Dear Sirs,

Vestibular paroxysmia (VP) is characterized by brief and recurrent vertigo that respond well to carbamazepine or oxcarbazepine [1]. An assumed mechanism is a neurovascular cross-compression (NVCC) of the vestibular nerve offended by a vascular loop [2]. Typewriter tinnitus refers to unilateral staccato sounds, and has also been attributed to NVCC of the cochlear nerve [2, 3]. Association of these two conditions has rarely been recognized [4]. We herein describe a patient with typewriter tinnitus and VP due to a NVCC of the vestibulocochlear nerve with a literature review.

A 43-year-old man was referred for management of intermittent attacks of vertigo and staccato sounds in his right ear for 5 months. The attacks occurred 10–20 times a day, and each attack lasted less than 1 min. The tinnitus was always time-locked to the vertiginous spells with an abrupt onset and cease. The attacks were often triggered by bending his head and accompanied by oscillopsia and unsteady gait. He had no symptoms between the attacks, but showed spontaneous nystagmus beating leftward, upward, and counterclockwise (upper poles of the eyes beating to the left ear) without visual fixation (Fig. 1A). Horizontal head shaking increased the spontaneous left beating nystagmus, but hyperventilation, mastoid vibration or positional maneuvers did not alter the nystagmus. Video head impulse tests (HITs) showed a decreased gain of the vestibulo-ocular reflex (VOR) for right horizontal semicircular canal with overt saccades (Fig. 1b). The results of other audiovestibular function tests were all normal. Constructive interference in steady-state MRI documented a NVCC and mild angulation of the right vestibulocochlear nerve by a complex of the anterior and posterior inferior cerebellar arteries (Fig. 1c–e). Unfortunately, we did not have an opportunity to evaluate the patient during the attacks.

Fig. 1
figure 1

a Video-oculography shows spontaneous nystagmus beating to the left (\(1.5 ^\circ /\mathrm{s}\)), upward (\(1.5 ^\circ /\mathrm{s}\)), and counterclockwise (\(1.5 ^\circ /\mathrm{s}\)) without visual fixation. RH = horizontal position of the right eye, RV = vertical position of the right eye, RT = torsional position of the right eye. Upward deflection in each trace indicates rightward, upward, and clockwise eye motion. b Video head impulse tests show overt saccades during stimulation of the right horizontal semicircular canal with a decreased gain at 0.77 (normal = 0.88–1.06). c–e. Constructive interference in steady-state images of magnetic resonance imaging of the brain and internal auditory canal (C) and magnified views (d, e, the white square in the Figure C) disclosed the AICA-PICA loop crossing the cisternal segment of the right vestibulocochlear nerve and causing a mild angulation of the nerve (red arrow: vascular complex of AICA-PICA, yellow arrow: the vestibulocochlear nerve)

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He started carbamazepine 200 mg daily with a minimal reduction of the tinnitus and subsequent discontinuation. Oxcarbazepine 300 mg twice a day was also ineffective. Re-initiation of carbamazepine at an escalated dose of 300 mg twice a day resulted in resolution of the symptoms, but the interictal spontaneous nystagmus persisted.

Our patient presented with paroxysmal attacks of vertigo and typewriter tinnitus that resolved with carbamazepine. The attacks were mostly spontaneous, but often triggered by head position changes, with an imaging evidence of NVCC. These findings are consistent with the diagnosis of VP according to the criteria proposed by the Barany Society [5]. Given the characteristics of typewriter tinnitus, the paroxysmal nature with an excellent response to carbamazepine, the tinnitus may be ascribed to NVCC affecting the cochlear nerve [2, 6]. Recent studies showed that the psychoacoustic characteristics and a good response to carbamazepine are more reliable for diagnosing NVCC of the cochlear nerve than the radiologic findings [4]. In our patients, the co-occurrence of typewriter tinnitus and VP and simultaneous resolution of these symptoms after carbamazepine trials indicates a common mechanism of NVCC in these paroxysmal disorders. The rare occurrence of typewriter tinnitus in comparison to VP, however, indicates a different susceptibility for ephaptic discharges between the vestibular and cochlear nerves. The larger size of cochlear nerve fibers than the vestibular ones may reduce the likelihood of ephaptic discharges in these nerve fibers [7, 8]. Otherwise, any difference in the reorganization thresholds, which is believed to play a role in inducing symptoms in NVCC, may result in different occurrences of ephaptic discharges between the cochlear and vestibular nerves [9, 10].

Our patient showed the findings of right peripheral vestibular hypofunction (left beating spontaneous nystagmus and positive HITs for the right horizontal canal) between the attacks. These interictal findings indicate chronic vestibular hypofunction from NVCC, inducing demyelination and resultant conduction block in addition to ephaptic discharges [11]. Indeed, patients with VP have showed various patterns of audiovestibular abnormalities between the attacks [1, 12,13,14,15]. Preserved audiometric function in our patient indicates that cochlear damage is not mandatory for generation of tinnitus [6, 16].

We were able to find 21 patients with combined VP and typewriter tinnitus in the literature (Table 1) [2, 3, 4, 17,18,19,20]. Except one with bilateral NVCC on MRIs, all patients showed an imaging evidence of NVCC on the side of tinnitus. Of the 15 patients who had audio-vestibular function tests, 6 showed abnormal results on the symptomatic side. Most patients (19/21, 90%) showed an excellent response to carbamazepine or oxcarbazepine. This report highlights the etiological association of VP and typewriter tinnitus, and proper titration of carbamazepine or oxcarbazepine in managing the patients with these disorders.

Table 1 Summary of the findings in patients with combined vestibular paroxysmia and typewriter tinnitus
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