Fighting Neuropathic Pain — Stem Cell Research Points to New Treatments for a Debilitating Condition
By Mark D. Coggins, PharmD, BCGP, FASCP
Today’s Geriatric Medicine
Vol. 13 No. 2 P. 14
Neuropathic pain (NP) is a common and difficult-to-treat symptom of nerve damage. Patients suffering from this chronic pain condition are at risk of incurring increased health care expenditures and experiencing significant reductions in quality of life. Patients with NP often report job loss or significant changes to their careers, limited social interactions, decreased quality time with family, and feelings of hopelessness and depression due to their disease.1 Furthermore, current treatment approaches for NP, which focus on symptom management, are frequently inadequate.
Advancements in stem cell research are promising and may lead to new treatment modalities for NP.
NP Symptoms
NP symptoms are frequently described as burning, electric, tingling, and shooting. Hallmarks of NP include allodynia (pain resulting from a stimulus that normally does not elicit a painful response) and hyperalgesia (greater pain than normally would be expected from a painful stimulus).
Symptoms of neuropathy range from mild to disabling and may include a loss of reflexes, problems feeling pain, changes in temperature, numbness and tingling, and pain that is often worse at night.2 Symptoms are often sudden and unpredictable and follow different patterns that vary over a period of days, weeks, or years.1,2
Causes/Types
Approximately 30% of cases of neuropathy are the result of diabetes, and about 60% to 70% of people with diabetes have mild to severe forms of damage to sensory, motor, and autonomic nerves that cause such symptoms as numb, tingling, or burning feet; one-sided bands of pain; and numbness and weakness on the trunk or pelvis.2
More than 100 types of neuropathy have been identified, each with its own characteristic set of symptoms and prognosis.2 Causes of NP include chronic medical conditions (eg, diabetes), physical injury (eg, fractures, spinal cord injury), alcoholism, amputation (resulting in phantom pain), use of some chemotherapeutic agents (eg, Cisplatin, Vincristine), radiation therapy, trigeminal neuralgia, infections (eg, shingles, HIV), central nervous system disorders (eg, Parkinson’s disease, multiple sclerosis), kidney and liver disorders, nutritional deficiencies and imbalances (eg, B12 deficiency, excess B6), autoimmune disorders (eg, Guillain-Barré syndrome, rheumatoid arthritis, lupus), and some cancers/tumors. In some cases, NP is idiopathic.1-3
Available Treatments
Existing treatments and approaches to NP focus on palliative management of symptoms. There are no drugs available that can restore nerve function. The management of NP is challenging, as this type of pain is frequently refractory to existing treatments.4 It’s been reported that in clinical trials, no more than one-half of patients with NP experience clinically meaningful pain relief.3 Similarly, several studies of individuals with NP living in the community have shown patients on average experience pain of moderate severity despite taking prescribed medications for their pain.4
Medications commonly used include analgesics such as opioids (eg morphine, methadone, tramadol) and over-the-counter pain medications (eg, NSAIDs), antidepressants (eg, amitriptyline, nortriptyline, venlafaxine, duloxetine), anticonvulsants (eg, gabapentin, pregabalin), muscle relaxers (eg, cyclobenzaprine), and topical agents such as lidocaine creams or patches. In addition to medications, nondrug therapies and lifestyle modifications such as exercise, physical therapy, acupuncture, and limiting physical activity may also be utilized to manage symptoms.
Stem Cells
Stem cell transplantation has the potential to repair, restore, replace, and regenerate cells, and may be able to treat a number of different medical conditions and diseases. Research increasingly is evaluating the use of stem cells for the treatment of NP. Unlike existing treatments that focus only on symptom management, stem cell transplantation may be able to replace damaged nerve cells, possibly offering a cure.
Stem cells, sometimes referred to as “master cells,” are the foundation for every organ and tissue in the human body. These include embryonic stem cells and tissue-specific adult stem cells. Due to the ethical issues associated with the use of embryonic stem cells, most of the research being done involves the use of adult stem cells. Regardless of the type used, stem cells have the unique ability to self-renew (make copies of themselves) and differentiate (develop into more specialized cells).
Stem cells can be transplanted in a number of different ways, including local delivery, intrathecal or intracerebroventricular administration, IV injection, intranasal delivery, and endogenous mobilization by drugs for chronic intractable pain treatment.
In early research, it had been thought that stem cells would need to be administered intrathecally to reduce pain as IV administration appeared to result in the stem cells becoming trapped in the lungs, preventing their migration to the site of injury. However, more recent evidence suggests this lung trapping effect may be transient.
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