A-Delta Pain Fiber Nerve Conduction Study Benefits Patients With Spinal Pain
Because spinal pain has many causes, any test that can accurately diagnose the source of pain serves as an invaluable tool for making sure the patient receives the correct treatment. A 2002 study by Cork et al studied the nerve conduction of pain fibers with a device that had 94.6% sensitivity in detecting lumbar nerve-root function pathology as confirmed by epidurograms.1 The basis for this type of testing is the pain fiber nerve conduction study (pfNCS). The pfNCS uses electrical voltage applied at predetermined points that correspond to areas innervated by a specific nerve root2 to determine whether that nerve root has a normal response to the current. A hyperresponse indicates increased sensitivity to the current, while a hyporesponse indicates impaired sensitivity of that nerve root.
Despite the sensitivity of the pfNCS, no prospective clinical studies have been able to demonstrate that the pfNCS improves the management and clinical outcomes of patients with spinal pain any better than other methods. Indeed, the Center for Medicare and Medicaid Services in 2004 concluded that prototype devices (like that used by Cork), which relied on the patient’s psychophysiological assessment (perception of a sensation), were unacceptable for Medicare coverage because, “there continues to be insufficient scientific and clinical evidence to consider the pfNCS test and device used in performing this test as reasonable and necessary.”3
More recently, however, the use of a potentiometer, in conjunction with pfNCS, precisely recorded an objective increase of 20 millivolts or more a second or two before the patient felt a sensation generated by the pfNCS.4 Thus, theoretically, the pfNCS gives more than just a “psychophysiologic assessment” as to whether a given patient perceives pain.
This study was undertaken to determine the effectiveness of the pfNCS in improving outcomes of patients suffering from cervical and lumbar pain. The pfNCS (performed with a Neural-Scan, PainDX, Inc., Laguna Beach, California) employs a voltage-regulated stimulus in conjunction with a potentiometer, an objective measurement of the amplitude of the action potential.
Evaluating the sensitivity of the test in determining which nerve generates a given patient’s pain, as well as the specificity of that test in reducing the patient’s pain while improving the patient’s function, will demonstrate whether the use of the pfNCS is “reasonable and necessary.”
From August 1, 2008, through July 31, 2009, 151 individual pfNCS electrodiagnostic examinations were performed on 124 patients, who were then followed for at least 1 month after receiving treatment. The patients’ ages, sexes, clinical diagnoses as determined by history, physical findings, x-rays/magnetic resonance imaging/computed tomography scans, and results of the pfNCS were recorded. The pfNCS results demonstrated that a given nerve root had one of six responses: a normal, mild, moderate, marked, severe, or very severe reaction (see box). All patients had their visual analog scale (VAS) and Oswestry Disability Index (ODI) measured and recorded before and after they received treatment. Patient treatment was dependent upon what the pfNCS showed to be causing the patient’s pain.
If the results were normal, the patient underwent conservative treatments including physical therapy, medication, and counseling where indicated. If the results showed mild, moderate, or marked nerve root abnormalities, then diagnostic medial branch facet joint blocks (MBB) were performed at the appropriate level according to International Spine Intervention Society Guidelines,5,6 and medial branch facet rhizotomies were performed when indicated.7,8 If the results showed severe or very severe nerve root abnormalities, then transforaminal lumbar epidural steroid injections (TF/LESI), LESI, or cervical epidural steroid injections (CESI) were performed at the appropriate level. Some patients received other interventional techniques such as sacroiliac (S/I) joint injections, piriformis injections, percutaneous disc decompression (Disc Dekompressors, Stryker, Kalamazoo, Michigan), or vertebroplasties.
The test results were then divided into three categories (Table 1). The treatment selected for a given patient was considered to have “helped” if the patient’s VAS was reduced by at least 2 points or 25% and/or the ODI was less than 40 and improved by at least 25%.9 Overall average changes in the VAS and ODI were evaluated using several different parameters. In addition, the patients were divided into those who had pfNCS of either the lumbar or cervical spinal regions and evaluated according to the treatment given to them and their response to treatment.
Data from 151 pfNCS were analyzed. The average patient age was 56.9 years, with a range of 14 to 94 years; 59 men and 92 women were tested. Of the patients tested, the average decrease in VAS score was 49% and an average functional improvement in the ODI was 44%. When analyzed by category, results of the pfNCS had one of three influences on the treatment patients received: change in the treatment given (56%, n=84); confirmation of what clinical findings recommended as appropriate treatment (35%, n=53); no influence on treatment (9%, n=14).
Of those 84 patients where the pfNCS helped change treatment, 72 tests (86%) helped patients decrease their VAS scores by 75%, on average, and demonstrated approximately 42% improvement in functioning. Of special note are the 12 patients where the pfNCS changed the side that received treatment (8%). None of these 12 patients would have had the correct side of their pain generator treated without the use of the pfNCS. On average, these 12 patients demonstrated an 88% decrease in their VAS and a 54% improvement in function.
As noted, the pfNCS also confirmed what the patient history, physical findings, and diagnostic tests such as plain x-ray films, CT scans, and MRIs suggested should be the appropriate treatment. Of these 53 patients, improvement was seen in 40 patients (75%), while 13 patients (25%) were not helped. The average patient in this group decreased their VAS by 55% and improved their ODI by 55%.
Fourteen of the pfNCS did not influence the treatment a given patient received; 6 patients (43%) were helped anyway and 8 patients (57%) were not helped. On average, those treated in this group had a 42% decrease in VAS and a 27% improvement in ODI.