What Is It, Causes, Treatment, and More
Author: Nikol Natalia Armata
Editors: Ahaana Singh, Ian Mannarino, MD, MBA
Copyeditor: Joy Mapes
Illustrator: Jillian Dunbar
What is mononeuropathy?
Mononeuropathy refers to the damage or dysfunction of a single peripheral nerve, which includes any cranial nerve, spinal nerve, or nerve branch that connects the central nervous system (i.e., the brain and spinal cord) to the entire body. Most mononeuropathies cause both motor and sensory impairment, usually affecting the hands, arms, or feet.Two of the most common mononeuropathies are cubital tunnel syndrome and carpal tunnel syndrome. Cubital tunnel syndrome refers to neuropathy of the ulnar nerve, which is responsible for sensation in the fourth and fifth fingers (i.e., ring finger and little finger, respectively), as well as part of the palm and the underside of the forearm. Carpal tunnel syndrome, however, refers to neuropathy of the median nerve, which is responsible for sensation in the first (i.e., thumb), second (i.e., index finger), third (i.e., middle finger), and fourth fingers. Another common neuropathy is peroneal nerve dysfunction, which affects the peroneal nerve, a branch of the sciatic nerve that provides movement and sensation to the lower leg, foot, and toes.
What is the difference between mononeuropathy and polyneuropathy?
The main difference between mononeuropathy and polyneuropathy is that mononeuropathy refers to damage of a single nerve, whereas polyneuropathy refers to damage of multiple nerves. Both, however, are types of peripheral neuropathy. The accumulation of multiple mononeuropathies, known as mononeuritis multiplex, may at times be difficult to differentiate from polyneuropathy.
What causes mononeuropathy?
For most mononeuropathies that have an acute presentation, the underlying cause may be difficult to define since they often resolve rapidly and provide no opportunity for a complete examination. Nonetheless, mononeuropathies are usually the result of local nerve damage caused by compression-related events that are classified as either fixed or transient.
Fixed mononeuropathies are mainly induced by nerve compression against a hard surface, such as a tumor, cast, or even a prolonged cramped posture (e.g., during hospitalization or surgery). As a result, there may be a change in sensation, and sometimes, in movement, of the affected area. Fixed mononeuropathies usually affect superficial nerves like the radial nerve, which extends along the forearm, or the peroneal nerve, which extends into the lower leg. Fixed mononeuropathies are more often noticed in very thin people, as the direct compression of nerves against bones can lead to the condition.
The continuous pressure that causes fixed mononeuropathies can progressively thin the myelin sheath, the protective cover of the nerve, through a process called segmental demyelination. If the pressure is persistent, it may cut through the myelin sheath and injure the nerve axon. This is referred to as Wallerian degeneration, and it can also occur due to local injury, like a deep cut through a nerve.
Additionally, the entrapment of nerves in narrow anatomical spaces can cause fixed mononeuropathies. For example, carpal tunnel syndrome describes when the median nerve is trapped, and cubital tunnel syndrome is when the ulnar nerve is trapped. Multiple risk factors can lead to the entrapment of a nerve in a restricted anatomical structure, including pregnancy and hypothyroidism (i.e., low levels of thyroid hormones), as well as rheumatoid arthritis, which causes swelling and stiffness of the affected joints.
Contrary to fixed mononeuropathies, transient mononeuropathies are triggered by repetitive actions that cause trauma, like aggressive muscular activity or sudden overextension of a muscle.In some cases, mononeuropathies can be linked to non-compression related causes. Sometimes, exposure to cold or radiation may cause damage to a single nerve. Infections localized to an individual nerve, like herpes zoster, can also lead to mononeuropathy. Rarely, early HIV infection can cause mononeuropathy expressed as facial palsy, which usually improves spontaneously.
What are the signs and symptoms of mononeuropathy?
The clinical presentation of mononeuropathy mainly depends on its underlying cause and the particular nerve that is impacted. In most cases, however, all sensory and motor symptoms are typically associated with the single nerve that is affected. Some clinical presentations of mononeuropathies can be abrupt and very painful, while others may present gradually and intensify over time. Transient mononeuropathies show symptoms that are evident only with the motion that originally damaged the nerve, whereas the symptoms of fixed mononeuropathies are more persistent.
Oftentimes, individuals with mononeuropathy complain about changes in sensation, numbness, and paresthesia, a tingling sensation that feels like pins and needles in their feet or hands. Mononeuropathy can also cause pain, experienced as a stabbing or burning sensation. In rare instances, individuals with mononeuropathy may experience complete sensory loss.Motor symptoms, which include any changes related to movement, are frequently present with mononeuropathies. These symptoms include muscle weakness or atrophy, the loss of muscle mass of the affected area. Similarly, loss of coordination between limbs can be noticed. Advanced nerve damage may progress to reduction or loss of tendon reflexes, meaning that the muscles do not contract immediately after the tendon is tapped.
How do you diagnose mononeuropathy?
When diagnosing mononeuropathy, a review of medical history and physical examination, including extensive neurological assessment, are necessary. Consideration of symptoms and examination findings may suggest specific mononeuropathies, but if the clinical diagnosis is inconclusive, further investigation is needed. Electrodiagnostic testing, a method of evaluating the electrical activity of muscles and nerves, is often suggested to help reveal conditions that cannot be detected with physical examination alone. This method also offers the ability to localize the nerve injury, assess its severity, and estimate the prognosis.
How do you treat mononeuropathy?
To treat mononeuropathy, it is important to diagnose and treat its underlying cause. For most mononeuropathies that present with mild symptoms, symptoms can often resolve with adequate rest, application of heat, avoidance or removal of the causative activity, and moderate use of nonsteroidal anti-inflammatory drugs (NSAIDs). In certain circumstances, immobilizing the affected area with medical equipment, such as splints or braces, may improve symptoms. In addition, oral or injected corticosteroids and therapeutic ultrasounds may be suggested in order to reduce pain, increase circulation, and improve mobility. The newest treatment used to relieve carpal tunnel syndrome is hydrodissection under ultrasound guidance, a non-surgical procedure that relieves tension by using a solution to separate the affected nerve from the surrounding tissues.
In the case that conservative treatments are unable to resolve the associated condition, surgical decompression may be required. For instance, when external pressure is applied by a tumor to a nerve, surgery is the only way to relieve any symptoms. Notably, surgical procedures should also be considered in cases where progression of a mononeuropathy occurs despite conservative treatment.
What are the most important facts to know about mononeuropathy?
Mononeuropathy refers to the damage of a single nerve that connects the brain and spinal cord to the entire body. It usually occurs in more superficial branches of the nerves and is seen most often in the hands and legs. Mononeuropathies are mostly caused by compression-related events, and these can be either fixed or transient, but there are causes of mononeuropathies that are not compression related. Individuals with mononeuropathy present with both sensory (i.e., numbness, pain, tingling) and motor (i.e., weakness, atrophy) symptoms that often are characteristic of the cause of injury and can lead to diagnosis. Clinical evaluation is necessary, but if inconclusive, electrodiagnostic testing is suggested. Treatment largely depends on the underlying cause and may be conservative in mild cases. In more severe cases in which conservative treatments do not resolve the symptoms, surgery may be required.
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Resources for research and reference
Fauci, A., & Harrison, T. (2009). Harrison's manual of medicine (17th ed.). New York: McGraw-Hill Medical.
Hammi, C., & Yeung, B. (2020, November 17). Neuropathy. In StatPearls [Internet]. Retrieved from https://www.ncbi.nlm.nih.gov/books/NBK542220/
Peripheral neuropathy. (2019, April 24). In NHS: Health A to Z. Retrieved December 14, 2020, from https://www.nhs.uk/conditions/peripheral-neuropathy/
Rubin, M. (2020, December). Mononeuropathies. In MSD manual: Professional version. Retrieved December 14, 2020, from https://www.msdmanuals.com/professional/neurologic-disorders/peripheral-nervous-system-and-motor-unit-disorders/mononeuropathies
Simon, R., Greenberg, D., & Aminoff, M. (2018). Clinical Neurology (10th ed.). New York, NY: McGraw-Hill Education.