- How to Diagnose Diabetic Peripheral Neuropathy
- Literature review of the usefulness of nerve conduction studies and electromyography for the evaluation of patients with carpal tunnel syndrome. AAEM Quality Assurance Committee.
- Causes of Polyneuropathy
- ADA 63rd Scientific Session: Abstract 830-P. Presented June 14, 2003
How to Diagnose Diabetic Peripheral Neuropathy
Diabetic peripheral neuropathy (DPN) is a "diagnosis of exclusion." Diagnostic challenges are one thing but few practitioners relish that phrase when it comes to DPN.
For this condition, the practitioner needs to cast a very wide net of tests and keep an open mind regarding clinical suspicion in order to reach an accurate diagnostic conclusion. How likely is it that there could be another neuropathy-causing disease or medical condition resulting in these same lower extremity symptoms? Does the podiatric physician really need to consider thyroid problems, vitamin B12 deficiencies, nerve entrapments, lupus, kidney failure, nutritional deficiencies and alcoholism among other diagnoses?
Noted Mayo Clinic researcher Peter J. Dyck, MD, strongly cautions that the physician diagnosing DPN must first eliminate the presence of other neuropathy-inducing conditions because there is an estimated 10 percent occurrence of other neurologic diagnoses in patients who have concurrent diabetes. To fail to diagnose and treat these other conditions (or make an appropriate referral to other physicians) could be catastrophic for the patient’s outcome.1
That said, it is neither an easy nor inexpensive task to eliminate that 10 percent of outlying cases. The potential list of comparisons is a long one with vague symptoms. Indeed, when you treat patients with diabetes, you likely hear these common comments:
- "My feet burn."
- "I feel electric shocks in my toes."
- "My toes are numb at the end of the day."
- "I can’t get to sleep at night because my feet feel like they are on fire."
Many of the treatments are not benign. Surgery has the inherent risks associated with anesthesia and potential postoperative complications of infection and scarring. Medical (pharmaceutical) treatments can have adverse effects and drug interactions. Given the fact that there is no completely benign treatment, there is a profound desire to make a definitive diagnosis prior to embarking on a treatment plan. This brings us back to the pivotal question: How does one distinguish between diabetic peripheral neuropathy and the array of other causes of these same symptoms?
What The International Consensus Group Recommended
While it might seem like there is a circuitous trip in reaching a diagnosis, there is usually a very distinct roadmap leading to the correct diagnosis. At least there is if one agrees with the International Consensus Group, which arose out of suggestions made by Neurodiab, a subgroup of the larger European Association for the Study of Diabetes. The internationally respected members, primarily Europeans, debated and discussed the subject for several years before agreeing on criteria required for a correct diagnosis of DPN.5
The panel of 39 experts from the European countries and Canada also had four representatives from the United States, including Lawrence B. Harkless, DPM, of the University of Texas Health Science Center at San Antonio and Aristidis Veves, MD, of the Beth Israel Deaconess Medical Center and Harvard Medical School. This panel of diabetologists, podiatrists, neurologists, diabetes specialists, nurses and primary care physicians advocated an annual assessment in order to facilitate early diagnosis of neuropathy. Once one has diagnosed the condition, the panel said it is essential to manage it aggressively and/or make appropriate referrals within the multidisciplinary team in order to minimize complications of the condition.
The international and multidisciplinary panel was mindful of the limitations of available modalities that might exist in different countries. Accordingly, the panel wanted to develop an easy to follow system that would enable the podiatrist in America to have the ability to reach the same conclusion as the diabetologist in Finland. With that in mind, the International Consensus Group concentrated on developing guidelines that did not require any technologically advanced or expensive equipment to make the diagnosis.5
In regard to the panel’s recommendations for clinicians, it emphasized gathering a comprehensive history of the patient’s symptoms, his or her type of diabetes, the patient’s lifestyle and social circumstances. For the lower extremity exam, the panel recommended a subjective analysis by the examiner that assessed the health status of the skin (i.e., absence of sweating, presence of ulcerations and callosities), immobility of joints, gait and footwear.
The panel recommended that clinicians perform simple tests to assess peripheral sensation. These tests include sensation to pinprick, light touch, vibration (utilizing a 128-Hz tuning fork), pressure and ankle reflexes.
Pointing Out The Flaws Of Simple Tests And Subjective Patient Responses
The International Consensus Group recommended simple and easily available tests for diagnosing DPN but are these tests accurate? Dr. Dyck, a Professor of Neurology at the Mayo Clinic College of Medicine, and others disagree with the group’s findings, citing the system for "major flaws."1
Dyck points out the shortcomings of the pinprick/tuning fork regimen, noting there are more sensitive and reliable modalities available, such as the biothesiometer or the vibrometer. (However, these modalities are not universally available in all practice settings and this was a requirement of the consensus group.) Dyck also expressed concern about the variability of examiners’ judgment about anthropometric factors of age, gender, height and weight.
In order to make the diagnosis of DPN, Dyck cites the presence of at least two abnormalities from the broad group of neuropathy symptoms, clinical abnormalities and emphasizes the use of nerve conduction, quantitative sensation tests (QST) or quantitative autonomic tests (QAT). This noted neurologist specifies that one of the abnormal findings must be abnormal nerve conduction in at least two separate nerves or an abnormal QAT.1
Dyck’s gold standard is a composite score he calls the "Neuropathy Impairment Score (Lower Limbs) + 7 Tests" (NIS). The NIS is an evaluation of muscle weakness, a decrease or loss of reflexes and a loss of sensation. There are also scores for the patient’s age, gender, physical fitness and anthropometric features. The "seven tests" are peroneal motor nerve conduction, velocity, peroneal compound muscle action potential, peroneal motor distal latency, sural sensory nerve action potential and tibial motor distal latency, heart-pulse rate decrease with breathing and vibratory detection threshold.1
The comprehensive system also includes algorithms for determining a quantifiable score. This quantifiable score leaves little question as to the diagnosis of DPN. However, for what this system offers in specificity, it is an impossibly difficult system for the private practitioner to utilize and would seem better suited for the specialist or researcher who needs the detail for comparison studies.
A Lack Of Reproducible, Objective Techniques
Yet Dyck has a point as the more commonly used examinations (pinprick, reflexes, tuning fork) result in almost entirely subjective findings.1 In addition, the results are often not reproducible, even when these techniques are performed by the same examiner.
There is also the uncertainty of the response by the patient. For a variety of reasons, whether it is an attempt to please, a fear of disease or an inability to understand what is being asked, patients may respond incorrectly either knowingly or unknowingly.
Are these variables the responsibility of the examiner, the patient or the testing modality? The answer is an unsatisfying "yes" to all. Unfortunately, the very nature of peripheral neuropathy is that it is a condition that is transient, intermittent and variable in its presentation.6
Nothing short of nerve biopsies (or if one subscribes to the reliability of EMG/NCV for diagnosis of DPN) are independent of a declaration by the patient.
It is probably not surprising that DPN is often diagnosed when complications occur. Indeed, many of the most severe outcomes occur in the feet. At that point, the condition has progressed to Stage 3 with lesions and possibly subsequent amputations.5
Finding A Diagnostic Combination That Works
The recommended physical examination includes a comprehensive dermatologic exam including evaluation of dyshidrosis, callosities, ulcerations and other abnormalities. One should also note any deformed or limited joints, abnormal gait and evaluate the type of footwear worn by the patient.
One can augment patient history and the physician exam with available diagnostic testing (objective) such as the Peripheral Specified Sensory Device (PSSD, Sensory Management), EMG/NCV and others.4-6
PSSD. The PSSD, invented by A. Lee Dellon, MD, a Professor of Plastic Surgery and Neurosurgery at the Johns Hopkins University School of Medicine, is capable of detecting nerve damage earlier than other modalities including nerve conduction velocity examinations.8
This early, pain-free diagnostic test allows earlier intervention and possible reversal of the condition through treatments like surgical neurolysis (release of specific peripheral nerves) because it picks up degeneration of neural tissue before it is completely irreversible.
EMG/NCV. Nerve conduction velocity studies record the speed at which impulses travel through nerves and measure electrical responses in a quantifiable fashion. Although the two tests are usually referred to as the EMG/NCV, one would usually order the NCV first and follow it with the EMG if necessary. It records electrical activity in muscles and allows one to differentiate between muscle disease and neurological disease.
Semmes-Weinstein. Semmes-Weinstein monofilaments (SWM) are inexpensive testing devices, which are manufactured of calibrated nylon monofilaments that can generate a reproducible bending stress. The higher the number of the monofilament, the more force it will require to bend. The most commonly used device is the 5.07, which requires 10 g of force to buckle the monofilament.
The aforementioned differential diagnosis for peripheral neuropathy includes those medical conditions that cause symmetrical loss of sensation in the extremities. These conditions include thyroid abnormalities, anemia, vitamin B12 deficiency, alcoholism, nutritional deficiencies, lupus and multiple other conditions.
To rule out these medical conditions, one must order the appropriate tests for each if you suspect their presence. On occasion, the patient may require a nerve or muscle biopsy, electroencephalography, lumbar puncture and advanced imaging modalities such as MRI and CT scans in order to determine the etiology of a difficult to diagnose neuropathy.
Ensuring a quick, accurate diagnosis of neuropathy can limit nerve damage and preserve the patient’s function and sensation.
Dr. Satterfield is an Clinical Associate Professor at the University of Texas Health Science Center at San Antonio.
- Gries FA, Cameron NE, Low PA, Ziegler D. Textbook of Diabetic Neuropathy. Thieme Medical Publishers, 2003.
- Kochman AB, Carnegie DH, Burke TJ. Symptomatic reversal of peripheral neuropathy in patients with diabetes. J Am Podiatr Med Assoc. 2002 Mar; 92(3):125-30.
- Sindrup SH, Jensen TS. Efficacy of pharmacological treatments of neuropathic pain: an update and effect related to mechanism of drug action. Pain. 1999 Dec: 83(3):389-400.
- Valdivia JM, Dellon AL, Weinand ME, Maloney CT Jr. Surgical treatment of peripheral neuropathy: outcomes from 100 consecutive decompressions.J Am Podiatr Med Assoc. 2005 Sep-Oct;95(5):451-4.
- Boulton AJM, Gries FA, Jervell J. Guidelines for the Diagnosis and Outpatient Management of Diabetic Peripheral Neuropathy. Diab Med 15:508-14, 1998.
- Rathur HM, Boulton AJ. Recent advances in the diagnosis and management of diabetic neuropathy. J Bone Joint Surg Br. 2005 Dec; 87(12):1605-10.
- Feldman EL, Stevens MJ. Clinical testing in diabetic peripheral neuropathy. Can J Neurol Sci 1994. Nov; 21(4):S3-7.
- Wood WA, Wood MA, Werter SA, Menn JJ, Hamilton SA, Jacoby R, Dellon AL. Testing for loss of protective sensation in patients with foot ulceration: a cross-sectional study. J Am Podiatr Med Assoc. 2005 Sep-Oct;95(5):469-74.
- Bild DE, Selby JV, Sinnock P, et. al. Lower-extremity amputation in people with diabetes: epidemiology and prevention. Diabetes Care. 1989;12:24-31.
- Birke JA, Sims DS. Plantar sensory threshold in the Hansen's disease ulcerative foot. Read at the Proceedings of the International Conference on Biomechanics and Clinical Kinesiology of Hand and Foot; Madras, India; December 16-18, 1985.
- Kamei N, Yamane K, Nakanishi S, et al. Effectiveness of Semmes-Weinstein monofilament examination for diabetic peripheral neuropathy screening. J Diabetes Complications. 2005 Jan-Feb; 19(1):47-53.
- Kumar S, Fernando DJS, Veves A, et. al. Semmes-Weinstein monofilaments: a simple, effective and inexpensive screening device for identifying diabetic patients at risk of foot ulceration. Diabetes Res Clin Pract. 1995;13:63-68.
- Olmos PR, Cataland S, O’Dorisio TM, et. al. The Semmes-Weinstein monofilament as a potential predictor of foot ulceration in patients with noninsulin-dependent diabetes. Am J Med Sci. 1995;309:76-82.
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Literature review of the usefulness of nerve conduction studies and electromyography for the evaluation of patients with carpal tunnel syndrome. AAEM Quality Assurance Committee.Department of Neurosciences, University of California San Diego.
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Causes of Polyneuropathy
|Endocrine / Metabolic||
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ADA 63rd Scientific Session: Abstract 830-P. Presented June 14, 2003
ADA 63rd Scientific Session: Abstract 830-P. Presented June 14, 2003.
In the analysis of nearly 7,500 patients, both primary care physicians and endocrinologists failed to diagnose non-severe neuropathy in about two thirds of cases, reported a team led by William H. Herman, MD, MPH, professor of internal medicine at the University of Michigan at Ann Arbor. When it comes to severe neuropathy, about one in four endocrinologists and one in three primary care physicians miss the boat, the study suggested.
"Many patients with diabetes have evidence of peripheral neuropathy that is not being picked up as early as it should be," said co-investigator Laurence Kennedy, MD, FRCP, professor of medicine and chair of the Division of Endocrinology at the University of Florida in Gainesville. This is troubling because without early diagnosis and prompt treatment, patients with peripheral neuropathy are at increased risk for foot ulcers and even amputation, said ADA President Eugene Barrett, MD, PhD. Dr. Barrett, professor of internal medicine at the University of Virginia in Charlottesville, echoed the researchers' call for routine testing for neuropathy on a regular basis.
"Peripheral neuropathy is one of the most troubling complications of diabetes," he said. "It's an area where we all, primary care doctors and specialists alike, can do a better job."
If a diabetic patient comes in complaining of pain, diagnosis is a snap, he said. "But when the nerves aren't functioning and the patient is numb and doesn't complain, it's easily missed."
Dr. Barrett's straightforward prescription: "Do a foot exam on all diabetic patients when they come in for their annual exam. If there is loss of sensation, you probably have your diagnosis."
For their report, the researchers analyzed data from the ongoing GOAL A1C study, the objective of which is to assess the impact of point-of-care testing in a large population of patients predominantly treated in a primary care setting. As part of the evaluations, patients are screened for the presence of neuropathy using monofilament testing.
ElectroDiagnostics Studies Assess Function, Not Structure
EDX testing – ElectroDiagnostic studies assess function not structure.
Any readily accessible nerve can be tested.
- Motor nerve conduction studies examine the motor unit, which includes the nerve cell body in the spinal cord, the nerve axon, the neuromuscular junction, and the muscle fibers innervated by the nerve.
- Sensory nerve conduction studies test large-diameter nerve fibers that carry information and vibrations from receptors in the skin to the cell bodies in the dorsal root ganglion (proximal to the spinal cord)
Recording - the electrodes record the electrical signal.
Differential amplifier - Amplifies the signal received from the electrodes (by 1000) and subtracts the background noise.
Oscilloscope - translates the electrical signal into an action potential wave that is read on the screen.
Demyelination – loss of the myelin sheath insulating the nerves. When myelin degrades, conduction of signals along the nerve can be impaired or lost, resulting in slower conduction of nerve signals.
Axonal loss - shows direct damage to the nerve and is typical in diseases that affect the nerve cell such as diabetes and alcoholism.
- Calculated by precisely measuring the distance (millimeters) between the stimulation and the recording and dividing the distance by the time (milliseconds).
- A nerve signal should travel at around 150 km / hour. Below a certain level (around 100 km/hour) is considered abnormal.
Low velocity = demyelination!
Amplitude - measures the total axonal response to the electrical stimulation. If the wave form shows reduced amplitude then the axonal response to the electrical stimulation is affected. Axonal loss is caused by toxic damage to the nerves.
Low amplitude = axonal loss!
Common Errors in NCS
- Incorrect measurement - the most common source of error in NCS is. In entrapment neuropathies especially a difference of a few mm is critical to the result.
- Temperature - cold temperature can slow conduction and increase latencies so it is important to keep the patients limbs warm.
- Incorrect stimulation - at both the elbow and the knee, errors are often made by indirectly stimulating an adjacent nerve.
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