Effect of drug therapy on compensation from vestibular injury

Management of peripheral vertigo with antihistamines: New options on the horizon

Vertigo is associated with a wide range of vestibular pathologies. It increasingly affects the elderly, with a high cost to society. Solutions include vestibular suppressants and vestibular rehabilitation, which form the mainstay of therapy. Antihistamines represent the largest class of agents used to combat vestibular vertigo symptoms. Agents targeting the H₁ and H₃ receptors have been in clinical use for several decades as single agents. Nonetheless, effective management of vertigo proves elusive as many treatments largely address only associated symptoms, and with questionable efficacy. Additionally, the primary and limiting side effect of sedation is counterproductive to normal functioning and the natural recovery process occurring via central compensation. To address these issues, the timing of administration of betahistine, the mainstay H₃ antihistamine, can be fine-tuned, while bioavailability is also being improved. Other approaches include antihistamine combination studies, devices, physical therapy and behavioural interventions. Recently demonstrated expression of H₄ receptors in the peripheral vestibular system represents a new potential drug target for treating vestibular disorders. A number of novel selective H₄ antagonists are active in vestibular models in vivo. The preclinical potential of SENS-111 (Seliforant), an oral first-in-class selective H₄ antagonist is the only such molecule to date to be translated into the clinical setting. With an excellent safety profile and notable absence of sedation, encouraging outcomes in an induced vertigo model in healthy volunteers have led to ongoing clinical studies in acute unilateral vestibulopathy, with the hope that H₄ antagonists will offer new effective therapeutic options to patients suffering from vertigo.

Betahistine Treatment in a Cat Model of Vestibular Pathology: Pharmacokinetic and Pharmacodynamic Approaches

This study is a pharmacokinetic (PK) and pharmacodynamics (PD) approach using betahistine doses levels in unilateral vestibular neurectomized cats (UVN) comparable to those used in humans for treating patients with Menière's disease. The aim is to investigate for the first time oral betahistine administration (0.2 and 2 mg/kg/day) with plasma concentrations of betahistine and its major metabolite 2-pyridylacetic acid (2-PAA) (N = 9 cats), the time course of posture recovery (N = 13 cats), and the regulation of the enzyme synthesizing histamine (histidine decarboxylase: HDC) in the tuberomammillary nuclei (TMN) of UVN treated animals (N = the same 13 cats plus 4 negative control cats). In addition the effect of co-administration of the lower betahistine dose (0.2 mg/kg/day) and selegiline (1 mg/kg/day), an inhibitor of the monamine oxidase B (MAOBi) implicated in betahistine catabolism was investigated. The PK parameters were the peak concentration (C_max), the time when the maximum concentration is reached (T_max) for both betahistine and 2-PAA and the area under the curve (AUC). The PD approach consisted at quantifying the surface support area, which is a good estimation of posture recovery. The plasma concentration-time-profiles of betahistine and 2-PAA in cats were characterized by early C_max-values followed by a phase of rapid decrease of plasma concentrations and a final long lasting low level of plasma concentrations. Co administration of selegiline and betahistine increased values of C_max and AUC up to 146- and 180-fold, respectively. The lowest dose of betahistine (0.2 mg/kg) has no effects on postural function recovery but induced an acute symptomatic effect characterized by a fast balance improvement (4–6 days). The higher dose (2 mg/kg) and the co-administration treatment induced both this acute effect plus a significant acceleration of the recovery process. The histaminergic activity of the neurons in the TMN was significantly increased under treatment with the 2 mg/kg betahistine daily dose, but not with the lower dose alone or in combination with selegiline. The results show for the first time that faster balance recovery in UVN treated cats is accompanied with high plasma concentrations of betahistine and 2-PAA, and upregulation of HDC immunopositive neurons in the TMN. The higher betahistine dose gives results similar to those obtained with the lower dose when co-administrated with an inhibitor of betahistine metabolism, selegiline. From a clinical point of view, the study provides new perspectives for Menière's disease treatment, regarding the daily betahistine dose that should be necessary for fast and slow metabolizers.

Antivertiginous drug therapy does not hinder the efficacy of individualized vibrotactile neurofeedback training for vestibular rehabilitation - a randomized trial

Vestibular rehabilitation using individualized vibrotactile neurofeedback training (IVNT) can lead to significant improvement in the postural stability of patients with vestibular symptoms of different origins. However, some of these patients have complex, severe dizziness, meaning that a pharmacological pretreatment or parallel (to vestibular rehabilitation) treatment can help them perform the rehabilitation exercises. Hence, the present study investigated the influence of a pharmacological treatment on the efficacy of vibrotactile neurofeedback training in patients with chronic, noncompensated vestibulopathies. All participants performed IVNT for ∼10 min each day for 2 weeks. In addition, every second participant was selected randomly to receive oral medication (20 mg cinnarizine and 40 mg dimenhydrinate per tablet), taking three tables per day. Trunk and ankle sway and postural stability were measured. In addition, the dizziness handicap inventory was evaluated immediately before training on the last day of training and 6 months after training. After the 10-day period of IVNT, both groups showed a statistically significant improvement in all parameters tested. A follow-up analysis after 6 months showed a long-term efficacy for the IVNT, that is, the patients remained significantly improved in their postural stability. The antivertiginous therapy did not hinder the efficacy of the IVNT. The present results indicate that IVNT even in combination with an antivertiginous drug therapy is an effective treatment regime for patients with disabling vertigo of different origins.

Comparison of the therapeutic efficacy of a fixed low-dose combination of cinnarizine and dimenhydrinate with betahistine in vestibular neuritis: a randomized, double-blind, non-inferiority study

BACKGROUND

Vestibular neuritis (VN) is a strongly disabling disease of the peripheral vestibular system. Rapid and effective relief of symptoms is important to allow patients to promptly return to normal physical activity.

OBJECTIVE

The aim of this prospective, randomized, double-blind study was to evaluate the efficacy of a fixed low-dose combination of cinnarizine and dimenhydrinate in unilateral VN in comparison with betahistine in terms of improvement of vertigo and concomitant symptoms, and performance in neurotological testing.

METHODS

Sixty-two patients were randomized to receive either cinnarizine 20 mg/dimenhydrinate 40 mg as a fixed combination or betahistine 12 mg, each three times daily for 4 weeks. Vertigo and concomitant symptoms, activities of daily living (ADL), posturography and a battery of vestibulo-ocular tests, registered by electronystagmography including spontaneous nystagmus, bithermal caloric and rotatory test, among others, were assessed at baseline (t(0)), after 1 week (t(1w)) and after 4 weeks (t(4w)). The primary endpoint was the Mean Vertigo Score (MVS) at t(1w), a composite of 12 individual scores for unprovoked and provoked vertigo, each assessed using a 10 cm visual analogue scale (VAS). Non-inferiority of the fixed combination versus betahistine would be assumed if the two-sided 95% confidence intervals (CIs) for between-group differences in MVS lay entirely below the non-inferiority margin of 1.25 (12.5% of VAS range).

RESULTS

The fixed combination led to significantly greater improvements in MVS than betahistine both at t(1w) (primary endpoint) and at t(4w) (95% CI for the difference in baseline-adjusted means -0.95, -0.64 at t(1w), -0.77, -0.44 at t(4w); p < 0.001). Vegetative symptoms and ADL also improved significantly more under the fixed combination than under betahistine at t(1w) (p < 0.001, each parameter) and t(4w) (p < 0.001 and p < 0.01, respectively), both showing a nearly complete remission at t(4w). In the two groups, pathological posturography and electronystagmography parameters normalized during the 4-week treatment. The fixed combination group showed an earlier recovery of spontaneous nystagmus than the betahistine group (t(1w), p < 0.001) and slightly higher improvements in asymmetry of rotation-induced nystagmus at t(1w) and t(4w) (p = 0.041, each time point). No significant differences were found between the treatments in abatement of spontaneous nystagmus at t(4w) and decrease of caloric lateralization or improvement of equilibrium (sensory organization test [SOT], conditions 5/6) at t(1w) and t(4w). No patient reported any adverse event.

CONCLUSION

The results showed that the fixed low-dose combination of cinnarizine and dimenhydrinate is an effective and well tolerated option for symptomatic treatment in unilateral VN. The fixed combination led to significant improvements in vertigo and ADL within the first week, and to a nearly complete recovery after 4 weeks. Neurotological testing revealed no signs of a possible detrimental influence of the 4-week treatment with the fixed combination compared with betahistine in terms of recovery of caloric responsiveness and abatement of rotation-induced nystagmus.

Principles of vestibular physical therapy rehabilitation

The use of vestibular rehabilitation for persons with balance and vestibular disorders is used to improve function and decrease dizziness symptoms. Principles of a vestibular rehabilitation program are described including common exercises and outcome measures used to report change. A review of negative and positive predictive factors related to recovery is also provided.

Failure of gamma-aminobutyrate acid-beta agonist baclofen to improve balance, gait, and postural control after vestibular schwannoma resection

INTRODUCTION

Incomplete postural control often occurs after vestibular schwannoma (VS) surgery. Customized vestibular rehabilitation in man improves and speeds up this process. Animal experiments have shown an improved and faster vestibular compensation after administration of the gamma-aminobutyrate acid (GABA)-beta agonist baclofen.

OBJECTIVE

To examine whether medical treatment with baclofen provides an improvement of the compensation process after VS surgery.

DESIGN

A time-series study with historical control.

SETTING

Tertiary referral center.

METHODS

Thirteen patients who underwent VS resection were included and compared with a matched group of patients. In addition to an individualized vestibular rehabilitation protocol, the study group received medical treatment with 30 mg baclofen (a GABA-beta agonist) daily during the first 6 weeks after surgery.

MAIN OUTCOME MEASURES

Clinical gait and balance tests (Romberg maneuver, standing on foam, tandem Romberg, single-leg stance, Timed Up & Go test, tandem gait, Dynamic Gait Index) and Dizziness Handicap Inventory. Follow-up until 24 weeks after surgery.

RESULTS

When examining the postoperative test results, the group treated with baclofen did not perform better when compared with the matched (historical control) group. Repeated-measures analysis of variance revealed no significant group effect, but a significant time effect for almost all balance tests during the acute recovery period was found. An interaction effect between time and intervention was seen concerning single-leg stance and Dizziness Handicap Inventory scores for the acute recovery period.

CONCLUSION

Medical therapy with baclofen did not seem to be beneficial in the process of central vestibular compensation.

Restoration of vestibular function: basic aspects and practical advances for rehabilitation

BACKGROUND

Normal balanced functioning of the human vestibular system is required to achieve an upright stance and locomotion, head and eye stabilization and internal spatial representation; any lesion in this system will disrupt these functions.

SCOPE

This review synthesizes previous work performed by the author and his research group in both animal models and vestibular defective patients over the last three decades. The author presents both an updated view on the basic mechanisms underlying the two main theories of vestibular compensation and his views on the principles that should guide management and rehabilitation of patients with vestibular loss.

FINDINGS

Static deficits, following the loss or disruption of vestibular functions, are fully compensated; this is explained by the vestibulo-centric theory that suggests different plastic changes occurring in the vestibular nuclei complexes. In contrast, dynamic deficits remain poorly compensated; the restoration of dynamic vestibular functions results from substitution processes and vicarious strategies. The practical advances in the rehabilitation of vestibular defective patients are as follows: (1) perform rehabilitation at an early stage; (2) favour active retraining; (3) do not use stereotyped rehabilitation programs but adapt exercises to the patients; (4) examine patients in standardized environments; (5) use both static and dynamic tests; and (6) avoid drugs with sedative effects (or limit them to the very acute stage only) and prescribe those accelerating the recovery process (e.g. betahistine dihydrochloride).

CONCLUSION

Recovery of vestibular function is greatest when early active retraining and adequate pharmacological treatments are used in combination.

Effects of Chronic Infusion of a GABAA Receptor Agonist or Antagonist into the Vestibular Nuclear Complex on Vestibular Compensation in the Guinea Pig

The aim of this study was to determine the effects of chronic infusion of a GABA(A) receptor agonist/antagonist into the ipsilateral or contralateral vestibular nuclear complex (VNC) on vestibular compensation, the process of behavioral recovery that occurs after unilateral vestibular deafferentation (UVD). This was achieved by a mini-osmotic pump that infused, over 30 h, muscimol or gabazine into the ipsilateral or contralateral VNC. Spontaneous nystagmus (SN), yaw head tilt (YHT), and roll head tilt (RHT) were measured. Infusion of muscimol or gabazine into either the ipsilateral or the contralateral VNC had little effect on SN compensation. In contrast, infusion of muscimol (250, 500, and 750 ng) into the contralateral VNC and gabazine (31.25, 62.5, and 125 ng) into the ipsilateral VNC significantly affected YHT and RHT (p < 0.05), but not their rate of compensation (p > 0.05). Interestingly, the effects of muscimol and gabazine on YHT and RHT were consistent throughout the first 30 h post-UVD. Infusion of muscimol (62.5, 125, and 250 ng) into the ipsilateral VNC and gabazine (125, 375, and 750 ng) into the contralateral VNC had little effect on YHT and RHT or their rate of compensation. These results suggest that the ipsilateral gabazine and contralateral muscimol infusions are modifying the expression of the symptoms without altering the mechanism of compensation. Furthermore, the neurochemical mechanism responsible for vestibular compensation can cope with the both the GABA(A) receptor-mediated and the UVD-induced decrease in resting activity.

Histamine and betahistine in the treatment of vertigo: elucidation of mechanisms of action

The aim of this review is to provide clinicians with a picture of the mechanisms by which: histamine and histaminergic agonists act on the vestibular system both peripherally and centrally; and histaminergic agonists and antagonists interfere with the recovery process after peripheral vestibular lesion. We have focused on betahistine, a structural analogue of histamine with weak histamine H(1) receptor agonist and more potent H(3) receptor antagonist properties, to review the currently available data on the role of the histaminergic system in the recovery process after peripheral vestibular deficits and the effects of histamine analogues in the clinical treatment of vertigo. This review provides new insights into the basic mechanisms by which betahistine improves vestibular compensation in animal models of unilateral vestibular dysfunction, and elucidates particularly the mechanisms of action of this substance at the level of the CNS. It is proposed that betahistine may reduce peripherally the asymmetric functioning of the sensory vestibular organs in addition to increasing vestibulocochlear blood flow by antagonising local H(3) heteroreceptors. Betahistine acts centrally by enhancing histamine synthesis within tuberomammillary nuclei of the posterior hypothalamus and histamine release within vestibular nuclei through antagonism of H(3) autoreceptors. This mechanism, together with less specific effects of betahistine on alertness regulation through cerebral H(1) receptors, should promote and facilitate central vestibular compensation. Elucidation of the mechanisms of action of betahistine is of particular interest for the treatment of vestibular and cochlear disorders and vertigo.

Labyrinthectomy versus vestibular neurectomy: long-term physiologic and clinical outcomes

OBJECTIVE

To determine whether long-term vestibular compensation (VC) and clinical outcomes differ after transmastoid labyrinthectomy (TML) versus retrolabyrinthine vestibular neurectomy (RVNS).

STUDY DESIGN

Prospective, observational study.

SETTING

Tertiary care, university hospital.

PATIENTS

Twenty-one subjects were studied several years after they were relieved of spontaneous episodic vertigo caused by peripheral vestibular disease by TML or RVNS.

INTERVENTIONS

All patients had undergone TML or RVNS more than 2.5 years before the study and returned for physiologic and functional studies of vestibular compensation.

MAIN OUTCOME MEASURES

Completeness of physiologic VC, as assessed by electronystagmography and rotational chair testing; performance on computerized dynamic posturography; pure-tone and speech audiometry; self-assessment of balance and hearing function with validated survey instruments.

RESULTS

There were no differences in the incidence of physiologic VC or functional recovery between the TML and RVNS subjects. Although a majority of subjects in each group had evidence of incomplete vestibular compensation, there was no difference in self-assessment of balance or hearing handicap at long-term follow-up.

CONCLUSIONS

Long-term clinical balance and hearing outcomes are equivalent when TML and RVNS successfully cure spontaneous, episodic vertigo. There is a high incidence of incomplete VC after both procedures, though this does not usually produce a significant balance handicap.

Programmatic vestibular rehabilitation

Although the use of vestibular exercises for patients with persistent vertigo and dysequilibrium has received some attention for many years, organized vestibular rehabilitation therapy programs have only recently been introduced. The benefits of such programs are becoming widely accepted. They typically involve a three-pronged approach: habituation exercises designed to facilitate central nervous system compensation by extinguishing pathologic responses to head motion, postural control exercises, and general conditioning activities. This article will describe the programmatic approach to vestibular rehabilitation, emphasizing selection criteria and reviewing results that may be anticipated when this treatment modality is used in a variety of patient populations.

Calcium antagonists and the vestibular system: a critical review of flunarizine as an antivertigo drug

Flunarizine, a diphenylalkylamine, is one of the most popular antivertiginous drugs used nowadays in France. However, until now, there are very few preliminary data about the physiological or pathophysiological functions of calcium in the vestibular system. Moreover, experimental and clinical arguments are still insufficient to clearly demonstrate that 1) flunarizine is an effective antivertiginous drug and 2) this putative antivertiginous property is really due to the anticalcic action of the drug and not to a more classical antagonistic effect on H1 receptors. Much more work is needed before accepting the indication of any anticalcic drug as an effective antivertigo treatment.

Unilateral loss of peripheral vestibular function in patients: degree of compensation and factors causing decompensation

Unilateral surgical ablation of peripheral vestibular function has been suggested for the treatment of a number of diseases that involve vestibular dysfunction. The postoperative distressing symptoms usually subside with time, whereupon the patient is said to have clinically compensated. However, even in well-compensated patients, the initial symptoms may reappear--under certain conditions that are briefly discussed (decompensation)--and, in addition, vestibular gaze stabilization deficits, (apparently permanent) appear whenever moderately rapid head movements are imposed. Thus, surgical ablation of unilateral peripheral vestibular function should not be considered "a treatment of choice," and should be performed in only carefully selected cases.