Changes in auditory evoked responses during intravenous lidocaine

Objective Detection of Tinnitus Based on Electrophysiology

Tinnitus, a common disease in the clinic, is associated with persistent pain and high costs to society. Several aspects of tinnitus, such as the pathophysiology mechanism, effective treatment, objective detection, etc., have not been elucidated. Any change in the auditory pathway can lead to tinnitus. At present, there is no clear and unified mechanism to explain tinnitus, and the hypotheses regarding its mechanism include auditory plasticity theory, cortical reorganization theory, dorsal cochlear nucleus hypothesis, etc. Current theories on the mechanism of tinnitus mainly focus on the abnormal activity of the central nervous system. Unfortunately, there is currently a lack of objective diagnostic methods for tinnitus. Developing a method that can detect tinnitus objectively is crucial, only in this way can we identify whether the patient really suffers from tinnitus in the case of cognitive impairment or medical disputes and the therapeutic effect of tinnitus. Electrophysiological investigations have prompted the development of an objective detection of tinnitus by potentials recorded in the auditory pathway. However, there is no objective indicator with sufficient sensitivity and specificity to diagnose tinnitus at present. Based on recent findings of studies with various methods, possible electrophysiological approaches to detect the presence of tinnitus have been summarized. We analyze the change of neural activity throughout the auditory pathway in tinnitus subjects and in patients with tinnitus of varying severity to find available parameters in these methods, which is helpful to further explore the feasibility of using electrophysiological methods for the objective detection of tinnitus.

The effect of intravenously administered mexiletine on tinnitus-a pilot study

The effect of intravenously administered mexiletine on subjective tinnitus and hearing was studied in six patients, who initially responded positively to lidocaine. Distinct mexiletine-induced decreases in tinnitus loudness were demonstrated in three subjects, as reflected by maximum VAS (visual analogue scale) level reduction of 34%, 95%, and 100%, respectively. One subject reported change in tinnitus pitch, another one showed a slight (18% on VAS) tinnitus reduction, and one subject disclosed no effect. Side effects were seen only during one of seven infusions. Mexiletine induced shifts in pure-tone threshold, transient evoked otoacoustic emission, and acoustic reflex threshold, probably reflecting a reversible interference in the function of organ of Corti. The concentration effect relationship remained unclear and no general 'therapeutic' level could be identified. This study confirms the effect of mexiletine on the auditory function and its potential as a possible therapeutic agent or a model for further development in tinnitus pharmacotherapy.

Objective evaluation of the effects of intravenous lidocaine on tinnitus

OBJECTIVE

Tinnitus is one of the most common and distressing otological symptoms. Although numerous therapeutic modalities have been tried, there is no consensus regarding effective therapeutic agents up to now. The effects of lidocaine on tinnitus have been reported in literature using either subjective or audiologic tests. Nevertheless, the otoacoustic emissions (OAEs) have not been utilized to demonstrate lidocaine's effect on the cochlea in the English literature. The aim of this study was to evaluate the effect of lidocaine on tinnitus by considering the alterations with tinnitus, it induces on OAEs and subjective symptoms.

METHODS

This study was performed in 30 patients with tinnitus. Twenty-eight of the patients had normal hearing and two of them evidenced mild sensorineural hearing loss. To determine the severity of tinnitus, the patients were required to fill out a tinnitus scoring scale before lidocaine infusion on the same day. Then, lidocaine was administered intravenously to each patient at a dose of 1.5 mg/kg body weight over a period of 30 min. Spontaneous otoacoustic emissions (SOAEs) and distortion product otoacoustic emissions (DPOAEs) were measured three times; namely before lidocaine injection, at 25 min after injection and on the next day. The severity of tinnitus was scored again 1 d, 1 wk and 1 mo after lidocaine administration.

RESULTS

Immediately after infusion, four patients (13.3%) declared total suppression of tinnitus, whereas three patients (10%) reported only partial relief in tinnitus subjectively. The patients, who had a subjective improved response (group 1) were compared with the patients, who had no response (group 2). Statistically significant changes (p<0.05) in DPOAE response/growth or input/output (I/O) functions were observed at 1, 2, 3, 4 and 6 kHz frequencies in lidocaine responders and at 1, 2, 3, 4 and 5 kHz frequencies in no responders at different primary stimulus levels. Statistically significant changes (p<0.05) were seen at 2 kHz for 53 dB and at 3 kHz for 62 dB SPL primaries in both groups. When the significant results of these two groups were compared with each other, differences were found insignificant.

CONCLUSION

Systematic OAE measurements revealed that no changes occurred in SOAE and DPOAE levels in that alterations disappeared the next day. Subjective relief from tinnitus was stated in some of the patients and lasted for 4 wk at longest.

Effects of intravenous lidocaine overdose on cardiac electrical activity and blood pressure in the horse

This study aimed to identify blood serum lidocaine concentrations in the horse which resulted in clinical signs of intoxication, and to document the effects of toxic levels on the cardiovascular and cardiopulmonary systems. Nineteen clinically normal mature horses of mixed breed, age and sex were observed. Lidocaine administration was initiated in each subject with an i.v. loading dose of 1.5 mg/kg bwt and followed by continuous infusion of 0.3 mg/kg bwt/min until clinical signs of intoxication were observed. Intoxication was defined as the development of skeletal muscle tremors. Prior to administration of lidocaine, blood samples for lidocaine analysis, heart rate, mean arterial blood pressure, systolic blood pressure, diastolic blood pressure, respiratory rate and electrocardiographic (ECG) data were collected. After recording baseline data, repeat data were collected at 5 min intervals until signs of intoxication were observed. The range of serum lidocaine concentrations at which the clinical signs of intoxication were observed was 1.85-4.53 microg/ml (mean +/- s.d. 3.24 +/- 0.74 microg/ml). Statistically significant changes in P wave duration, P-R interval, R-R interval and Q-T interval were observed in comparison to control values, as a result of lidocaine administration. These changes in ECG values did not fall outside published normal values and were not clinically significant. Heart rate, blood pressures and respiratory rates were unchanged from control values. This study establishes toxic serum lidocaine levels in the horse, and demonstrates that there were no clinically significant cardiovascular effects with serum lidocaine concentrations less than those required to produce signs of toxicity.

Lidocaine test in patients with tinnitus: rationale of accomplishment and relation to the treatment with carbamazepine

OBJECTIVES

There is strong evidence in the literature about the effect of local anesthetics such as lidocaine in controlling tinnitus; these agents act by stabilizing hair cell membrane and cochlear nerve fibers. However, the effect of intravenous lidocaine is transient, and its oral analog (tocainide) does not have the same efficacy for long-term treatment in patients with tinnitus. Some oral anti-epileptic drugs (carbamazepine, for instance) have been used alternatively in several studies. The aim of this work is to evaluate the response to intravenous lidocaine in patients with intractable tinnitus and the effect of oral carbamazepine in long-term maintenance of tinnitus relief.

PATIENTS AND METHODS

We studied prospectively 50 patients (28 females and 22 males; mean age 50.9 years) who underwent the lidocaine test, performed by a 3-min intravenous infusion of 2% lidocaine chloridrate. The patients who experienced any relief after the test started treatment with oral carbamazepine in ascending dosages (50-600 mg/day).

RESULTS

The results were classified as tinnitus abolition (18%), marked relief (32%), partial relief (26%), unchanged (22%), or worsening (2%). The lidocaine test showed favorable results in 76% of patients, especially those with bilateral tinnitus (P < 0.001). Afterwards, 50% of patients treated with carbamazepine maintained the improvement of tinnitus (P = 0.0034).

CONCLUSION

The authors conclude that intravenous lidocaine is effective in reducing intractable tinnitus and that there is a close association between lidocaine and oral carbamazepine effects. Therefore, carbamazepine can be used for the treatment of tinnitus when the patient achieves improvement of symptom after the lidocaine test.

The effect of lidocaine on chronic tinnitus: a quantitative cerebral perfusion study

The cerebral perfusion of a 55-year-old female patient with chronic tinnitus was investigated quantitatively by single photon emission computed tomography (SPECT) with the xenon133 inhalation method. The first investigation was performed under standard conditions, the second during suppression of tinnitus with intravenous injection of lidocaine. As a reference a healthy volunteer was included under the same conditions. The global cortical perfusion was identical on both sides except for increased perfusion in the auditory cortex, especially on the right side when tinnitus lasted during the first measurement. The second investigation under treatment with lidocaine and during the tinnitus-free interval showed a decrease of the global cortical perfusion with a slightly higher value at the temporal cortex bilaterally. In comparison to the first investigation, a difference between right and left auditory cortex could no longer be demonstrated, and also the difference between regional and global perfusion decreased. A cerebral effect under treatment of tinnitus with lidocaine was shown by the quantitative measurement of brain perfusion. It is debatable whether this effect on cerebral activity results from the medication or as a reaction to the tinnitus-free interval.

Vestibular compensation in guinea pigs given intravenous lidocaine after unilateral labyrinthectomy

Intravenous lidocaine has been reported to alleviate vertigo in Meniere's disease and suggested as a possible antivertigo agent after unilateral labyrinthectomy in a study of cats. To further evaluate the effects of intravenous lidocaine on the acute phase of postural compensation, we subjected 13 pigmented guinea pigs to unilateral labyrinthectomy. Seven received intravenous lidocaine (4 mg/kg) immediately after labyrinthectomy. The other six served as controls and received an equivalent-volume injection of normal saline solution. Total body curvature, trunk curvature, yaw head tilt, and roll head tilt were measured at frequent intervals for up to 30 hours after surgery. Both groups had immediate difficulties with posturing that gradually improved. The lidocaine group tended to exhibit delayed postural compensation, but this was only statistically significant for roll head tilt. These results do not show improvement in postural compensation from unilateral labyrinthectomy after the administration of intravenous lidocaine. A species-specific effect on the vestibular pathways is suggested, and we conclude that further evaluation of lidocaine and the vestibular system is warranted.