Background
Dizziness and vertigo are frequent symptoms accompanying primary headache disorders, especially migraine [1]. Migraine has long been associated with various vestibular symptoms and several vestibular syndromes [2]. Additionally, several studies have identified several vestibular laboratory abnormalities in migraineurs [3].
Of the various methods used to evaluate the vestibular system, vestibular evoked myogenic potential (VEMP) is a non-invasive and simple clinical test. Cervical VEMP (cVEMP) represents an uncrossed vestibulo-collic reflex, which assesses saccular function, the inferior vestibular nerve and vestibular nuclei, and serves as a pathway through the lower brainstem to the motor neurons of the sternocleidomastoid muscle [4]. The more recently described ocular VEMP (oVEMP), a manifestation of a crossed vestibulo-ocular pathway, reflects predominantly utricular function and involves the medial longitudinal fasciculus, oculomotor nuclei and nerves, and extraocular muscles following activation of the vestibular nerve and nucleus [4, 5]. While cVEMP descends via the vestibulospinal tract through the lower brainstem, oVEMP ascends via the medial longitudinal fasciculus through the upper brainstem. Additionally, recent studies suggest that oVEMP is produced by otolith afferents in the superior vestibular nerve division, whereas cVEMP, evoked by sound, is believed to be an inferior vestibular nerve reflex [6]. Using oVEMP and cVEMP together allows for the evaluation of both ascending and descending vestibular pathways in the brainstem and identifies a higher percentage of abnormalities [4]. Thus, the combined measures of oVEMP and cVEMP provide complementary information.
VEMP presentation differs in individual patients according to the method used for assessment, diagnosis of migraine subtype, and the presence of vestibular symptoms, as reported in literature. Several authors have reported absent or delayed cVEMPs [7–10], whereas others have found cVEMPs of normal latency but reduced amplitude in migraineurs [11, 12]. In contrast with most previous studies, a normal interictal cVEMP profile was reported in patients with migraine with or without aura and vestibular migraine [13]. Recently, interest in oVEMP studies for migraine has increased. High rates of absent oVEMP and higher amplitude asymmetry ratios or reduced amplitudes have been shown in vestibular migraine (VM) [14, 15], whereas prolonged latency and lower amplitudes were found in migraineurs without vestibular symptoms [16].
Although previous VEMP reports have been inconsistent, VEMP remains the easiest and simplest method for measuring vestibular activity in clinical practice to date. Measurement of both ocular and cervical VEMPs provides more information because the results are complementary. Additionally, several studies on patients with migraine without vestibular symptoms have reported vestibular deficits in various vestibular function tests. In particular, findings such as defective oculomotor function, dysfunctional equilibrium, and peripheral and central vestibular deficits have been described [17–21]. Patients with tension-type headache (TTH) often report balance disorders or subjective imbalance [22, 23]. However, little is known about vestibular function in those with TTH without manifested vestibulopathy.
Thus, we hypothesized that migraineurs with no accompanying vestibular symptoms exhibit subclinical vestibular dysfunction. We investigated vestibular function using ocular and rectified cervical VEMP methods in patients with migraine without aura and those with episodic TTH during headache-free periods.