Genetic aspects in migraine including vestibular migraine were reviewed. Migraine is one of the representative primary headache disorders, however, its pathophysiology still remains to be clarified. Concerning migraine, there are some genome-wide association studies. In such studies, at a total of 12 loci, significant association with migraine susceptibility has been identified. Most of them are related to synaptic function. In familial hemiplegic migraine (FHM), one of the specific types of migraine, mutated genes have been identified. Episodic ataxia may suggest the need for genetic studies in vestibular migraine or migraine-associated vertigo, because some types of EA, EA2 and EA3, show episodic vertigo and migraine. Interestingly, the mutated gene in EA2 is CACNA1A, which is the same as in FHM1. Probably, genes related to ion channels, which will affect synaptic functions, play an important role in migraine including vestibular migraine. Vestibular migraine and Menière's disease may have some common aspects from the viewpoint of channelopathy.
There are some cases of unilateral vestibular disorder without a confirmed diagnosis such as benign paroxysmal positional vertigo and Menière's disease. We performed a retrospective study to determine the cause of such unilateral vestibular disorders in patients. We investigated vertiginous outpatients who visited our clinic from Jan. 2011 to Feb. 2014. Eighty-nine patients were diagnosed as having unexplained unilateral vestibular disorders after equilibrium function tests. The diagnosis of a vestibular disorder is mainly facilitated by the demonstration of canal paresis with the caloric test. Temporal bone high-resolution CT was adapted in this study because we considered the possible presence of a unique anatomical feature of these patients. The patients showed a high rate of a high jugular bulb (HJB) with temporal bone CT findings compared to control cases. The medial type of HJB is significantly consistent with the affected side. In particular, all cases in which the jugular bulb diverticulum was observed and showed contact with the peripheral organs (vestibular aqueduct, cochlear aqueduct, posterior semicircular canal, and internal auditory meatus) in the image, were consistent with the affected side. The medial type of HJB was considered to be one of the anatomical predispositions related to vestibular disorder onset.
Bilateral vestibular failure causes movement-dependent postural vertigo, unsteadiness of gait, and in serious cases patients complain of blurred vision while walking (known as the jumbling phenomenon). This condition is defined as bilateral vestibulopathy and its diagnostic criteria have been cited in various professional publications. These criteria include, symptoms, bedside evaluation (e.g., Head Impulse Test), laboratory tests (e.g., caloric tests) and other causes excluded. On the other hand, in Japan, the Peripheral Vestibular Disorder Research Committee has proposed a set of diagnostic criteria for bilateral vestibular losses, which is based solely on the result of an ice-water caloric test, regardless of whether the patient has the characteristic symptoms or not. The purpose of this retrospective study was to clarify the relationship between the vestibular failure tested by both the caloric test and video Head Impulse Test (vHIT), and the presence of symptoms characteristic of bilateral vestibulopathy. A total of 210 patients were screened during the study period. Eight patients were included in this study who showed bilateral absent caloric responses to the ice-water caloric test due to peripheral vertigo. Among these 8 patients, only 3 patients complained of the jumbling phenomenon and vHIT showed a bilateral profound vestibular deficit. vHIT did not show any bilateral profound vestibular deficit in the other 5 patients. These results show that the abnormal caloric responses may not have clinical significance in some cases. The authors believe that bilateral vestibulopathy should be considered first with patients who have characteristic symptoms. Furthermore, they should be tested by a combination of 2 test batteries (the ice-water caloric test and vHIT) to make a proper diagnosis.
The aim of this study was to classify unilateral vestibular neuritis (VN) with caloric testing, cervical vestibular evoked myogenic potentials (C-VEMPs), ocular vestibular evoked myogenic potentials (O-VEMPs), and the video head impulse test (vHIT). Eight Patients (3 males and 5 females, mean age 55.6 years) with VN were studied. cVEMP and oVEMP (105 dBSPL 500 Hz short tone burst stimulation) were recorded. The caloric test and vHIT for the 3 semicircular canal were performed. The caloric test, cVEMP and oVEMP in combination with vHIT were able to allow the classification of 4 types of VN: entire VN, superior VN, inferior VN, and ampullary VN. In our case, 75% of the cases were entire VN, 12.5% were superior VN, and 12.5% were inferior VN. Three patients had only deficits of the horizontal and/or inferior semicircular canals or their ampullary nerves. One of eight VN patients had symptoms similar to benign paroxysmal positional vertigo after three weeks onset of VN. The results lead us to believe that clinical VN comprises vestibular neuritis and vestibular labyrinthitis. Currently, in Japan it would be essential that there is canal paresis in caloric test for VN diagnosis. We hope to include inferior VN within the diagnosis criteria of VN in the near future.
The head impulse test (HIT) and caloric test are important tests when examining for vestibular deficits. The HIT has a moderate sensitivity (35-45%) and high specificity (90%) compared with the caloric test. In 2009, the video Head Impulse Test (vHIT) was developed that can detect covert catch up saccades which can hardly be seen with the naked eye and has better sensitivity and specificity than the HIT. However, no studies have been conducted to evaluate the performance of vHIT in a Japanese population. In the caloric test, the monothermal stimulation technique is widely used in Japan. On the other hand, the bithermal stimulation technique is used worldwide with the exception of Japan. The objective of the present study was to evaluate the performance of the vHIT and monothermal cool caloric test (MCCT) mutually in a Japanese population. The sensitivity of the vHIT was 62.6% and specificity was 86.2%. The area under the receiver operating characteristic curve in the MCCT was 0.892 using VOR gain as the dependent variable, and 0.849 using CUS as the dependent variable. The vHIT is a specific and fast test to detect vestibular deficits using angular acceleration stimulation, and MCCT decreases test time and side effects without reducing sensitivity of the caloric test in bithermal stimulation.