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Correlation of Electrodiagnostic and Clinical Findings in Unilateral S1 Radiculopathy

Lumbosacral radiculopathy is a challenging diagnosis, and Electrodiagnostic study (EDX) is a good complementary test for Magnetic Resonance Imaging (MRI). Physical examination, MRI and electrodiagnosis have different diagnostic values in this regard. MRI can provide anatomical evidence and is useful in choosing a treatment process, but it could also have false positive results. In this study, we assessed the correlation of clinical and electrodiagnostic findings in patients with positive MRI findings for S1 radiculopathy. EDX was performed for 87 patients referred with clinical and MRI diagnosis of S1 radiculopathy. The consistency between EDX results, MRI, and clinical findings were evaluated by Pearson chi 2 and odds ratio. Fifty-eight percent of patients had disc protrusion, and 42% had extrusion. Physical examination revealed absent Achilles reflex in 83% and decreased S1 dermatome sensation in 65%. In this study, EDX sensitivity was about 92%. The highest consistency among EDX parameters and physical examination findings was between absent Hreflex and decreased Achilles reflex (OR=6.20, P=0.014), but there was no significant consistency between Hreflex and neither muscular weakness nor SLR test result (P>0.05). There was also no relationship between type of disc herniation in MRI and H reflex. There was correlation between H-reflex abnormalities and absent ankle reflex in patients with unilateral L5-S1 disc herniation in MRI. Results of this study showed that in patients with positive MRI for L5-S1 disc protrusion and S1 nerve root compression, it is still beneficial to perform EDX for selected patients. © 2019 Tehran University of Medical Sciences. All rights reserved. Acta Med Iran 2019;57(4):229-234.


Introduction
Lumbosacral discopathy is one of the most common causes of low back pain. Estimated lifetime prevalence of lumbosacral radiculopathy is about 3-5 % of the general population (1). The intervertebral disc between fifth lumbar and first sacral vertebrae (L5-S1) is the most susceptible point to herniation accounting for 42% of all lumbar disc herniation (2). Lumbosacral radiculopathy is a challenging diagnosis. EDX is a useful way to help diagnosis because the test is very specific and is, therefore, a good complement to lumbosacral MRI, which is a very sensitive, but not specific test. In addition, it is the unique test to evaluate the physiologic function of the spinal nerves to see if they are damaged or not. A comprehensive study can also help excluding differential diagnoses that cause pain or neurologic changes in the lower extremity as well as a rule in the diagnosis of radiculopathy. In the hands of a skilled examiner, EDX is very specific and can help us to rule out some differential diagnoses that are very common (3). In some studies, two limb muscles plus associated lumbar paraspinal muscle abnormality, two limb muscles abnormality, or one limb muscle plus associated lumbar paraspinal muscle abnormality in EMG had 97%, 96%, and 92% specificity, respectively for radiculopathy (4). The specificity of 0.85% was reported for EDX in another study (5). There are other studies that showed EDX couldn`t be replaced by MRI (6), but there is not any systematic review regarding this comparison. Therefore as lumbosacral radiculopathy has no golden standard test, in both research and the clinic, a combination of history, physical examination, imaging, and EDX are used to confirm the diagnosis (3).
There are multiple clinical, imaging, and electrodiagnostic tests to detect S1 radiculopathy (2,7). As we know lumbar radiculopathy has various presentations. Some patients are vague historians, and physical exam is neither high sensitive nor specific in these patients. Because of this and because there is no gold standard test for diagnosis it is common for patients to undergo further testing. From an evidence-based medicine perspective, it can be difficult to assess the value of these tests (3).
Imaging (especially MRI) can well depict disc degeneration and herniation. However, there is very poor consistency between imaging findings of disc herniation and the clinical presentation or course. In another word, MRI is more sensitive than clinical findings and consequentially has a large amount of false positive (8). For example, lumbar disc protrusions can be seen as high as 67% of asymptomatic patients older than age 60, and more than 20% have lumbar central stenosis (3).
Electro-diagnostic studies including electromyography and nerve conduction study, when performed by an expert physician is a very valuable method to diagnose root involvement. It is especially valuable in patients whose physical examination is not reliable (7) and also in highly suspicious patients who have negative MRI, so we suspect to non-compressive radiculopathy such as infective or immune-mediated. EDX is very helpful in the workup of patients who have multiple level involvements and also in patients who are at the risk of neuropathy (3). One study found that needle EMG is very specific in the diagnosis of lumbar radiculopathy when the appropriate EDX criteria are used (92 % specificity). Electrodiagnostic study for radiculopathy has low number of false positive result (6).
Among EDX findings, H waves are very helpful in the diagnosis of S1 radiculopathy. In some studies, it has been mentioned to be definite sign of S1 radiculopathy even without the need to accomplish needle electromyography (9)(10)(11)(12). This wave has several strengths, including the ability to detect injury to sensory fibers and they are not dependent on a window of opportunity to discover abnormalities as is the needle examination, because they become abnormal as soon as compression occurs and the deficit can last indefinitely (12). The aim of the present study was to describe the utility of electro-diagnostic studies in confirming clinically suspected diagnosis and investigate the consistency between clinical and para-clinical findings (EDX) in a high suspected patient of S1 radiculopathy with positive MRI result.

Materials and Methods
This study was conducted prospectively in Shohadae-Tajrish Hospital of Shahid Beheshti University in 2016 in Tehran, Iran. Our patients were referred from neurosurgery department with a high clinically suspicion of S1 radiculopathy and positive results of MRI through 3 weeks ago. All 87 patients referred between 2014 Oct and 2016 April which their diagnosis was suspicious or needed more evaluation to make better decision for treatment were included in this study consecutively. None of our patients had local soft tissue infection or other contraindication to do EDX. All patients who were included in this study signed informed consent. The inclusion criteria were: 1. Low-back pain radicular to one lower limb 2. The onset of symptoms between 3 weeks to 3 months ago.
Individuals with bilateral radicular symptoms, previous spine surgeries, polyneuropathies, focal neuropathies in the lower limb, myopathies and known motor neuron diseases were excluded from the study.
In physical examination, the ankle reflex, SLR (straight leg raise) test, plantar flexion strength and sensory loss in S1 territory were examined. Manual muscle testing was recorded in the grading system of the Medical Research Council Scale; full available Range of Motion (ROM) is achieved against gravity and is able to demonstrate maximal resistance (5/5). Full available ROM is achieved against gravity and is able to demonstrate moderate resistance (4/5). Full available ROM is achieved against gravity but is not able to demonstrate resistance (3/5). Full available ROM is achieved only with gravity eliminated (2/5). A visible or palpable contraction is noted, with no joint movement (1/5). No contraction is identified (0/5) (14). Achilles reflex was determined by taping Achilles tendon with a reflex hammer in the prone position and assessed as 0 (no response), 1+ (diminished but present and might require facilitation), 2+ (usual response), 3+ (more brisk than usual), 4+ (hyperactive with clonus).
We performed EDX studies to confirm the diagnosis and also to determine the severity or progressive axonal loss.

Para clinic evaluation
Electrodiagnostic (EDX) test was performed by a two-channel synergy electro-diagnostic instrument (Medelec™ Synergy T-EP). Needle EMG with a concentric needle electrode was performed by an experienced physiatrist who was full professor of physical and rehabilitation medicine.

Nerve conduction studies (NCS)
Standard EDX techniques (13) were used for sural, saphenous and superficial peroneal nerves' sensory conduction studies. Sensory Action Potentials (SNAPs) and Nerve Conduction Velocities (NCVs) of above nerves were calculated. Surface electrodes were used for NCS.
Motor conduction studies were also performed for tibial and deep peroneal nerves, and Compound Motor Nerve Action Potentials (CMAPs) were recorded from Abductor Hallucis and Extensor Digitorum Brevis muscles. Nerve Conduction Velocities (NCVs) of both tibial and deep peroneal nerves were also measured.
Patients with impaired nerve conduction studies including patients with peripheral nerve injury, lumbosacral plexopathy or polyneuropathy were excluded from the study.
Also patients with history of radiation, immune or infectious diseases which could induce post irradiational radiculitis, plexopathy, infective or immune-mediated radiculopathy were excluded.
H-reflex was recorded from gastro-soleus muscle using Braddom's technique by submaximal stimulation over the tibial nerve (14). We also adjusted these values for patients' leg length and age. All these electrodiagnostic tests were done in both limbs.

Statistical methods
Statistical analysis was conducted using SPSS version 20. Association between EDX parameters and clinical findings were calculated by odds ratios with observed level of significance determined by Pearson chi2 test. Also paired T-test was used to assess changes in continuous variables. P<0.05 was considered as the significance level.

Results
During this 18-month-study, 87 patients with high suspicion of clinical and imaging findings for unilateral S1 radiculopathy were referred to our EDX lab. Demographic and clinical characteristics of the patients are shown in table 1.  Electromyography showed neurogenic pattern (neurogenic MUAPs or active denervation) in 92% of subjects. Only 7 patients were normal on EMG exam, and 80 patients had positive findings as showed in Table-3 (Total Sensitivity=92%). The highest sensitivity was for active denervation (37.9%) and then chronic neurogenic pattern (27.6%) ( Table 3). There was no correlation between the type of disc herniation in MRI and type of EMG abnormalities in the electro-diagnostic study (P=0.13).

Discussion
Low back pain with radiating pain to the lower limb is the most common reason for the reference to EDX lab. EDX has been used to assess for lumbosacral radiculopathy diagnosis, determine the involved roots, physiologic function of nerve and severity of the lesion. They also can serve as extensions of the clinical history and physical examination, and confirm neuro-imaging result (15). In our study, EMG and H-reflex sensitivities in diagnosing lumbosacral radiculopathy were 92% and 87%, respectively and the two most common physical examinations were decreased Achilles reflex and S1 dermatome abnormality. In another investigation, sensory loss in the painful dermatome was the most frequent finding at physical examination (56% of cases), and EMG was abnormal in at least one myotome in 42% of cases (16).
Recently there are some evidence about the role of EDX before surgery to know which patients have better prognosis, but this is beyond the scope of this article. Hreflex is routinely used to evaluate S1 radiculopathy diagnosis. The H-reflex diagnostic criteria are latency difference between two sides, prolonged latency, and absence of H-reflex (12)(13). The diagnostic sensitivity and specificity varies widely in studies. The sensitivity and specificity of 50% and 91% are reported for H reflex, respectively (8). In the present study, ankle jerk reflex abnormalities were followed by H-reflex latency abnormality in 91% of patients. In similar investigations, H-reflex study was abnormal in 88% of subjects (17). Bobinac reported that EMG abnormalities indicating S1 radiculopathy were followed by H or F wave latencies abnormality in 63% of patients. The rest of patients (37%) showed mild EMG abnormalities followed by normal H or F wave (11). Our study revealed similar results: there was significant association between EMG findings and H reflex (P=0.066). Normal EMG finding was followed by normal H or F wave in 64% of patients. In a study performed by Katirji, the maximal H-reflex amplitude and the maximal H/maximal M amplitudes associated in a positive slope with the ankle jerk (18). In most of the previous studies, H-reflex abnormalities including Hreflex latency or its absence were strongly associated with ankle reflex.
In a study conducted by Lauder to determine the extent to which the history and physical examination predict the outcome of the electro-diagnostic (EDX) evaluation in patients with suspected lumbosacral radiculopathy, the history, and physical examination couldn't reliably predict the electro-diagnostic outcome (2). But there was a strong association between the presence of an abnormality in the respective reflex and radiculopathy at that level. For example, subjects with an abnormal Achilles reflex were more than eight times more likely to have S1 radiculopathy than those with a normal Achilles reflex (19). These findings are almost consistent with the results of our study.
Finally, we should say imaging can be considered complementary to electro-diagnostic medicine. It depicts disc degeneration and disc herniation and also can suggest the presence of discogenic abnormality, but the lack of a gold standard obviates any definitive conclusions. As we know, there is very poor correlation between imaging findings of disc herniation and the clinical presentation or course (9). In our study, EDX findings were applied for confirming the diagnosis of disc herniation, but there was no significant correlation between the pattern of disc herniation (extrusion vs. protrusion) and electro-diagnostic results including EMG findings, H-reflex latency, etc.
In conclusion, in the population of patients with suspected lumbosacral radiculopathy referred for an EDX study, generally physical examination may not be reliable at predicting EDX outcome. However, ankle reflex can be assessed and considered as H-reflex study in electrodiagnostic testing. This study also showed that in a patient with positive MRI findings for S1 radiculopathy, at the presence of an expert EMG man, it is still beneficial to perform EDX study in particular for patients who are candidate for surgery intervention or those with negative MRI results. However, MRI and EDX are complementary to each other. MRI investigates the anatomical change of discovertebral complex, and electrodiagnostic studies provide physiologic information. EDX could reveal nerve root compression its progress, its stage: being acute or chronic lesion, but imaging and other investigations may be necessary to determine the exact cause of spinal nerve damage other than disc herniation.