Expert Insights On Painful Diabetic Neuropathy
Painful diabetic neuropathy is perhaps one of the most discussed and hotly debated subjects in podiatry. Emerging research and emerging treatments have fueled the fire even further. With this in mind, David G. Armstrong, DPM, a member of the American Diabetes Association’s National Board of Directors, posed a number of questions to leading authorities on this controversial subject. Here’s what they had to say … Q: How prevalent is painful diabetic neuropathy in your practice? A: All of the panelists note they see a large number of patients with neuropathy secondary to diabetes. At his facility, Barry Rosenblum, DPM, estimates that between 20 to 30 percent of these patients have some degree of pain related to their neuropathy. A. Lee Dellon, MD, says “all” diabetic patients who are referred to him have some degree of discomfort in their feet. Dr. Dellon says half of these patients describe their discomfort as numbness, buzzing, tightness or pressure whereas the other half of these patients use the word “pain” and also describe feeling a burning sensation. When he asks the patients who complain of pain if they have numbness as well, 80 percent of those patients say they do. When Dr. Dellon proceeds to evaluate these patients with neurosensory testing, he notes that all “have some loss of large fiber-mediated sensibility.” Out of 45,000 (mostly older male) patients seen at the Carl T. Hayden VA Medical Center, approximately 6,000 have been diagnosed with peripheral neuropathy, according to Jeffrey Page, DPM. Dr. Page says a third of the diabetes patients at the center have been diagnosed with peripheral neuropathy and approximately 15 percent of those patients are symptomatic. Andrew Boulton, MD, concurs with Dr. Page. While there’s a common misperception that the majority of patients with sensorimotor neuropathy have painful symptoms warranting treatment, Dr. Boulton says it’s more in the 10 to 15 percent range. He says it is much more common to see an insensitive foot at risk of ulceration and Dr. Boulton adds that a foot ulcer may be the first presentation of neuropathy. Dr. Boulton cites a number of studies. He points out that a 1993 study of over 6,000 diabetes patients in the United Kingdom revealed that the overall prevalence of neuropathy was 28 percent yet only a minority of these patients had significant symptoms.1 A population-based community study of foot ulceration among older patients with Type 2 diabetes in 1994 revealed that nearly half of the patients had significant sensory loss.2 Of these patients, less than half had significant symptoms, according to Dr. Boulton. Citing a more recent community-based study of nearly 10,000 diabetes patients, Dr. Boulton notes that approximately a fifth of the patients had significant neuropathic symptoms.3Q: What are the latest theories on the causes of painful diabetic neuropathy? A: Dr. Boulton and his colleagues have looked at the cause of this condition for many years and he says instability of blood glucose control is one of the most important causal factors. He adds that a recent paper in Diabetic Medicine showed that blood glucose flux is associated with neuropathic pain.4 According to Dr. Rosenblum, one of the latest theories on the cause of painful diabetic neuropathy centers on the possibility of an entrapment mechanism. He says this would substantiate the “double-crush phenomenon,” as espoused by Dr. Dellon. Dr. Dellon says patients with painful neuropathy have a unique histopathology. To document this condition, Dr. Dellon says you need measured cutaneous thermal thresholds, a sural nerve biopsy demonstrating a shift in nerve fiber diameter histogram and normal large fiber function (normal cutaneous pressure and vibratory thresholds). The most common tests for diagnosing neuropathy (e.g. nerve conduction velocity) are only capable of recognizing large fiber disease, according to Dr. Page. However, he notes that when these tests are positive, the disease is already “well-advanced.” What has become better understood in recent years is the fact that diabetic neuropathy is “initially and foremost a small fiber neurological disease,” maintains Dr. Page.5 He says newer objective studies allow earlier detection of changes in the smaller myelinated and non-myelinated nerve fibers (e.g.