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By Louise M. Klebanoff, MD
Associate Professor of Clinical Neurology, Weill Cornell Medical College
Dr. Klebanoff reports no financial relationships relevant to this field of study.
Synopsis: Using the clinical history and simple, inexpensive laboratory tests, community-based outpatient neurologists were able to determine the cause of distal symmetric polyneuropathy in three-fourths of patients presenting with typical symptoms. More costly diagnostic testing, including electrophysiological testing and magnetic resonance imaging, did not add to the accuracy of diagnosis or management of this patient population.
Source: Callaghan BC, et al. Role of neurologists and diagnostic tests of the management of distal symmetric polyneuropathy. JAMA Neurol 2014:71:1143-1149.
Peripheral neuropathy is the most common disorder of the peripheral nervous system, with a prevalence of 2-7% in the entire population and a prevalence of > 10% in the elderly. Disorders of the peripheral nervous system account for 1.5 million visits to neurologists annually. Diagnostic testing of these disorders by outpatient neurologists can be costly. The cost for diagnostic testing is $375 million each year, $205 million (57%) for electrodiagnostic tests and $135 million (38%) for magnetic resonance imaging (MRI). For distal symmetric polyneuropathy (DSP), the most common subtype of peripheral neuropathy, current evidence supports several routine and inexpensive diagnostic laboratory studies including fasting glucose, vitamin B12 level, serum protein electrophoresis, and glucose tolerance tests for the initial evaluation. Few data are available to assess the value of more expensive diagnostic testing such as electrophysiological testing and MRI in the assessment of patients with DSP. In addition, the value of the community neurologist in the diagnostic testing and management of patients with DSP is unknown.
The authors performed a retrospective cohort study using a validated case-capture method to identify all patients with a new diagnosis of DSP treated by community neurologists is Nueces County, Texas, from April 1, 2010 through March 31, 2011. Patients were required to meet the Toronto Diabetic Neuropathy Expert Group consensus panel definition of probable neuropathy, which is two or more of the following criteria: neuropathic symptoms (self-report of pain, numbness, and/or tingling in the feet and/or legs), decreased distal sensation on neurological examination, or decreased or absent ankle jerks. Patients who were seen only in the hospital, who only underwent electrophysiological testing, or who were previously diagnosed as having neuropathy by a neurologist were excluded. Medical records were extracted by a trained research coordinator using the entire outpatient medical record. The suspected causes of the neuropathy, as identified by the neurologist at the initial evaluation and at the last follow-up evaluation, were also documented. All management changes were also recorded.
The authors screened the medical records of 4890 patients, identified 831 by the initial screening criteria, and excluded 86 due the previously defined exclusionary criteria and another 287 who did not meet the Toronto consensus for probably DSP, leaving 458 patients for further analysis. The mean (SD) age of the patients was 65.8 (12.9) years, and 258 (56.3%) were women. The mean duration of follow-up was 435.3 (44.1) days over 2.4 (1.6) visits. Neurologists ordered electrodiagnostic testing in 353 patients (77.1%) and MRI of the neuroaxis in 65 (14.2%). In terms of the Academy of Neurology recommended tests, measurement of vitamin B12 level was ordered in 177 patients (38.6%), fasting blood glucose in 56 (12.2%), serum protein electrophoresis in 127 patients (27.7%), and glucose tolerance tests in 144 patients (31.4%).
Prior to diagnostic testing, neurologists were able to determine the cause of DSP in 291 patients (63.5%), with the most common cause being diabetes (233 patients) followed by thyroid condition (31 patients), alcohol (14 patients), chemotherapy (9 patients), and vitamin B 12 deficiency (8 patients). Before diagnostic testing, 167 patients (36.5%) had no clearly defined cause for their DSP; with diagnostic testing a new cause was determined in 45 patients. In total, neurologists discovered a new cause of DSP in 71 patients, 28 with prediabetes, 20 with vitamin B12 deficiency, eight with diabetes, and eight with thyroid disorders. Neurologists determined a new cause for DSP in eight patients based on history alone (toxic medications, alcohol, inherited neuropathy, peripheral vascular disease, poliomyelitis, and steel-toed shoes) and determined another four cases based on history and/or laboratory abnormalities (renal disease, hypoglycemia, and the metabolic syndrome). Two patients were no longer considered to have DSP after diagnostic testing.
Management changes were either introduced or suggested in 289 patients (63.1%), most commonly altering medications (262 patients). A total of 224 patients (48.9%) had a change in their neuropathic pain medications, with most of these changes involving a GABAergic agent such as gabapentin or pregabalin (145 patients), a tricyclic antidepressant (53 patients), or a serotonin-norepinephrine reuptake inhibitor (49 patients). Potential disease-modifying management change was made in 113 patients (24.7%), including improved diabetes management (45 patients), vitamin treatment (39 patients, 33 with vitamin B12), encouraging diet and exercise (33 patients), changing thyroid medication (10 patients), recommending alcohol cessation (eight patients), and discontinuation of medications thought to be neurotoxic (four patients). Two patients were treated with corticosteroid medication, one with a known mixed connective tissue disease and another with newly diagnosed Sjogren syndrome.
Electrodiagnostic studies, ordered in 353 patients, led to a change in identified cause and/or management in only two patients; in both cases, the change in cause was from a neuropathy diagnosis to a non-neuropathy diagnosis. Neuroaxis MRI, ordered in 65 patients, did not lead to a change in management in any case. The diagnostic testing that most frequently led to management changes included testing for diabetes, thyroid studies, and measurement of vitamin B12 levels.
With a detailed clinical history and several simple and inexpensive laboratory screening studies, community-based neurologists could identify the cause of DSP in nearly 75% of patients presenting for outpatient evaluation. Diagnostic evaluation led to clear diagnosis in 10% of patients with a previously undetermined cause of DSP. The most common new diagnoses were diabetes, prediabetes, thyroid disease, and vitamin B12 deficiency. The use of more expensive electrodiagnostic testing and MRI rarely added to the diagnosis or management of this patient population. Neurologists commonly made management changes, including pain management and treatment of the underlying cause of DSP. Neurologists recommended changes in pain medication for almost half of the patients with DSP, emphasizing the importance of the neurologist in the management of this patient population. The vast majority of these changes involved the three classes of neuropathic pain medication with the best level of evidence to support their use, with rare use of nonsteroidal anti-inflammatory drugs or narcotics.
In this retrospective cohort study of 458 patients with symptoms of DSP presenting to outpatient community neurologists, neurologists were found to make clinically important contributions to the diagnosis and management of this patient population. Relying on clinical history and several inexpensive diagnostic laboratory studies, the etiology of the DSP could be determined in nearly three-quarters of this patient population. In the majority of patients, neurologists contributed to the management of both the underlying cause of the DSP as well as evidence-based pain management. The use of costly diagnostic studies, such as electrophysiological testing and MRI of the neuroaxis, was not found to increase the diagnostic yield or change patient management. It is recommended that electrophysiological testing be reserved for patients with atypical presentations such as concern for inherited, vasculitic, or demyelinating neuropathy and that MRI of the neuroaxis be reserved for those in whom spinal stenosis is a clinical concern. Compliance with the recommendations of the American Academy of Neurology to screen for diabetes, vitamin B12 deficiency, and para-proteinemia in patients presenting with DSP is reinforced; the data presented in the study suggest that thyroid functions should also be tested routinely.