Neurostimulation: Can It Have An Impact For Painful Diabetic Neuropathy?
While current modalities for the symptoms of painful diabetic neuropathy include oral medications, topical therapies and surgical treatment, emerging research suggests the potential benefits of neurostimulation. Accordingly, these authors review the current literature and offer insights on proper patient selection for appropriate referrals.
Peripheral neuropathy is a common long-term complication of diabetes. Approximately 7.5 percent of unselected adults attending a hospital diabetes clinic have painful neuropathic symptoms, mostly in the lower extremities.1 Patients suffering from diabetic neuropathy report sensory complaints of numbness, tingling and pain as well as weakened motor function. This alteration in motor function can progress into changes in biomechanics as well as deformities of the foot and, subsequently, ulceration.
The sensory symptoms occur in a “stocking and glove” distribution. Patients with diabetic neuropathy also experience a loss of sudomotor function in the extremities with additional complaints of thick dry skin associated with the autonomic system.2 This painful neuropathy can have a major impact on the quality of life of these patients and also poses a significant financial burden. It can be associated with substantial costs from utilization of healthcare services, work loss and disability.3 Additionally, nighttime exacerbation of the pain and contact hypersensitivity to clothing and bedding may result in loss of sleep. This in itself can be disabling and frustrating.4
The exact pathophysiology of chronic sensory motor diabetic neuropathy is not completely understood. However, metabolic as well as microvascular systems appear to be involved.4 Patients with diabetes often suffer from angiopathy with the impaired microcirculation affecting the function of peripheral nerves.
Dellon described two metabolic changes that occur in the peripheral nerves of patients with diabetes.2 The first is increased water content within the nerve as a result of glucose being metabolized into sorbitol. This increased volume makes the nerve more susceptible to chronic compression, especially in areas of anatomic narrowing such as the tarsal tunnel. The second metabolic change is a decrease in the slow anterograde component of axoplasmic flow, which transports the lipoproteins necessary to maintain and rebuild the nerve. Increased external pressure increases the intraneural pressure. This subsequently decreases blood flow and results in an ischemic condition for the peripheral nerve.
Current Treatments For Painful Diabetic Neuropathy
Conventional treatment for painful peripheral diabetic neuropathy is largely symptomatic and often ineffective with undesirable side effects.4 A starting point in the management of patients with diabetic neuropathy should include an evaluation of their glycemic control.2 To monitor this, one may use laboratory tests such as blood glucose levels and glycohemoglobin (hemoglobin A1c).
Physicians have used a variety of pharmacological agents in the treatment of neuropathic symptoms. Dellon reports the classic triad of neuropathic medications to include carbamazepine (Tegretol®, Novartis), phenytoin (Dilantin®, Pfizer) and amitriptyline (Elavil®). Many patients are unable to tolerate the side effects of carbamazepine and phenytoin is often not effective. A common side effect of amitriptyline is drowsiness. Many patients with neuropathy suffer from difficulty sleeping, which makes this side effect of amitriptyline a desirable one.2
Duloxetine (Cymbalta®, Eli Lilly), gabapentin (Neurontin®, Pfizer), pregabalin (Lyrica®, Pfizer) and Metanx® (Pamlab) are additional modalities physicians may employ to help treat symptoms of neuropathy. Many patients do not tolerate the doses required of non-narcotic neuropathic pain medication or simply cannot accept the decrease in cognitive function these drugs induce.2 One may employ topical agents such as capsaicin cream and lidocaine patches for localized pain.
Podiatrists may consider surgical treatment such as a tarsal tunnel release in patients with a diagnosed entrapment neuropathy.