VM is a distinct clinical entity that accounts for a high proportion of vestibular symptoms.Diagnosis of VM mainly dependson recurrent vestibular symptoms, ahistory of migraine, a temporal association between vestibular symptoms and migraine symptoms and exclusion of other reasons[2].And vestibular symptoms is based on the bárány society’s classification of vestibular symptoms such as spontaneous vertigo, positional vertigo, visually-induced vertigo,head motion-induced vertigo and head motion-induced dizziness with nausea[15].In our studies, more than half of VM patientsare found spontaneous vertigo.10–20%VM patients have other forms of vertigo. We can find thatthe most common vestibular symptom is spontaneous vertigo.Findings of most of studiesare similar our results[1, 16, 17]. Although most of VM patients have moderate to severevestibular symptoms.We still found some mild VM patients. This may be due todifferent measurements. In VM diagnostic criteria,vestibular symptoms are rated “moderate” whenthey interfere with but do not prohibit daily activities and “severe” if daily activities cannot becontinued[2].However, in our studies, vestibular symptoms is assess with DHI.In VM, duration of episodes have been reported at varying lengths, rangingfrom seconds to days and most often between minutes to hours[18].In our study, most VM patients were reported lasting minutes to hours. Thisis consistent with the previous literature[18].Besides,different migraine features may occur duringvestibular episodes, including unilaterality, pulsating quality, moderateto severe intensity,worsening with physical activity, photophobia, phonophobia and visual aura.In our study,the visual aura is infrequent in VM patients.Furman et al.reported thatVM is more common in patients without aura than in patients with aura[19].The view support our study result. We also found thatauditory symptoms is like tinnitus and hearing loss have been foundin 49% and 39% of VM patients. It is reported thatthe number of patients with auditory symptoms will be more than doubles as the progression of VM[20]. However, hearing loss does not progress to profoundlevels[21].
VM is classified entirely on the basisof clinical features as reported by the patient[21].However, VM patients can also find abnormal results in vestibular and oculomotor function test.In our study,most of VM patients have abnormal vestibular function test.It includes otolithfunction(VEMP) and semicircular canalfunction(vHITand caloric irrigation test).In VEMP,we found that oVEMP has a higher abnormal rate. After testing 39VM patients with cVEMP and oVEMP, Zaleski et al.reported that oVEMP may be especially vulnerable in patients with VM[22]. This is consistent with our result.In semicircularcanalsystem,vHIT evaluated the semicircularcanal function in response tohigh-frequency head rotationand caloric irrigation test, and low-frequency head rotation[9]. According to our study result,the abnormal rateof caloric irrigation test was higher than vHIT.It suggests that low-frequencysemicircularcanal function is vulnerablein VM patients.And the results in our studyis also in accordance with the previous reports[23, 24].Apart from vestibular function, oculomotorfunction is also a important sign in VM.In the symptom-free interval, nearly half of VM patientswere found abnormal oculomotor tests in our study. Such signsinclude spontaneous nystagmus, positional nystagmus, gaze-evoked nystagmus and smooth pursuit.In previous reports,oculomotorabnormalities were reported in 8 to 60% of VM patients[6, 25–27]. There is a wide incidence of oculomotorabnormalities.It may be relate to course of disease. Incidence rate of oculomotorabnormalities can increase over time[20].Besides,oculomotorabnormalities is especially common during attacks of VM[18]. In addition, we furtherfound thatpositional nystagmus and smooth pursuit are common in oculomotorabnormalities. It similar to previous studies[20, 28]. These results related to mechanisms of VM. Apart from central mechanisms an inner ear involvement may explain abnormal findings. Trigeminovascularreflex-mediated vasodilatation of cranial blood vessels andsubsequently plasma extravasation causing meningealinflammation are the key reasonand trigeminovascular system also innervates the inner ear[1, 19].
Medications used for migraine prophylaxis can be used totreat VM[18].In our study,we found that half of VM patientsreported good effectivenes in their symptoms through prophylactic medications after 6 monthsfollow-up.However, there are still nearly half of VM patients that requiring medication continued or medication change(partial or poor effectiveness). How to identify the possible influencing factors before preventative medications in VM. Therefore, according to vestibular and oculomotor test results, wedivided them into different subgroups.Compared with abnormal vestibular function group, we found that most of VM patients with normal vestibular function group were good effectiveness.It suggest that vestibular function abnormalities are closely related to the effectiveness of prophylaxis medication of VM.However,the effectiveness of prophylaxis medication was no significant difference between normal and abnormal oculomotor function test in VM patients. Kang et al.found that abnormal results of vHIT and caloric tests were closely related to the necessity for continued medication in VM patientsat 6-month follow-up[29]. Besides, Jung et al.also report that there was a good drug responsiveness in VM patients with normal VEMP[30]. These results were similar to ourstudy. It was proved that there is a weak effectiveness of prophylaxis medications in VM patients with abnormalvestibular function.But the specific mechanism is not clear. Future basic studies are promising in the prophylaxis medicationmechanisms of VM.
Limitations
There are some limitations in this study. First, the number of VM patients and follow-up time were insufficient. The future studywith a large samples and longer follow-up time need to furtherconfirm our results. Second, different prophylaxis medications or a combination of multiplemedications requires further evaluation. Last, future studies need to investigate the role of specific parameters in vestibular and oculomotor function tests.