Skin disorders such as atopic dermatitis and psoriasis are extremely common and can be flared and develop further in any areas where people are scratching because of underlying itch related to neuropathic itch. Also frequently referred to as neurogenic itch, it’s a particularly demoralizing condition for a patient. These disorders compounding each other can be surprisingly debilitating. Symptoms can defy treatment. These disorders can significantly alter quality of life for patients, with burdens of disease similar to those noted among serious or life-threatening diseases such as cancer.
Neuropathic itch is a particularly vexing disorder. Diagnosis is difficult, sometimes taking several years. The itch is frequently unbearable, and treatment is often wholly inadequate. Itching can become distractingly severe, but traditional treatments usually fail to work. Intense scratching can damage the skin barrier, leading to injuries and infections that often interfere with diagnosis, and lead to hospitalizations. Diabetes is epidemic, and so is neuropathy secondary to diabetes. Pain and numbness are the usual problems, but many sufferers also experience itching.
Neurogenic itch: What it is
Neurogenic itch, largely known now as neuropathic itch, is an itching sensation that is caused by damage to neurons. It is not caused by eczema or allergy. The term neurogenic itch is often used in dermatology when the problem is localized to part of one extremity, or to one area on the back of elderly, less mobile individuals with dry skin.
Neuropathic itch is an itching sensation caused by neuronal damage.. It is a type of dysesthesia, or abnormal sensation. It usually occurs in one location. Itching can be severe, with scratching bringing only fleeting relief. Itch can occur along with other unusual sensations in the affected areas: these sensations can include wetness, pins-and-needles, burning, severe cold, numbness, and electric shocks. Itching might also be accompanied by a sense that the skin is “crawling.”
Occasionally, patients might experience heightened sensitivity in the skin affected by itch. Loss of sensitivity is also possible.
Causes of neurogenic itch typically have little to do with the skin, even though that is where the sensation is localized. This kind of itch is the result of a faulty relay of impulses between the peripheral nervous system, which involves the nerves that branch out from the spinal cord to the rest of the body, and the central nervous system (CNS), which consists of the brain and the spinal cord.
Neurons are special nerve cells that interpret impulses relayed by stimulation of nerve fibers.
Fibers called dendrites project from the neuron; they receive impulses relayed from other neurons by axons, another thread-like projection.
If any element of this infrastructure is damaged, sensory relay is impaired. Dysesthesias such as neurogenic itch are the result of this impairment.
Nervous system damage can originate through many different processes. In some cases, autoimmune disorders such as multiple sclerosis damage the neurons and/or the axons and dendrites. In others, injury to the brain and/or spinal cord causes neuronal death.
Infection can damage small nerve fibers, as often happens with infections of the varicella virus (chicken pox and shingles). Tumors can compress nerves or damage neurons. Medication can disrupt the relay of impulses or can cause neuronal death. Compression of the nerves by an injured or arthritic joint is another common source of neurogenic itch.
Potential sources of neurogenic itch:
- Vitamin deficiency
- Disc compression or impingement of nerve by inflamed joints
- Shingles infection
- spinal tumor
- Traumatic brain injury (TBI) or spinal cord injury (SCI)
- Exposure to toxins
- Trauma to the skin or underlying tissues
- brain tumor
- Autoimmune disorders, such as multiple sclerosis, lupus, Sjogren’s syndrome, or sarcoidosis
Diagnosis of neurogenic itch can be time consuming and involved. To rule out other conditions, doctors should take a highly detailed medical history. Patients should describe the itch in detail.
Discussing when the itch began and identifying potential origins is an important part of this history. Has the patient had shingles? Do they have a history of chemotherapy or radiation treatments? Are they experiencing any other dysesthesias, such as notalgia paresthetica? Notalgia paresthetica is a focal recurring itch highly associated with dry skin and
edema from dependency and lack of activity, i.e. sitting more and laying more.
Physicians will ask about conditions commonly associated with neurogenic itch, such as radiculopathy (caused by a pinched nerve), peripheral neuropathy, multiple sclerosis, or stroke.
The skin will be assessed, and doctors will ask if there have been changes since the itch began. The skin is usually normal at the onset of neuropathic itch; there are usually no signs of eczema or any other skin disorders. As the itch continues, however, scratching may damage the skin.
This can lead to the development of chronic prurigo nodularis, clusters of small, hard bumps. It can also cause thickening of the skin (lichen simplex). These are usually seen after long periods of neurogenic itch. While neurogenic itch is typically localized, it can spread more generally over time, either as a result of scratch-related damage or progression of the underlying cause of the symptoms.
The doctor may order a punch biopsy to measure intraepidermal nerve fiber density (IENFD), as the density of nerve fibers is usually reduced in patients with neurogenic itch or other dysesthesias. The doctor will be careful to avoid skin affected by eczema, scars, or infections, any of which might cause inaccurate findings. .
Bloodwork may be ordered to rule out itching caused by liver or kidney disease. A lumbar puncture (spinal tap) might be ordered if the doctor suspects multiple sclerosis. Radiologic imaging, such as CT scans and MRIs, are sometimes used to identify nerve compression caused by bone degeneration, injury, abscesses or tumors.
Neurophysiological studies such as nerve conduction studies and electromyography (EMG) are sometimes used to investigate how efficiently the nerves conduct impulses. In nerve conduction studies, electrodes are taped to the skin along a specific nerve pathway. A mild electrical shock is sent through the electrodes, which measure how fast the electrical current travels down the nerve.
The technician running the test will assess how rapidly muscles respond to electrical stimulation of motor nerves. They’ll likewise measure how long it takes one part of a sensory nerve to respond to stimulation elsewhere along the nerve.
During electromyography, needle-like electrodes are inserted through the skin into the muscle. The electrodes pick up electrical activity within the muscle, and it is displayed on a monitor called an oscilloscope that displays electrical activity in the form of waves. Electrical activity will be assessed when the muscle is at rest. The patient will then be asked to contract the muscles with varying degrees of force to assess electrical activity.
Where possible, treatment should involve management of underlying causes. This may involve surgery to correct a nerve compressed in the spine, or physical therapy to help with nerve impingement in the joints. Disorders such as MS should be managed with disease modifying therapies to prevent further damage of axons.
Subcutaneous injections of anesthetics may provide short-term relief for patients whose itch originates with damage to the superficial sensory nerves. Topical treatments such as steroid creams or antihistamine gels, which usually alleviate itching related to skin disorders, are ineffective against neurogenic itch. They can, however, provide relief of inflammation caused by scratching, which often exacerbates the itching.
Applying a low dose of topical capsaicin, the chemical that gives hot peppers their sting, may bring relief. Patients should keep in mind that the first applications tend to be painful and worsen the itch; this subsides, however, and subsequent applications often bring relief. Capsaicin must be applied four or five times daily, which may be difficult for many patients.
Oral medications are sometimes used for patients with severe neurogenic itch. The prescription depends upon the origin of the itching. Carbamazepine and oxcarbazepine are sodium channel blockers that calm irregular neuronal activity. Patients with brachioradial pruritus are commonly given gabapentin and pregabalin, which are also effective for treating neuropathic pain.
Patients should take steps to prevent scratching. If the urge is too great, wrapping the itching skin in a bandage or wearing gloves may be an option.
Dr. Harlan, a board-certified dermatologist, has his neurogenic itch patients apply a bag of frozen peas or ice covered with a thin, clean, cotton dish towel for two minutes. He recommends that they take Zyrtec at night and Claritin in the morning, when it is helpful for stabilizing histamine release from scratching.
For any redness, inflammation, or dermatitis either resulting from scratching or as a result of edema in an extremity, he advises using an extremely safe topical steroid cream such as SmartLotion® three or four times daily for two weeks. He then has them taper gradually to one application a day. Extra applications are allowed for intense itching spells.
SmartLotion® is a safe option for this regimen, because it uses a small amount of hydrocortisone (.75%) that will not cause skin atrophy or topical steroid withdrawal, even when used long-term, and it provides the benefit of a prebiotic strategy, when scratching has caused the microbiome to turn negative with potential pathogen overgrowth. These strategies also help prevent the complication of prurigo nodularis.
Dr. Harlan insists that his neurogenic itch patients moisturize regularly, using a product such as Perfect Repair™ that rejuvenates and protects the skin barrier, and helps to prevent inflammation.
In recent studies, cannabinoids have shown a lot of promise in treating neurogenic itch. In one study, neurogenic itch secondary to amyotrophic lateral sclerosis (ALS) responded extremely well to oral cannabinoids, with patients going from 7/10 on an itch rating scale to 3/10. Patients reported few effects, with no serious adverse effects. Cannabinoids represent a lot of potential for the treatment of neurogenic itch.
Treatment should consist of behavioral practices to minimize scratching, and may include systemic treatments such as carbamazepine (Tegretol®), Gabapentin, and pregabalin. Oral antihistamines such as Zyrtec and Claritin can lessen secondary itching triggered by scratching and underlying dermatitis.
Applying ice for five or ten minutes, and topical menthol and capsaicin products are useful for many. Safer low potency steroid creams such as SmartLotion® may relieve itching triggers secondary to scratching and underlying dermatitis conditions contributing to edema. Patients should be supervised with a skin check at least every 3 to 6 months. Patients should be very honest with their doctors about the severity of their symptoms. While neuropathic itch is difficult to treat, all avenues of relief should be pursued.
Steven Harlan MD
Board Certified Dermatologist
Inventor of SmartLotion®