Acute peripheral vestibulopathy (APV) is characterized by an episode of acute, prolonged vertigo caused by peripheral vestibular tone imbalance, and patients typically experience severe vertigo (spinning/swaying sensation), imbalance, nausea, and vomiting.1 Clinical and laboratory evaluations have shown various combinations of vestibular imbalance, including mixed horizontal-torsional nystagmus beating away from the lesion side and ipsilesional caloric paresis, abnormalities in head impulse test (HIT) results, the ocular tilt reaction, and subjective visual vertical (SVV) tilt, and decreased vestibular-evoked myogenic potentials (VEMPs).2 However, the diagnosis is occasionally challenging due to atypical manifestations, particularly in APV patients in which horizontal canal function is spared.3456 We report a patient presenting with acute vertical diplopia as a major manifestation of APV.

A 63-year-old female presented with vertical diplopia and mild imbalance that first appeared 3 days previously. She denied any preceding upper respiratory infection or diarrhea. An examination revealed a skew deviation with vertical displacement in the prism cover test (2 prism diopters of hypertropia in the left eye). There was no spontaneous nystagmus or head tilt. The results of bedside horizontal HITs were normal. She veered to the left while tandem walking. Other neurological examinations produced unremarkable finding. The Hess screen test showed a skew deviation with a hypertropic left eye (Fig. 1A), and fundus photography revealed extorsion (20°) of the right eye and intorsion (2°) of the left eye [pathological ocular torsion is defined when the eye shows any intorsion (<0°) or extorsion of >12.6°] (Fig. 1B). The patient had rightward SVV tilt with binocular viewing (10.0°; normal range −3.0° to 3.0°, a negative value indicates a counterclockwise tilt). Video HITs disclosed decreased a vestibulo-ocular reflex (VOR) gain with corrective catch-up saccades of the right posterior semicircular canal (PC) (Fig. 1C), while bithermal caloric tests and air-conducted cervical VEMP (Fig. 1D) tests produced symmetrical results. Brain MRI scans including DWI with 3-mm-thick sections performed at 3 and 10 days after the onset of symptoms were unremarkable. The symptoms rapidly resolved 3 days later, and the findings for video HITs, ocular torsion, and SVV tilt returned to normal.

Skew deviation is vertical misalignment of the eyes caused by a supranuclear disorder involving the otolith-ocular pathways. The phenomenon is mostly seen in the brainstem or cerebellar lesions, and it is one of the important signs suggesting stroke in a part of the head impulse, nystagmus, and test of skew (HINTS).7 There are rare cases of skew deviation also being observed in the acute stage following unilateral peripheral vestibular surgery, such as labyrinthectomy or vestibular neurectomy, or vestibular neuritis.489

Our patient developed acute vertical diplopia as a major manifestation of APV. A neurootological evaluation produced findings suggestive of the selective involvement of the unilateral PC and utricle. Remarkably, there were no typical vestibular symptoms or signs of APV such as vertigo with nausea/vomiting, spontaneous nystagmus, or abnormality in horizontal HITs. Previous cases with skew deviation following unilateral peripheral vestibulopathy presented with predominantly vestibular symptoms or signs.310 Patients with acute vertical diplopia due to skew deviation with intact horizontal semicircular canal function generally require a workup for brainstem or cerebellar stroke. However, the normal results of initial and follow-up MRI, and the decreased VOR gain of the unilateral PC in our patient suggest the presence of partial APV selectively affecting the utricle and PC. Cases with partial APV selectively affecting vestibular structures have been recently reported.45611

Both skew deviation and trochlear nerve palsy present with hypertropia in the primary position. Incyclotorsion of the hypertropic eye supports skew deviation rather than trochlear nerve palsy, since unilateral trochlear nerve palsy results in hypertropia and the affected eye being unable to incyclotort.12 Furthermore, the SVV of the patient was tilted toward the contralateral side of the hypertropia.13