Neuropathic itch, also known as neurogenic pruritus, refers to chronic itching caused by damage to the somatosensory nervous system. It can be severely debilitating and significantly impact a person’s quality of life. Testing for neuropathic itch involves taking a thorough medical history, conducting a physical exam, and ordering diagnostic tests to help determine the underlying cause. Early diagnosis and treatment are essential to provide relief and prevent complications.
What causes neuropathic itch?
Neuropathic itch has a wide range of potential underlying causes, including:
– Nerve damage or dysfunction from trauma, surgery, infection, autoimmune disorders, tumors, or metabolic conditions
– Spinal cord injuries
– Multiple sclerosis
– Postherpetic neuralgia (nerve pain after shingles)
– Brachioradial pruritus (itching on the outer arm caused by nerve compression)
– Notalgia paresthetica (itching in the back caused by spinal nerve impingement)
Anything that damages or compresses the somatosensory nerves can potentially lead to neuropathic itch. The itch is typically confined to the region innervated by the affected nerves.
Key symptoms
Some of the hallmark symptoms of neuropathic itch include:
– Intense, unrelenting itching, often with no rash or skin changes
– Itching, tingling, prickling, or burning sensations
– Itching attacks that come and go
– Worsening of symptoms in response to touch, pressure, or temperature changes
– Itching that interferes with sleep and daily activities
– Scratching provides no relief or even worsens itching
– Skin damage, lesions, and scarring from chronic scratching
Medical history
Taking a detailed medical history is the first step in evaluating potential neuropathic itch. The doctor will ask about:
– Location, severity, duration and triggers of itching
– Any related symptoms like pain or numbness
– Past nerve damage, trauma, or neurological conditions
– Current medications and supplements
– Family history of neurological or autoimmune disorders
Information obtained from the medical history can help narrow down the differential diagnosis and guide subsequent testing.
Physical examination
Next, a physician will conduct a thorough physical exam. This involves assessing:
– The appearance of the affected skin for signs of lesions, scarring, or changes in texture
– Distribution of itching and any accompanying sensory changes
– Presence of rashes, hives, or skin inflammation
– Signs of underlying neurological disease, such as impaired reflexes, sensation, or muscle weakness
– Evidence of nerve root compression, spinal cord injuries, or brain lesions
– Enlarged liver and spleen that may indicate lymphoma
The physical exam provides important clinical clues to help determine potential causes of neuropathic itch.
Diagnostic tests
Based on the medical history and physical exam, doctors may order tests to aid diagnosis, including:
Blood tests
– Complete blood count to check for infection or hematologic disorders
– Liver and kidney function tests to assess organ health
– Thyroid tests, fasting glucose, and vitamin levels to uncover metabolic abnormalities
– Serum protein electrophoresis to detect monoclonal gammopathies
– Erythrocyte sedimentation rate and C-reactive protein to identify inflammation
– Antinuclear antibodies, rheumatoid factor, and complement levels to evaluate for autoimmune diseases
Imaging studies
– X-rays to check for fractures, lung cancer, or other structural abnormalities
– CT scan of the head to look for brain tumors or lesions
– MRI of the spine to detect nerve compression or spinal cord diseases
– PET scan to map abnormal metabolic areas suggesting metastasis or lymphoma
Nerve conduction studies
– Can measure how well and how fast electricity moves through peripheral nerves
– Help locate areas of nerve damage in conditions like peripheral neuropathy
Skin biopsy
– Takes a small sample of skin to examine under a microscope
– Helps identify nerve fiber abnormalities and diagnostic markers of certain skin disorders
Other more specialized tests like lumbar puncture or nerve biopsy may sometimes be warranted based on clinical suspicion.
How do doctors diagnose neuropathic itch?
There is no single confirmatory test for neuropathic itch. Doctors make the diagnosis by:
– Identifying characteristic symptoms of chronic, refractory itching without primary skin changes
– Excluding other potential causes like dermatologic, systemic, or psychogenic conditions
– Detecting signs of neurological dysfunction through exam findings, diagnostic testing, and patient history
– Locating corresponding areas of neurological pathology that could be causing neuropathic itch
– Assessing response to treatment trials of medications used for neuropathic pain/itching
The most common diagnostic approach involves a combination of thorough history and physical exam, imaging studies, blood tests, and sometimes skin biopsy or nerve conduction studies.
What conditions cause neuropathic itch?
Some key examples of underlying disorders that can produce neuropathic itch include:
– Diabetes mellitus – Diabetic neuropathy affects nerves and can cause neuropathic itch, especially in lower extremities
– Postherpetic neuralgia – Nerve pain and itching after shingles, caused by damage from the varicella zoster virus
– Brachioradial pruritus – Cervical spine pathology irritates the brachioradial nerves causing outer arm itching
– Notalgia paresthetica – Degeneration of thoracic spinal nerves produces itching in the mid-back
– Multiple sclerosis – Demyelination of central nerves can lead to itch and other sensory disturbances
– Nerve compression or trauma – Physical irritation of peripheral nerves from trauma, tumors, radiotherapy, or surgery
– Paraneoplastic itch – Immune reactions triggered by cancer, such as lymphoma, indirectly cause nerve damage and itching
The underlying problem causing the neuropathic itch will dictate the appropriate treatment approach.
Are there risk factors for neuropathic itch?
There are several risk factors that may predispose individuals to developing neuropathic itch, including:
– Prior herpes zoster infection (shingles)
– Diabetes, especially with poor glycemic control
– Autoimmune diseases like multiple sclerosis
– History of physical nerve trauma from accidents, surgery, or radiation therapy
– Cervical or thoracic spinal pathology like disk herniation or spondylosis
– Advanced age
– Cancer
– HIV/AIDS
– Kidney disease
– Alcoholism
– Nutritional deficiencies of vitamin B12, folate, or iron
Neuropathic itch can also occur without any identifiable cause. Having one or more risk factors prompts closer monitoring and evaluation if itch develops.
How is neuropathic itch treated?
Treatment focuses on addressing the underlying condition causing neuropathic itch, providing symptomatic relief, and preventing complications of chronic scratching. Key aspects of treatment include:
– Topical anesthetics like lidocaine to temporarily numb itchy areas
– Oral antihistamines to reduce itching and scratching urges
– Capsaicin creams to desensitize nerves
– Topical corticosteroids to decrease inflammation
– Antidepressants like doxepin that have anti-itch properties
– Anti-seizure medications like gabapentin to calm abnormal nerve activity
– Opioids for severe refractory neuropathic itch unresponsive to other therapies
– Phototherapy using controlled UVB exposure is sometimes beneficial
– Psychotherapy including coping techniques if there is a psychogenic component
Identifying and addressing the root pathological process is key to controlling symptoms long-term. Severe refractory cases may require experimental treatments like neuromodulatory devices. Multimodal therapy combining medications, topicals, and non-pharmacological approaches often provides the best results.
What is the prognosis for neuropathic itch?
The prognosis depends on the specific causative disorder:
– Itching from diabetes, shingles, or trauma may gradually improve over 6-12 months as nerves regenerate
– Chronic conditions like MS or spinal cord disorders result in recurrent episodes of itching
– Malignancy-related itch carries a grave prognosis without treating the cancer
– Unidentified causes may produce lifelong itch
– Secondary infections and skin damage from scratching can cause further complications
While bothersome and impairing when active, neuropathic itch is rarely fatal. Patient education on preventative scratching techniques is vital. Some cases of neuropathic itch spontaneously resolve but it can become a chronic problem requiring long-term management.
Conclusion
Neuropathic itch arises from disease processes damaging the somatosensory nervous system. A systematic diagnostic approach is needed to uncover the underlying etiology. Testing includes a medical history, physical exam, imaging studies, and lab work to pinpoint the source of nerve irritation. Treatment centers on treating the primary pathology when possible, alongside medications and modalities to alleviate itch symptoms. While prognosis depends on the cause, multidisciplinary management can significantly improve quality of life for neuropathic itch patients.
