Timed Vibration Sense and Joint Position Sense Testing in the Diagnosis of Distal Sensory Polyneuropathy

INTRODUCTION

Distal sensory polyneuropathy (DSP) is a disease of the peripheral nerves and has a prevalence of 2.1%–8% in the general population.[1] Diabetes mellitus, impaired glucose tolerance, alcohol use, B12 deficiency, paraproteinemia, inherited conditions, and drugs contribute to form the more common causes of DSP.[2] DSP commonly presents with distal symmetric sensory symptoms and rarely with imbalance while walking.[3] Patients with DSP that predominantly affects the large sensory fibers (A-beta somatic fibers), present with tingling paresthesias and have impairment of joint position sense (JPS) and vibration sense (VBS) with absent ankle jerks.[4] On electrophysiological testing, the sensory nerve action potentials (SNAPs) are reduced or absent. Patients with DSP restricted to small nerve fibers (A-delta fibers and unmyelinated C fibers), have minimal findings on the neurological examination, such as reduced pinprick or temperature sensation, preserved ankle jerks, and normal nerve conduction studies.[5] Despite advances in the available technology, neurological examination continues to play an important and pertinent role in the evaluation of patients with neurological illness. However, there are limited data on its utility, and hence, there is a need for more research in this field.[6] Several studies have explored the role of the neurological examination in DSP, but these were mostly restricted to specific subgroups of patients such as diabetic polyneuropathy.[78] Very few studies have explored the correlation between symptoms, examination findings, and electrophysiological results.[7910] Timed VBS and JPS are integral parts of the sensory clinical examination, but there are limited data on its diagnostic utility.[101112] Hence, the objective in this study was to study the utility of joint position and timed VBS testing in the diagnosis of DSP.

METHODS

This was a prospective study conducted in the neuroscience department of a tertiary care hospital in India. The study was approved by the Institutional Review Board and Ethics Committee. Between the periods of August 2017 and December 2017, consecutive patients who presented to the electrophysiology laboratory of the neuroscience department with a clinical diagnosis of a DSP were screened, and those patients who were between 18 and 80 years of age and electrophysiological studies confirmed DSP were included in the patient group. Patients with acute neurological disorders, joint pathologies, disorders affecting consciousness, or awareness making them unable to cooperate for the examination and patients with skin lesions were excluded from the study. Normal participants who were willing to undergo nerve conduction studies and patients with nonneurological conditions and a normal nerve conduction study were included as the control group. The principal investigators who performed the tests for the study were blinded to the allotment of the groups. Participants of both the groups underwent timed VBS and JPS testing.

RESULTS

A total number of 321 participants (189: male, 132: female) were recruited to the study. A total of 127 participants had DSP as evidenced by symptoms, neurological examination, and electrophysiological evaluation (abnormal lower limb SNAPs). One hundred and ninety-four participants without any neurological deficits and normal SNAPs were taken as controls. Among patients with DSP, abnormal clinical examination was found in 95%. The abnormal findings on the baseline neurological examination included impaired sensation over the feet 66%, impaired ankle jerk (70%), impaired VBS (85%), and impaired JPS (39.6%).

The normative data of the VBS testing from the controls are given in Table 1. Joint position testing done in the controls had the number of mean correct values as 9.5 out of 10 trials with a standard deviation of 1.2. One of the normal participants aged 65 years had absent JPS at the great toe. None of the normal participants had absence of the VBS at the great toe. The clinical and electrophysiological characteristics of the patients with DSP and the normal controls are given in Table 2. Diabetes mellitus was the most common (38.6%) etiology for DSP. The diagnostic accuracy of timed VBS and JPS testing is given in Table 3. The receiver operating characteristic curves for the diagnosis of DSP using timed VBS and JPS testing at the great toe is given in Figure 1. The area under the curve for JPS and VBS testing at great toes was 0.63 and 0.73, respectively. The optimal cutoff value for VBS testing at the great toe to make a diagnosis of DSP was a response lasting <8 s. At this cutoff value, the sensitivity was 85% and specificity was 42.8%. The optimal cutoff point for JPS testing at the great toe was 2 or more incorrect responses. At this cutoff, the sensitivity was 33% and specificity was 87.6%.

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Figure 1

Receiver operator characteristic curves for the diagnosis of distal sensory polyneuropathy using joint position sense and vibration sense testing at the great toe. Receiver operating characteristic curves for the diagnosis of distal sensory polyneuropathy using vibration sense and joint position sense at the great toe. The area under the curve for joint position sense and vibration sense at the great toes is 0.63 and 0.73, respectively. The optimal cutoff value for vibration sense testing at the great toe to make the diagnosis of distal sensory polyneuropathy was a response lasting <8 s. At this cutoff value, the sensitivity was 85% and specificity was 42.8%. The optimal cutoff point for joint position sense testing at the great toe was 2 or more incorrect responses. At this cutoff, the sensitivity was 33% and specificity was 87.6%

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DISCUSSION

Our study shows a high sensitivity for VBS testing and a high specificity for joint position testing in the diagnosis of DSP. The etiology of DSP in our patient group was varied with diabetes mellitus being the most common cause. The role of sensory examination has already been studied in diabetics with DSP and found to be useful.[789] The second most common etiology for DSP was cryptogenic/idiopathic DSP. Previous studies on DSP have shown a similar proportion of cryptogenic DSP.[121] Hence, our study results could be applied to DSP of varied etiology, especially diabetes mellitus and cryptogenic DSP. In a study similar to ours, Abraham et al. have found a higher sensitivity and specificity for neurological examination in the diagnosis of DSP.[12] The differences in the results could be related to the differences in study setting, severity of DSP, and methods of testing. Our study was prospective, examiners were blinded to the clinical history and electrophysiological data, and also, only large fiber sensations were tested. However, the study by Abraham et al. was a retrospective study where the examiners were not blinded to the patient's clinical history, reason for referral, and suspected diagnosis. Overestimation of neurological signs is known in this setting and could be a possible contributing factor.[7] JPS testing at the great toe has been used for assessing the proprioceptive pathways.[14] Detection of movements at the interphalangeal joint of the great toe is known to be markedly worse than that of other joints, and a minimum displacement of at least 20° is needed to perceive the direction of movement.[22] Furthermore, as DSP affects the longest nerves of the lower limbs first, testing at the great toes for JPS is ideal for testing for DSP. In our study, JPS was found to be highly specific (87.6%) when there were 2 or more errors in a trial of 10. Hence, JPS can be used to rule in the diagnosis of DSP when further testing is not possible. Bedside tuning fork tests, using a 128-Hz tuning fork for assessing VBS can be qualitative or quantitative. In one method of qualitative testing, complete loss of the vibration sensation is categorized as abnormal. Other qualitative methods of testing include comparing the patient's perception with that of the examiner. This is done by placing the examiner's finger on the opposite surface of the joint being tested from the tuning fork, and noting if the vibration persists after the patient no longer senses it, or assessing the patient's threshold against the examiners, by applying the tuning fork to their finger.[23] The quantitative method involves noting the duration of perceived vibration using a stopwatch. In order to standardize the stimulus, the examiner must strike the 128-Hz tuning fork against the palm of the free hand just hard enough to make the metal ends meet to produce a metallic clanging sound. A similar method has been previously described by in Kurtzke in the Expanded Disability Status Scale for testing sensations in patients with multiple sclerosis, and a cutoff of 10 s was suggested.[24] In a study by Oyer et al., the mean duration of perceived vibration was 10.2 s, and <8 s was taken as abnormal.[11] However, there was no comparison done with electrophysiological testing. In their study, the timed VBS of <4 s correlated with the results of the monofilaments and the risk of developing a foot ulcer.[11] In our study, the cutoff value of 8 s for timed VBS had a high sensitivity (85.0%) and hence can be used to rule out DSP. Based on our results we suggest, timed VBS testing and JPS testing are useful tools to evaluate for DSP in the setting of the neurology office, community screening, and in other resource-poor settings where further electrophysiological testing is not available. The limitations of our study include a tertiary care hospital-based setting, limited number of elderly patients and controls, and lack of data on the severity of DSP.

CONCLUSION

Neurological examination continues to have an important role in the diagnosis of DSP. For timed VBS, a duration of >8 s at the great toe was a useful test to rule out DSP, and JPS testing at the great toe, 2 or more errors in a trial of 10, is a useful test in ruling in the diagnosis of DSP.