch, runs to the hand, and provides feeling to the side of your palm closest to your thumb. This nerve doesn’t go through the carpal tunnel (a narrow passageway in your wrist), which explains why people with carpal tunnel syndrome usually don’t lose sensation in this part of their hand.
After branching off into AIN and the palmar cutaneous branch, the median nerve moves further down between the deeper muscles that assist with finger curling and superficial muscles. It gives signals to all the surface muscles that bend the forearm, while the AIN gives signals to the deeper ones.
The median nerve then enters the hand through the carpal tunnel. The nerve shares this tunnel with four tendons each of the muscles that control finger curling and thumb bending. To treat carpal tunnel syndrome, a doctor may perform a surgical procedure to relieve pressure on the median nerve by cutting a ligament in the wrist.
Once in the hand, the median nerve further divides into two branches, each responsible for specific actions. One controls the muscles at the base of your thumb, except for one muscle that the ulnar nerve controls. The other connects to the fingers, providing signals for sensation and control of specific parts of fingers. A detailed understanding of these nerves allows doctors to accurately identify issues with the median nerve, be it acute—which needs urgent attention—or chronic, requiring a more careful approach. History and physical examination are crucial tools in coming up with the best treatment plan for such conditions.
What Causes Median Nerve Palsy?
Median nerve palsies, which refer to weakened or paralyzed areas caused by damage to the median nerve, can happen due to pressure, stretching, or injuries. To properly care for patients experiencing this, it’s critical to pinpoint the exact cause of the nerve damage through a detailed physical check-up, and if needed, by using advanced diagnostic methods.
Injury to the median nerve can often happen as a result of penetrating wounds to the upper arm. This can cause what’s known as a median nerve palsy. Since the nerve is close to the brachial artery, injuries here can often also damage the artery. If the artery is injured, it may result in a lack of blood flow to the arm, creating a serious situation that needs immediate attention. In some cases, there have been reports of median nerve damage in the upper part of the arm after a test called brachial angiography, which examines the arteries in your arms.
The median nerve can also be squeezed at various places round and near the elbow. This can happen at structures like the ligament of Struthers (a small band of tissue near the elbow) and bicipital aponeurosis (a broad, flat tendon), as well as between the muscles of the forearm known as pronator teres.
Injuries caused by sharp objects between the elbow and the wrist can cut or injure the median nerve, or other nerves in the arm such as the anterior interosseous nerve (a branch of the median nerve) and the palmar cutaneous branches of the median nerve.
Usually, median nerve palsies are due to the nerve being compressed in the wrist, specifically in an area called the carpal tunnel. When it is compressed here, it leads to a condition called carpal tunnel syndrome. Frequently, the symptoms of this can be eased with simple measures, but if needed, the condition often responds well to surgery.
Risk Factors and Frequency for Median Nerve Palsy
Several conditions affect the median nerve, which is an important nerve in your arm and hand. The age, sex, and personal medical history of a person can help identify these conditions.
- Pronator teres syndrome, a condition affecting a muscle in the forearm, typically impacts people around 50 years old. Men are significantly more likely to get this than women.
- Carpal tunnel syndrome, another condition impacting the median nerve, is quite common. It affects about 105 in every 100,000 people each year. Women are three times more likely to get this condition than men.
- Although carpal tunnel syndrome tends to peak in people around 50 years old, it’s also common in the older population.
- People who have diabetes or thyroid disease have a higher risk of developing carpal tunnel syndrome, so doctors will take this into account when diagnosing patients.
Signs and Symptoms of Median Nerve Palsy
If you suspect you have damage to your median nerve (which can cause pain, numbness, and weakness in your hand and arm), doctors will look into how and when your symptoms started and what makes them better or worse. People with diabetes and thyroid disease are at a higher risk for conditions like carpal tunnel syndrome, so doctors will also go over your medical history to better understand your risk.
A physical check-up will focus on spotting any loss of movement or feeling. Your doctor will be looking to see where the issue might be coming from. Often, the problem is due to pressure on the nerve in your wrist (carpal tunnel) or elbow (pronator syndrome). This can be caused by issues like a slipped disk in your neck or blood vessel damage, especially in your upper arm. In severe cases, immediate treatment may be needed to stop permanent nerve damage.
The median nerve is usually pinched where it passes through your carpal tunnel, which is a narrow passageway in your wrist. This nerve is responsible for feeling in the thumb, index, middle, and ring fingers. There’s another branch of the nerve that gives feeling to the palm of your hand, and it’s not usually involved in carpal tunnel syndrome. If you have this condition, you might have weakness around the bottom of your thumb. The doctor may test this by asking you to move your thumb across your palm. The muscles that bend your index and middle fingers should still work as they are powered by a different branch of the median nerve.
There are specific tests that your doctor may do to check for carpal tunnel syndrome such as Phalen’s test and Tinel’s sign. The Phalen’s test involves bending your wrist for 60 seconds to see if it causes symptoms. The Tinel’s sign is done by tapping on your carpal tunnel to see if it causes symptoms in your hand.
- Phalen’s test: Bending your wrist for 60 seconds to see if it causes symptoms
- Tinel’s sign: Tapping on your carpal tunnel to see if it causes symptoms in your hand
Another place where your median nerve might get pinched is at your elbow. This is known as pronator syndrome and it’s often mistakenly diagnosed as carpal tunnel syndrome. A key difference is that pronator syndrome can cause numbness over the palm side of your thumb, which doesn’t happen in carpal tunnel syndrome. A simple test involving extending and rotating your arm can help your doctor tell the difference between the two conditions.
It’s also important to examine the neck in people who may have damage to the median nerve or carpal tunnel syndrome. This is because there can be nerve damage both at the hand and the neck – a condition known as double crush syndrome. People with this syndrome tend to have more “pins and needles” feeling rather than numbness. Also, their grip strength can be more affected compared to those with carpal tunnel syndrome alone. However, scans of the neck like X-rays or MRIs are not normally needed to diagnose this condition. Instead, your doctor would rely on your history and physical examination, using specific tests to identify if nerve compression is happening in your neck.
Testing for Median Nerve Palsy
In any medical scenario, a full physical examination is the most critical step a doctor takes to diagnose issues like median nerve problems. If you’ve had an incident like a fracture or trauma, the doctor may use x-rays to check for associated bone injuries that may harm or pinch the nerve, although x-rays aren’t very helpful for working out nerve injuries themselves.
An ultrasound can be useful in these situations, as it might help find out the cause of nerve compression. Another test commonly used to diagnose nerve compression issues is electromyography (EMG). This test uses small devices called electrodes to translate the electrical signals in your muscles into graphs, sounds, or numerical values that a specialist interprets. When you have a nerve compression issue that this test uncovers, it means you might experience a delayed response time (increased distal latency) and slower signal speed (decreased conduction velocity). If the muscle controlled by the affected nerve starts twitching of its own volition (fasciculations), it’s a sign that it’s losing its nerve supply and more immediate surgical relief could be necessary.
Treatment Options for Median Nerve Palsy
If the median nerve, which runs down your arm and hand, gets seriously injured and there’s a visible cause like swelling from an injury (which doctors call “compartment syndrome”) or a growing pool of blood (an “expanding hematoma”), it often needs quick surgery. This is to stop permanent harm to parts of the muscle that helps it move (called “motor endplate units”). However, for most cases where the median nerve is squashed or compressed, doctors usually try non-surgical treatments first.
A common issue with the median nerve is carpal tunnel syndrome, which is often first treated by wearing a splint at night to keep the wrist straight. If the wrist is bent back too far, it can increase pressure in the “tunnel” in your wrist (known as the carpal tunnel) where the median nerve runs. Another treatment is injections of corticosteroids, a type of medicine that can delay the need for surgery for up to a year. But these injections do have risks, like accidentally injecting into the nerve itself.
A similar condition to carpal tunnel syndrome is called pronator syndrome. It too should be first treated with non-surgical methods after an initial assessment by doctors. Splints and anti-inflammatory medications (drugs that reduce swelling) are the first steps in treatment. If a patient doesn’t get better with these methods and tests confirm they have pronator syndrome, surgeons might consider a surgical release of the structures squashing the nerve. In the elbow area, there can be many things that might be causing the pressure, so surgeons may consider releasing everything that could be causing pressure, like the ligament of Struthers, the lacertus fibrosis, and the fascia of the pronator teres.
What else can Median Nerve Palsy be?
To identify different types of hand nerve injuries, it’s crucial to know the structure and function of the median nerve. This knowledge helps to distinguish its damage from injuries to other hand nerves such as the radial or ulnar nerves. Each of these nerves has particular patterns of sensation and movement they control, which can indicate the injured nerve.
However, sometimes it can be tricky to diagnose these nerve injuries. For instance, cervical radiculopathies might confuse doctors because the median nerve is controlled by nerve roots running from the 5th bone in the neck (C5) to the first bone in the chest (T1), so nerve injuries might be mistaken for those resulting from damage to the nerve roots. Knowing the anatomy of nerve roots can help precisely figure out if the injury is in the nerve root or further down in the median nerve.
Then we have a condition called Parsonage-Turner syndrome, also known as neuralgic amyotrophy. It’s a temporary inflammation of the network of nerves in the shoulder area, called the brachial plexus. Its symptoms begin with a sudden sharp shoulder pain, which is followed by increasing weakness, changes in reflexes, and abnormal sensations, usually after a viral illness. Doctors believe this syndrome is caused by the body’s immune reaction to a viral infection. Sometimes it may be hard to identify the initial cause, but it is critical to consider recent illnesses in the patient’s medical history.
What to expect with Median Nerve Palsy
Patients who have an open carpal tunnel release surgery usually experience significantly improved outcomes, with this improvement seen in 70% to 90% of cases. Surprisingly, diabetes, a risk factor for the development of carpal tunnel, doesn’t seem to affect the results of this surgery.
One study even suggested that patients with “double crush” syndromes, a condition where a nerve is pinched in two places, still saw improvement after carpal tunnel release surgery. In this study, 11 out of 15 patients reported good to excellent results.
For patients diagnosed with pronator teres syndrome, a condition affecting the forearm muscles and nerves, they can typically return to their usual activities within 6 weeks after nerve release. However, if a surgery called “tendon transfers” is needed, the return to normal activities is delayed to about 10 to 12 weeks.
Possible Complications When Diagnosed with Median Nerve Palsy
There’s always a risk of damaging nearby nerves and vessels during any surgical procedure to relieve pressure. A common side effect related to carpal tunnel surgery is unintentional injury to the recurrent motor branch of the median nerve, which controls some of our hand movements. Doctors have found many different natural variations of this nerve, but they typically don’t try to dissect or separate it in surgery. Instead, the general advice is to avoid cutting the ligament in the wrist (transverse carpal ligament) too far to the side of the hand, as this increases the risk of injury to the recurrent motor branch of the median nerve.
- Potential harm to the nerves and blood vessels around the surgery area
- Injury to the recurrent motor branch of the median nerve (controls some hand movements)
- Risk increased when wrist ligament (transverse carpal ligament) is cut too much to the side of the hand
Preventing Median Nerve Palsy
Patients experiencing symptoms like feelings of numbness, a tingling sensation (also known as paresthesias), pain, or weakness in the upper body should consult a medical professional. This is important in order to figure out what’s causing these symptoms and to develop a suitable treatment plan moving forward. For sudden or severe issues, immediate surgery might be necessary, but in most cases, a non-surgical approach is tried first.
