Radial Mononeuropathy - Causes, Symptoms, Diagnosis, and Treatment

Introduction:

The radial nerve is one of the major nerves of the upper limb that innervates the muscles and the joints in the back portion of the upper arm and the forearm. In addition, the radial nerve carries the sensory signals from most of the overlying skin in the backhand. The radial nerve originates from the brachial plexus (a network of nerves present in the shoulder), descends down the spiral groove of the humerus (a long bone of the arm), and branches out along the length of the upper limb. Most of the muscles innervated by radial nerves are extensors (which help in stretching the forearm).

What Is Radial Mononeuropathy?

Mononeuropathy refers to the damage or injury of a single nerve that results in the dysfunction of that particular nerve. Therefore any injury to the radial nerve is termed radial mononeuropathy. The loss of radial nerve function will reflect a significant disability in the upper arm.

Based on the location of the injury, radial mononeuropathy can be classified as high and low radial nerve palsy with different clinical presentations.

• High Radial Nerve Palsy - Injury to the radial nerve proper above the half forearm.

• Low Radial Nerve Palsy - Injury to the radial nerve branches below the half forearm.

The prevalence of radial mononeuropathy is more common in trauma secondary to fractures.

What Are the Causes of Radial Mononeuropathy?

The following are some of the causes that injure the radial nerve,

• A humerus fracture is one of the leading causes of radial mononeuropathy, particularly in the Holstein-Lewis fracture, where the humerus is fractured at the lower one-third near the elbow. The radial nerve is jeopardized as the nerve is closely opposed to the bone.

• Abnormal bony growth of the humerus.

• Elbow joint dislocation.

• Loss of blood supply caused by thermal injury, electric shock, or radiation.

• Compression of the nerve in infection or inflammation.

• Vigorous physical activity compresses the muscles overlying the radial nerve.

• Entrapment of the nerve due to any tumor or deformity in the structure.

• Tight pressure from the cast or braces.

Sometimes radial nerve dysfunction is transient and popularly described under various terms based on the causative situation. They are,

• Saturday Night Palsy: Excessive alcohol can be a factor, and the condition occurs by falling asleep with one’s arm hanging downwards from the backrest of the chair, squeezing the radial nerve.

• Honeymoon Palsy: Overnight compression of one’s arm by another person sleeping over it.

• Handcuff Neuropathy: Tightly secured handcuff may pinch one of the branches of the radial nerve near the worst junction.

• Crutch Palsy: Caused by the improper use of walking aids, especially axillary crutches.

• Squash Palsy: A sports injury caused by traction force, commonly occurring in squash players after long matches.

How Does Radial Mononeuropathy Develop?

The injury to the radial nerve results in the degradation of the connective tissue layers of the nerve. There are three connective tissue layers named,

1. Endoneurium: Innermost layer.

2. Epineurium: Outer layer.

3. Perineurium: Layer between the endoneurium and the epineurium.

Sydney Sunderland classified the intensity of the nerve damage based on the extent of injury to the connective tissue layers as,

• Type 1 - First Degree: Neuropraxia - Mild injury usually healing on its own.

• Type 2 - Second Degree: Axonotmesis - More than a minor insult and spontaneous recovery can occur after a few weeks.

• Type 3 - Third Degree: Type 2 plus endoneurium injury.

• Type 4 - Fourth Degree: Type 3 plus perineurium injury.

• Type 5 - Fifth Degree: Type 4 plus epineurium injury (neurotmesis - complete transection).

What Are the Signs and Symptoms of Radial Mononeuropathy?

The clinical findings of radial mononeuropathy depend on the severity and the location of the injury. Usually, patients with radial mononeuropathy always try to hold or support their affected arm with the unaffected normal hand, and they may have the following symptoms,

• Pain and tenderness.

• Difficulty in stretching the hands.

• Unusual sensations like numbness, tingling, or burning.

• Imbalance.

• Muscle cramps.

• Abnormal response to stimulation.

• Excessive sweating.

• Heat intolerance.

How to Diagnose Radial Mononeuropathy?

Radial nerve injury has specific signs and symptoms that make it easy to know how and where the injury has occurred. However, the following methods are used for the definitive diagnosis of radial mononeuropathy.

1. History and Physical Examination: The physician may enquire about the situation and the time from when the symptoms started and check for the stretching ability of the upper limb. Skin sensation and reflex to stimuli are evaluated. The mechanical function of the radial nerve can be tested by extending the thumb against resistance, and the sensory function can be checked by the discrimination of two separate points when touched by an object at the back side of the thumb.

2. Nerve Conduction Study (NCS): The electrical activity of the skeletal muscle can be recorded and evaluated, which is called the nerve conduction study. The technique is also termed electromyography (EMG). In addition, EMG helps in comparing the treatment outcome.

3. MRI (Magnetic Resonance Imaging): Mostly, normal X-rays are adequate in evaluating fracture-related radial nerve injury. However, MRI images can give details of compressive neuropathies.

4. Ultrasound: Recently, ultrasonography has been used in the diagnosis of radial nerve entrapment in the spinal groove.

How to Treat Radial Mononeuropathy?

Based on the severity, the following treatments can be prioritized.

Conservative Management:

• Localized symptoms can be relieved by taking painkillers and muscle relaxants.

• Steroid shots help in reducing inflammation.

• Physiotherapy to improve the range of motion and regain muscle strength.

• Casting or bracing (a technique to apply a supporting device to the injured area) to promote spontaneous healing.

Surgical Management:

Surgery is preferred only when conservative management fails to resolve the symptoms. The area under which the nerve is pinched is incised to relieve the overlying pressure.

Conclusion:

Most patients with radial mononeuropathy feel better once the causative factor is identified and treated accordingly. The healing of the nerve depends on the age, risk factors, and overall health of the person. The treatment plan is customized specifically for each individual based on their symptoms and cause. Patients’ compliance and adherence to follow-up appointments will give a good treatment outcome.