Neurological Itches and Why Scratching Doesn't Help

Not all itches are the same. A neurological itch, also known as a neuropathic itch, is a type of itch caused by nerve damage rather than issues related to the skin. The itch tends to be chronic (persistent) and often difficult to treat.

This article explores how neurological itching differs from other types of itching as well as the symptoms, causes, and treatment options.

What Is an Itch?

As common as itches are, they are often hard to define from a scientific standpoint. Pruritus, the medical term for itchiness, can be described as an unpleasant sensation that causes the urge to scratch.

The part that is harder to describe are the processes that trigger an itch. Though there are many possible causes of an itch—including dry skin, allergies, infections, drug reactions, autoimmune diseases, liver or kidney disease, and cancer—the actual mechanisms that lead to an itch are similar.

There are two basic ways itching happens:

• Neural pathway activation: This is when nerve endings are activated and send signals to the spinal cord and brain that are translated into a physical sensation. For an itch to occur, more than one type of nerve fiber—mostly so-called A-and C-fibers—needs to be activated. The activation of other combinations of fibers can lead to pain, numbness, and other sensations.
• Chemical mediators: These are chemicals in the body that activate nerve fibers. There are many different types of chemicals that can do this, including histamine and cytokines. Different conditions can trigger the release of these chemicals, from allergies to infections and diseases.
  

Types of Itch

There is not just one type of itch. Itches differ not only in their causes but also in which part of the nervous system they originate. This includes the central nervous system (made up of the brain and spinal cord) and the peripheral nervous system (involving nerves outside of the brain and spinal cord),

There are four basic types of itches:

• Pruriceptive itch: This is an itch that starts in peripheral nerves in the skin. It can be caused by an allergic reaction, inflammation, skin dryness, or other skin damage.
• Psychogenic itch: This is a type of itch usually linked to mental illnesses, such as delirium.
• Neurogenic itch: This is a type of chronic itch that originates in the central nervous system and is caused by organ diseases like kidney failure or cirrhosis.
• Neurological (neuropathic) itch: This is another type of chronic itch caused by nerve damage. This can involve either the central nervous system or the peripheral nervous system.
  

Symptoms

Neuropathic itching differs from other types of itching in that it can often happen along with neuropathic pain. This is because the disorders that cause neuropathic itching affect the same nerve pathways that cause neuropathic pain.

Neuropathic itching is often described as prickly, burning, or crawling and may be accompanied by numbness, coldness, electric-like shocks, or sensations of wetness. There may also be increased or decreased skin sensitivity.

And unlike some other types of itching, scratching can actually make neuropathic itching worse.

Causes

There are many things that can cause neuropathic itching. The itching may be a result of the neuropathic pain disorder (such as with post-herpetic neuralgia caused by shingles) or it may be the primary or sole symptom.

Some of the common causes of neuropathic itching are:

• Trigeminal trophic syndrome: This is a condition caused by the misfiring of the trigeminal nerve that relays signals from the face to the brain. Chronic itching is a main symptom. 
• Brachioradial pruritis: This is a type of chronic itch that usually affects the arms and may be related to sun exposure. 
• Notalgia paresthetica: This is a sensory disorder that usually affects the left side of the body just below the shoulder blade. A traumatic injury or spinal nerve impingement (a.k.a. pinched nerve) is often involved.
• Spinal cord lesions: Different types of lesions, including neurofibromas (a type of tumor) and cavernous hemangiomas (an abnormal cluster of blood vessels) can cause chronic itching on unrelated parts of the body.
• Brain lesions: Stroke, multiple sclerosis, and other conditions that cause brain damage are also known to cause chronic itching on other parts of the body.

Treatment

Neuropathic itching is difficult to treat. Typical anti-itch remedies like antihistamines or topical steroids are usually of little to no help. Some conditions like trigeminal trophic syndrome don't respond well to treatment, such that people may need to wear protective gloves to avoid injuring themselves by scratching.

Doctors will often first recommend conservative therapies before moving on to more complex treatments if those don't help. Treatment options include:

• Ice application, which is especially helpful with brachioradial pruritus
• Topical capsaicin, a pepper-based cream applied to the skin
• Topical lidocaine, a type of anesthetic applied to the skin
• Antiseizure drugs like gabapentin and Lyrica (pregabalin)
• Thalidomide, a drug used to treat certain cancers
• Botox injections, used to dull nerve signals
• Nerve blocks, used to temporarily block nerve signals
• Neurostimulation, electrical or magnetic devices that help treat nerve dysfunction
• Mind-body therapies to reduce your psychological response to itching

Summary

A neurological itch (a.k.a. neuropathic itch) is caused by injury to nerve fibers in the brain, spinal cord, skin, or other parts of the body. Unlike many other types of itch, neuropathic itches often involve nerve pain and often get more intense the more you scratch.

The causes of neuropathic itching are many and often difficult to treat. Treatment options range from ice application and over-the-counter creams to more complex therapies, like anti-seizure drugs and Botox injections.