Neuropathy: Classification, Types, Causes, Risk Factors, Symptoms, Treatment, Investigations
Neuropathy commonly refers to dysfunction or diseases of the nerves.
Neuropathies are group of disorders that occur due to some damage to nerves. Any traumatic injuries or diseases like infections, metabolic disorders and exposure to toxins can cause damage to nerves in any part of body resulting in neuropathy.
It is noted that generally it is peripheral nervous system which is mostly affected. This system is located outside of brain.
Neuropathy can affect motor nerves as well as sensory nerves. The motor nerves control movements and sensory nerves control sensations like heat or cold etc.
In some cases like that in autonomic neuropathy, the internal organs of body like blood vessels, heart, etc. are affected.
Classification and Types of Neuropathy
Neuropathy can be classified into different categories based on the types of nerves or the location of the nerves that are affected or according to the disease that is causing it.
Broadly Neuropathy Can Be Categorized As Follows Depending On The Number Of Nerves Affected.
- Mononeuropathy – Single nerve is affected. Common examples are carpal tunnel syndrome, radial nerve palsy, ulnar nerve palsy as well as peroneal nerve palsy.
- Multiple Mononeuropathy – In this case, more than one nerve gets affected.
- Polyneuropathy – Term used when many peripheral nerves get involved. The most common examples are diabetic neuropathy and Guillain Barre syndrome.
As mentioned earlier, neuropathies are of different types based on the nerves that are affected.
Types of Neuropathy
Autonomic Neuropathy: In this condition the autonomic nerves are affected. Autonomic nerve damage has an impact on internal organs like heart, gastrointestinal and genitourinary system and involuntary functions are affected, which can lead to abnormal heart rate and blood pressure, reduced ability to perspire, bowel and bladder dysfunction, sexual dysfunction, and thinning of the skin.
Compressive Neuropathy: Also know as entrapment neuropathy, this refers to isolated peripheral nerve injury that occurs at definite locations where nerve gets constricted in a fibrous tunnel or gets deformed by fibrous band. The nerve can be injured by direct compression or stretching forces causing mechanical injury. Carpal tunnel syndrome and ulnar neuropathy at the cubital tunnel are the most common examples.
Hereditary Neuropathies: This is a group of inherited disorder affecting generally peripheral nervous system. Hereditary neuropathies can be categorized into four types: Hereditary sensory and autonomic neuropathy, hereditary sensorimotor neuropathy; hereditary sensory neuropathy as well as hereditary motor neuropathy. CMT disease, one of hereditary sensorimotor neuropathy, is most common type of neuropathy. Symptoms vary depending on type and may include symptoms like pain, numbness and tingling in extremities, weakness, and decreased muscle bulk, especially in lower legs and feet.
Diabetic Neuropathy: Diabetic neuropathy is the term used for damage to the nerves in the body that is done due to high blood sugar levels from diabetes. Often the symptoms develop slowly over the years and can vary depending upon the nerves that are affected. Symptoms may include heartburn, bloating, swallowing problems, nausea, constipation, or diarrhea.
Peripheral Neuropathy: The nerves of the peripheral nervous system i.e., the nervous system that is outside of the brain and the spinal cord, are damaged. This condition is called peripheral neuropathy, and most commonly the nerve axons are damaged. Peripheral neuropathy often causes numbness, pain, burning and tingling sensation in the arms, hands, legs and feet.
Pathophysiology of Neuropathy
Peripheral nervous system is the group of nerves that connect the central nervous system to the internal organs and muscles and transmit sensations throughout the entire body making sensation possible. The important clinical symptoms of peripheral neuropathy include pain, burning, numbness, tingling and aching of the distal limbs, as well as itching or extreme sensitivity to even the slight touch such as to a cloth or towel. These symptoms are generally bilateral and are more pronounced at night; and affect the legs more than the hands.
The pathological features of isolated neuropathies include a varying combination of focal demyelination and Wallerian degeneration.
Angulation and stretch injuries are main mechanisms of a nerve injury when there is ulnar neuropathy along with gross deformity of elbow joint as well as thoracic outlet disease. Continuous compression of nerves due to external forces also tends to cause focal nerve injuries like ulnar neuropathy at elbow and lesions in other branches of ulnar nerve in hand.
Causes and Risk Factors of Neuropathy
About 35% of neuropathies fall under idiopathic where cause of it is unknown. Diabetes is cause for another 35% of neuropathies and about half of people with diabetes develop some type of neuropathy. Rest of cases of neuropathies has various possible causes like:
- Pressure or trauma to nerves, most commonly from typing.
- Nutritional issues and vitamin deficiency.
- Autoimmune disorders like rheumatoid arthritis, lupus, Guillain Barre Syndromes.
- Tumors pressing on nerves.
- Infections and diseases like liver dysfunction, kidney dysfunction, Lyme disease, thyroid dysfunction etc.
- Inherited disorders.
- Exposure to toxins and certain drugs and cancer treatment.
There can be several risks for neuropathy. People suffering from diabetes who have poor control over their blood sugars are more prone to suffer from neuropathy. Individuals who have undergone organ transplantations, AIDS, or have immune suppression are at higher risk of developing neuropathy. Alcohol abuse or vitamin deficiency, particularly B vitamins, places at increased risk of neuropathy.
Signs and Symptoms of Neuropathy
Neuropathy symptoms depend on various factors, mainly the location of the affected nerves and the type of nerves that are affected i.e., sensory, motor, or autonomic. Some types of neuropathy may affect all the three types of nerves. Some of the neuropathies may arise suddenly while others develop gradually over a period of time, sometimes years. Some of the common symptoms are:
- Pins and needles in affected body parts. This can also be termed as tingling and prickling sensation.
- Burning sensation in the legs and feet and as the condition progresses it may also develop in the arms and hands.
- Stabbing, sharp pains which are more pronounced at night, sometimes described as electric-like pain, which starts from the legs and feet and progresses to the hands.
- Muscle weakness.
- Coordination problems.
- Increased susceptibility to skin infections and foot ulcers and other problems that affect the feet.
In autonomic neuropathy, patients may experience symptoms such as hypotension i.e., low blood pressure, where the patient may feel dizzy when getting up from sitting or lying position, accelerated heartbeat i.e., tachycardia, problems with balance, coordination problems, nausea, vomiting, dysphagia i.e., swallowing difficulties, diarrhea, bowel or bladder incontinence, problem emptying the bladder completely, impotence, erectile dysfunction, reduced ability to perspire, and thinning of the skin.
Diabetes is one of the most common causes of peripheral neuropathy though other causes can include infections, metabolic disorders, traumatic injuries, and exposure to toxins. Peripheral neuropathy often causes numbness, pain, burning and tingling sensation in the arms, hands, legs and feet. Symptoms can exist for any length of time, but they often improve with time, specifically in cases where there is an underlying condition that can be cured.
Peripheral neuropathy can eventually lead to dysesthesia where the patients' sense of touch is affected.
Motor nerve damage leads to symptoms that have an effect on the muscles such as cramps, spasms and muscle weakness. This type of neuropathy commonly leads to loss of balance and coordination. Patients may find difficulty with walking or running and feel heaviness in the legs, stumble frequently, or tire easily. Damage to nerves in the arms may make it difficult to do day to day activities like opening jars, turning door knobs and carrying bags.
Sensory nerve damage leads to symptoms such as impaired position sense, numbness, tingling, pinching and pain. Pain is often described as freezing, burning, or electric-like, and many patients report a sensation of wearing an invisible stocking or glove. These sensations are generally worse at night, and can become severely painful. Sensory nerve damage can eventually lead to lessening or absence of sensation, where nothing at all is felt.
Treatment for Neuropathy
There are a variety of treatments available for neuropathy that range from oral medications, creams to special diets and therapies that stimulate the nervous system. Antidepressants are a favored treatment for neuropathies as they relieve the neuropathic pain in people without depression. Anticonvulsants block calcium channels on neurons to limit pain and hence these are also frequently used in treatment. Narcotic and opioid treatments are also used to treat the condition, but are less favored because of risk of dependency, however, opioids have been consistently effective in reducing pain.
For some types of neuropathy, treatment with a topical anesthetic such as lidocaine is recommended. Capsaicin cream is also used to treat neuropathic pain.
Alternative therapies for peripheral neuropathy include Botox, cannabinoids, dietary supplements, chiropractic massages, meditation, yoga, cognitive therapy, and accupuncture.
Neuromodulators are also used in treatment of neuropathy. These include both implantable and non-implantable technologies such as implanted spinal pumps, spinal cord stimulators, electrodes that stimulate the motor cortex of the brain, and deep brain stimulators (DBS).
Investigations for Neuropathy
Peripheral neuropathy cannot be easily diagnosed in many cases. The standard diagnostic process begins with a full medical history and physical and neurological exams to analyze muscle strength and tone, tendon reflexes, examination of sensations, and posture and coordination. Other tests may include:
- Blood tests to measure the levels of vitamin B12, thyroid function tests, and urinalysis.
- Electromyography (EMG) and nerve conduction study (NCV).
- Nerve biopsy, where a small portion of nerve is removed and examined.
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