Expert Consensus on Diagnosis of Isolated Otolith Dysfunction

The vestibular end organs in each inner ear include three semicircular canals and two otolith organs. The semicircular canals detect rotational movements of the body, while the two otolith organs, the utricle and saccule, sense linear acceleration. Clinically, some patients with dizziness or vertigo present with symptoms such as translation, tilt, etc., rather than the common vestibular symptoms of visual rotation. In these cases, vestibular function tests do not show damage to the semicircular canals, but rather damage to the otolith organs. As clinical practice in vestibular medicine has progressed, patients with these symptoms have increasingly sought consultation at dizziness clinics. Reports of cases with isolated otolith dysfunction have also gradually increased, and recently, relevant clinical studies and diagnostic criteria have been reported internationally. To enhance recognition of this vestibular syndrome and standardize clinical work, this consensus has been established.

Definition

Isolated otolith dysfunction (iOD) is a group of vestibular syndromes of unknown cause, clinically characterized by sensations of translation, tilt, or floating, as well as decreased visual sensitivity during head movements. Vestibular function tests show normal semicircular canal function but abnormal otolith function, necessitating the exclusion of other vestibular diseases. iOD has also been referred to as idiopathic otolith vertigo, idiopathic otolith-specific vestibular dysfunction, and idiopathic utricular dysfunction.

Epidemiology

Due to varying diagnostic criteria reported by different sources, there is currently no definitive epidemiological data available. Retrospective studies abroad indicate that among patients attending dizziness specialty clinics with dizziness as the primary complaint, iOD accounts for approximately 2%.

Anatomy and Physiology of Otolith Organs

3.1 Peripheral Part

The saccule and utricle are located within the vestibular sac and are filled with endolymph. The sensory maculae are located on the anterior upper wall of the saccule and the upper end of the utricle, with the saccular macula and utricular macula arranged in two mutually perpendicular planes. When upright, the saccular macula is in the sagittal plane, primarily sensing vertical linear acceleration. The utricular macula is parallel to the horizontal semicircular canal, mainly sensing horizontal linear acceleration. The hair cells within the maculae are arranged in a polarized manner along the striola and can sense linear acceleration stimuli in three-dimensional directions.

When the head is stationary and upright, the vestibular afferent nerve fibers innervating the maculae exhibit spontaneous firing, and under normal conditions, the discharge frequencies of the maculae on both sides are symmetrical. When function on one side is impaired, the asymmetry of afferent information from both otolith organs to the central nervous system leads to errors in the brain’s judgment of the gravity line, resulting in clinical symptoms such as abnormal tilt or translation; simultaneously, due to the ocular tilt reaction, patients may experience transient diplopia or a subjective tilt of the visual gravity line.

3.2 Central Part

The central pathways for otolith signal transmission largely overlap or run parallel to those of the semicircular canals. Signals from the vestibular nuclei ascend via the medial longitudinal fasciculus, Deiters’ ascending tract, or the brachium conjunctivum to the oculomotor nuclei and vestibular cortex, mediating the translational vestibulo-ocular reflex (tVOR) and forming vestibular sensations; signals from the vestibular nuclei descend via the medial longitudinal fasciculus and vestibulospinal tract to the cervical and thoracolumbar spinal cord, mediating the vestibular-ocular reflex and vestibulospinal reflex. The vestibulocerebellum and other brainstem structures, except for the vestibular nuclei and oculomotor nuclei, form multisynaptic connections with the aforementioned direct vestibular pathways, participating in and regulating the vestibulo-ocular reflex and vestibulospinal reflex.

When the head is laterally accelerated or tilted, the hair cells in the utricular macula become excited, and the nerve impulses are transmitted through three synapses or multisynaptic connections, ultimately resulting in the eyes moving in the opposite direction of the head movement. Because tVOR involves multisynaptic connections, the latency of eye movements is slightly longer than that mediated by the semicircular canals. The excitatory signals from the utricular macula also project to the anterior horn cells of the cervical spinal cord on the same side, causing simultaneous contraction of the neck flexors and extensors on the same side, leading to tilting of the neck towards the same side; when both saccule maculae are excited, the neck extensors are activated, and the flexors inhibited, resulting in neck extension in the sagittal plane. Excitatory signals from the otolith organs via the vestibulospinal tract facilitate the tonus of the trunk extensors on the same side; in addition, through the brainstem reticular formation and reticulospinal tract, the otolith organs can indirectly regulate muscle tone in the trunk and proximal limbs, participating in postural reflexes. Signals from the otolith organs also project to the central autonomic nervous system, participating in vestibulo-autonomic reflex activities, leading to changes in blood pressure and heart rate, nausea, vomiting, and reactions of fear and anxiety.

Clinical Manifestations

Non-rotational dizziness or vertigo: iOD often presents as non-rotational dizziness or vertigo. Common symptoms include a sense of self-tilt, up-down movement, a feeling of falling, or floating, as if standing on a moving ship’s deck or stepping on soft ground, leading to disorientation. A minority of patients may experience rotational vertigo. The duration of dizziness typically ranges from a few minutes to several hours; in some patients, it can be transient, while in very few cases, symptoms may persist for 1 day. Dizziness is often spontaneous, and changes in position or active movement may trigger it.

Vestibular-visual symptoms: Patients may experience decreased dynamic visual sensitivity during head movements, manifested as oscillopsia or transient diplopia in the vertical direction; in near-visual environments, due to abnormal subjective visual gravity lines, objects may appear tilted.

Postural symptoms: Patients may exhibit body tilting or leaning towards the affected side when walking in a straight line or during the Romberg test.

Ocular tilt reaction: The tilt of the head to one side, the contralateral ocular tilt reaction, and the rotation of the eyeballs are collectively referred to as the ocular tilt reaction (OTR). Lesions in the peripheral pathways of the utricle generally result in OTR towards the affected side. Abnormal tVOR can lead to contralateral eye tilt in the vertical direction and conjugate rotation of both eyes; abnormalities in the vestibular-cervical reflex can cause the head to tilt towards one shoulder, referred to as head tilt reaction.

Evaluation of Vestibular Function

The diagnosis of iOD relies on vestibular function tests. Basic tests include vestibular evoked myogenic potentials (VEMP), caloric tests, and video head impulse tests (vHIT). Optional tests include subjective visual vertical tests (SVV), rotational tests, and balance function tests.

5.1 Semicircular Canal Function Testing

This includes caloric tests, vHIT, and rotational tests. The results of semicircular canal function tests in iOD patients are normal; specific testing methods and evaluation criteria are detailed in the “Expert Consensus on Vestibular Function”.

5.2 Otolith Function Testing

5.2.1 VEMP

VEMP is the primary method for assessing otolith function, with cVEMP reflecting the function of the ipsilateral saccule and vestibular nerve, and oVEMP reflecting the function of the contralateral utricle and vestibular nerve. VEMP evaluation indicators include amplitude, latency, and threshold. Absolute amplitude is affected by muscle tone, and clinically, relative amplitude, i.e., the interaural asymmetry ratio (IAR), is primarily analyzed. Failure to elicit unilateral or bilateral waveforms, or an IAR exceeding the normal range, indicates otolith system dysfunction; abnormal latencies are primarily seen in central lesions of the otolith system. Generally, an IAR of cVEMP amplitude exceeding 33% and oVEMP amplitude exceeding 40% is considered abnormal in healthy adults. The stimulus sound for both cVEMP and oVEMP is a 500 Hz short pure tone, with a stimulation rate of about 5 times/s and 100-200 repetitions. The high-pass cutoff frequency and low-pass cutoff frequency can be set to 10 Hz and 1000 Hz, respectively, with a recommended window time range of -20 to 60 ms. cVEMP recording electrodes are placed on the upper 1/3 of both sternocleidomastoid muscles, the reference electrodes on the sternum or the inner side of the right wrist, and the common electrodes on the midline of the forehead. The recommended position for patients is sitting with the neck turned or supine with the head raised, while monitoring and recording the tone of the sternocleidomastoid muscle. oVEMP recording electrodes are placed at the midpoint of the lower edge of the orbit, the reference electrodes 1-2 cm below the recording electrodes, and the grounding electrodes on the forehead or chin. It is recommended to use a sitting position with the head upright in the midline, and the subject gazing 30° upwards. Due to the decreased elicitation rate and amplitude of oVEMP induced by air-conducted sound stimulation in the elderly, bone-conducted vibration stimulation (such as bone-conduction headphones or vibrators) can be added to induce oVEMP.

5.2.2 Subjective Visual Vertical Line Test

SVV and subjective visual horizontal line tests (SVH) are convenient and quick clinical methods for assessing the function of the utricle and its pathways. The deviation angle can reflect the asymmetry of bilateral utricular function and is influenced by the central vestibular compensation state. This test is used to assess the static tension balance state of bilateral utricles and can be combined with oVEMP to detect the functional state of the utricle and its nerve pathways. In normal individuals, the SVV deviation angle is usually within ±2.0°-2.5°. The direction of SVV deviation is related to the site of the lesion.

5.3 Balance Function Testing

Methods for evaluating postural reflexes and balance function mainly include static postural recording and dynamic postural analysis, the latter including sensory organization tests (SOT), clinical tests of sensory integration of balance (CTSIB), etc.

In the presence of disturbances to visual and proprioceptive inputs, sway in the coronal plane is sensitive for detecting utricular lesions, while sway in the sagittal plane is sensitive for detecting saccular lesions, and SOT is sensitive for detecting combined lesions (utricle-saccule).

The significance of balance function testing lies in the functional evaluation of iOD and monitoring the efficacy of vestibular rehabilitation treatment.

Clinical Diagnosis

The clinical diagnosis of iOD must meet all three recommended diagnostic criteria: ① Spontaneous, positional, or head movement-induced sensations of external or self-motion, feelings of tilt, lateral motion, or floating, and decreased dynamic visual sensitivity; ② Normal caloric tests and vHIT, with abnormal VEMP (primarily based on amplitude asymmetry ratio); ③ Cannot be better explained by other diagnoses. Scholars abroad have proposed graded diagnostic criteria for iOD (definitive diagnosis and suspected diagnosis), but based on the current clinical diagnosis and treatment situation in China, experts have discussed and temporarily decided not to implement graded diagnosis, only providing recommendations for definitive diagnosis. iOD is a diagnosis of exclusion; if a patient has an established diagnosis of known dizziness or balance dysfunction, along with abnormal VEMP and normal caloric tests and vHIT function, a diagnosis of iOD is not recommended.

Differential Diagnosis

The clinical features of iOD include non-rotational dizziness or vertigo and postural abnormalities, which need to be differentiated from other vestibular diseases that cause similar symptoms. For patients with acute onset, the possibility of central lesions should be considered.

7.1 Benign Paroxysmal Positional Vertigo

Benign paroxysmal positional vertigo (BPPV) is also known as canalithiasis and can be easily confused with iOD by name. Some patients may experience feelings of instability or floating during the course of the disease (before and after canalith repositioning treatment), and VEMP abnormalities may be observed during examination. The key points for differentiation are the characteristic clinical manifestations and signs of BPPV, which are brief episodes of positional vertigo induced by changes in head position relative to gravity, and the characteristic positional nystagmus and vertigo induced by positional testing. The relationship between otolith dysfunction in BPPV and iOD needs further study.

7.2 Meniere’s Disease and Tumarkin’s Otolith Crisis

Tumarkin’s otolith crisis, also known as drop attacks, refers to sudden falls while walking or standing without any warning, after which the patient can immediately get up and continue activities; the episodes are brief, with no loss of consciousness and typically no vertiginous episodes. Causes include both non-ear and ear-related diseases. Meniere’s disease is a common cause, accounting for 4.1% of the initial symptoms of Meniere’s disease. Its pathogenesis is related to otolith dysfunction, with VEMP abnormalities observed; however, patients with Meniere’s disease also experience severe rotational vertigo and fluctuating hearing loss, thus not meeting the diagnostic criteria for iOD.

7.3 Persistent Postural-Perceptual Dizziness

Persistent postural-perceptual dizziness (PPPD) is a chronic vestibular dysfunction characterized by persistent non-rotational dizziness and postural instability lasting more than 3 months, with symptoms often exacerbated in complex visual backgrounds and during active or passive movements. It often follows acute or episodic vestibular diseases, and some patients may have a history of acute stress events or medical conditions.

Some PPPD patients may show VEMP abnormalities. The relationship between otolith dysfunction in PPPD and iOD needs further study.

7.4 Vestibular Migraine

Vestibular migraine (VM) is a disease characterized by recurrent dizziness or vertigo, which may be accompanied by nausea, vomiting, or headache. Some VM patients may show prolonged VEMP latencies, suggesting possible damage to the central pathways of the otolith organs, but specific localization is challenging.

7.5 Bilateral Vestibulopathy

Bilateral vestibulopathy (BVP) primarily presents as postural instability and oscillopsia, with some patients having unknown causes. Patients with BVP have significantly reduced function in the semicircular canals and their pathways. Some BVP patients may only have abnormal VEMP results, indicating selective involvement of the otolith organs and pathways.

7.6 Inferior Vestibular Neuritis

Inferior vestibular neuritis (IVN) is clinically rare, with vestibular function tests showing normal caloric tests but abnormal cVEMP. Unlike iOD, IVN patients also exhibit the following symptoms and signs: ① Acute vertigo accompanied by nausea/vomiting and imbalance; ② Spontaneous torsional downbeat nystagmus; ③ Abnormal vHIT only in the posterior semicircular canal; ④ No central lesions.

7.7 Central Diseases

Acute infarction or hemorrhage in the thalamus or vestibular cortex may present with only postural instability, visual tilt, or SVV abnormalities, sometimes accompanied by OTR manifestations, without focal neurological deficits such as limb paralysis, sensory disturbances, or aphasia, necessitating imaging studies to differentiate from iOD.

Lesions in the dorsal tegmentum of the brainstem and the cerebellum may present with OTR or SVV abnormalities in approximately one-third to half of patients, but patients often have accompanying limb paralysis, dysarthria, or persistent diplopia, which can be differentiated from iOD through imaging studies.

Questions and Prospects

Due to the limited objective examination methods, such as the sensitivity and specificity of VEMP tests not being sufficiently high, the inability to popularize variable radius centrifuge chairs and large linear acceleration devices limits their clinical application, and is insufficient to enhance understanding of otolith system diseases. Currently, the diagnostic criteria for iOD are still primarily based on symptom observation and the exclusion of other vestibular diseases, requiring special attention to differential diagnosis to avoid overgeneralization of the iOD diagnosis. In the future, as understanding of the neuroanatomy and physiology of otolith signal transmission pathways improves and as technological advancements in manufacturing develop, there will be significant advancements in the understanding of iOD.

Guideline/Consensus Committee Members

(Sorted by stroke order of surnames)

Yu Gang (Dizziness Center, Shandong Provincial Hospital), Yu Hong (Department of Otolaryngology-Head and Neck Surgery, First Hospital of Jilin University),Yu Limin (Department of Otolaryngology-Head and Neck Surgery, Second Affiliated Hospital of Harbin Medical University), Wei Xudong (Department of Otolaryngology-Head and Neck Surgery, Gansu Provincial People’s Hospital), Wang Jin (Department of Neurology, First Affiliated Hospital of Guangxi Medical University), Wang Liyi (Department of Otolaryngology, Beijing Hospital), Wang Zhenhua (Department of Neurology, Weifang Traditional Chinese Medicine Hospital, Shandong Province), Wang Haitao (Department of Otolaryngology-Head and Neck Surgery, Second Hospital of Jilin University), Yin Shihua (Department of Otolaryngology-Head and Neck Surgery, Second Affiliated Hospital of Guangxi Medical University), Deng Anchun (Department of Otolaryngology-Head and Neck Surgery, Xinqiao Hospital, Army Medical University), Zuo Wenqi (Department of Otolaryngology, First Affiliated Hospital of Chongqing Medical University), Lu Wei (Department of Otolaryngology-Head and Neck Surgery, First Affiliated Hospital of Zhengzhou Medical University), Lu Wei (female), (Department of Neurology, Second Affiliated Hospital of Central South University), Fu Rong (Department of Neurology, Second People’s Hospital of Guiyang), Fu Jin (Department of Neurology, Second Affiliated Hospital of Harbin Medical University), Bi Guorong (Department of Neurology, Shengjing Hospital of China Medical University), Bi Jingtang (Department of Otolaryngology-Head and Neck Surgery, Beijing Tongren Hospital, Capital Medical University), Zhu Qingwen (Department of Otolaryngology-Head and Neck Surgery, Second Affiliated Hospital of Hebei Medical University), Wu Weijing (Department of Otolaryngology-Head and Neck Surgery, Second Affiliated Hospital of Central South University), Ren Tongli (Department of Otolaryngology, Eye, Ear, Nose, and Throat Hospital, Fudan University), Ren Lili (Department of Otolaryngology-Head and Neck Surgery, PLA General Hospital), Liu Xingjian (Department of Otolaryngology-Head and Neck Surgery, PLA General Hospital), Liu Xiuli (Department of Otolaryngology-Head and Neck Surgery, First Affiliated Hospital of Dalian Medical University), Liu Chunling (Department of Neurology, Second Affiliated Hospital of Zhengzhou University), Liu Xiaowen (Department of Otolaryngology, Second Hospital of Lanzhou University), Liu Peng (Department of Neurology, Shaanxi Provincial People’s Hospital), Tang Yong (Clinical Medical College, Changchun University of Traditional Chinese Medicine), Sun Xingang (Department of Neurology, Second Affiliated Hospital of Shanxi Medical University), Yang Binbin (Department of Neurology, Second Affiliated Hospital of Central South University), Leng Yangming (Department of Otolaryngology-Head and Neck Surgery, Tongji Medical College, Huazhong University of Science and Technology), Du Yi (Department of Otolaryngology-Head and Neck Surgery, PLA General Hospital), Li Wen (Department of Neurology, Weifang People’s Hospital), Li Wenyang (Department of Otolaryngology, Eye, Ear, Nose, and Throat Hospital, Fudan University), Li Hongyan (Department of Neurology, Xinjiang Autonomous Region People’s Hospital), Li Mingxin (Department of Neurology, Qilu Hospital), Li Fei (Department of Otolaryngology-Head and Neck Surgery, Shanghai Changzheng Hospital, Naval Medical University), Li Xinyi (Department of Neurology, Shanxi Bethune Hospital), Yang Guoyuan (Department of Ophthalmology, West China Hospital, Sichuan University), Xiao Zufeng (Department of Neurology, First Affiliated Hospital of Gannan Medical University), Wu Mei (Department of Otolaryngology-Head and Neck Surgery, Xinjiang Uyghur Autonomous Region People’s Hospital), He Feng (Department of Neurology, Air Force Medical University, Xijing Hospital), He Li (Department of Neurology, West China Hospital, Sichuan University), Yu Feng (Department of Neurology, First Affiliated Hospital of University of Science and Technology of China [Anhui Provincial Hospital]), Wang Qin (Department of Otolaryngology-Head and Neck Surgery, Second Affiliated Hospital of Central South University), Zhang Xiaoli (Department of Otolaryngology-Head and Neck Surgery, Drum Tower Hospital, Nanjing Medical University), Zhang Yang (Department of Neurology, Drum Tower Hospital, Nanjing Medical University), Zhang Jin (Department of Otolaryngology, Boao Super Hospital), Zhang Ru (Department of Otolaryngology-Head and Neck Surgery, Shanghai Oriental Hospital), Zhang Li (Department of Otolaryngology, Inner Mongolia Medical University Hospital), Chen Xiaowan (Department of Otolaryngology-Head and Neck Surgery, First Hospital of Lanzhou University), Chen Xiaoyan (Department of Neurology, PLA General Hospital), Chen Gang (Dizziness Center, Shandong Provincial Hospital), Chen Weifeng (Department of Otolaryngology-Head and Neck Surgery, First Affiliated Hospital of Gannan Medical University), Chen Xi (Department of Otolaryngology-Head and Neck Surgery, Fujian Provincial People’s Hospital), Zheng Hong (Department of Otolaryngology-Head and Neck Surgery, West China Hospital, Sichuan University), Lin Ying (Department of Otolaryngology-Head and Neck Surgery, Air Force Medical University, Xijing Hospital), Zhou Renhong (Department of Otolaryngology-Head and Neck Surgery, Tongji Medical College, Huazhong University of Science and Technology), Luo Bin (Department of Psychiatry, First Affiliated Hospital of University of Science and Technology of China [Anhui Provincial Hospital]), Yue Wei (Department of Neurology, Huanhu Hospital, Tianjin), Zheng Hong (Department of Otolaryngology-Head and Neck Surgery, West China Hospital, Sichuan University), Zhao Yong (Department of Neurology, Third Hospital of Xi’an), Zhao Xiuli (Department of Neurology, First Affiliated Hospital of Harbin Medical University), Zhao Xue Ning (Dizziness Center, Shandong Provincial Hospital), Shi Tianming (Department of Neurology, Zhejiang Provincial People’s Hospital), Qin Qiong (Department of Otolaryngology, Yunnan Provincial Traditional Chinese Medicine Hospital), Suo Limin (Department of Otolaryngology-Head and Neck Surgery, Second Affiliated Hospital of Shanxi Medical University), Jia Hongbo (Air Force Medical Center), Xu Kaixu (Department of Otolaryngology-Head and Neck Surgery, Tianjin First Central Hospital), Xu Zhong (Department of Neurology, First Affiliated Hospital of Kunming Medical University), Xi Gangming (Department of Neurology, Shanghai Xuhui Central Hospital), Huang Rui (Department of Neurology, Shengjing Hospital of China Medical University), Chong Yi (Department of Neurology, Bao’an District People’s Hospital of Shenzhen), Liang Yanling (Department of Neurology, Third Affiliated Hospital of Guangzhou Medical University), Fu Xinxing (Department of Otolaryngology-Head and Neck Surgery, Beijing Tongren Hospital, Capital Medical University), Jiang Zidong (Department of Otolaryngology, Peking Union Medical College Hospital), Tong Linyan (Department of Neurology, Second Affiliated Hospital of Chongqing Medical University), Zeng Xiangli (Department of Otolaryngology-Head and Neck Surgery, Third Affiliated Hospital of Sun Yat-sen University), Cai Ruowei (Department of Neurology, Second Affiliated Hospital of Fujian Medical University), Fan Chunqiu (Department of Neurology, Xuanwu Hospital, Capital Medical University), Pan Yonghui (Department of Neurology, First Affiliated Hospital of Harbin Medical University), Xue Hui (Department of Neurology, Baotou Central Hospital), Ji Fei (Department of Otolaryngology-Head and Neck Surgery, First Medical Center of PLA General Hospital), Dai Qingqing (Department of Otolaryngology-Head and Neck Surgery, Second Affiliated Hospital of West China Hospital, Sichuan University), Ju Yi (Department of Neurology, Beijing Tiantan Hospital, Capital Medical University)

Clinical Journal of Otolaryngology-Head and Neck Surgery June 2023, Volume 37, Issue 6

Authors: Dizziness Specialty Committee of the Chinese Medical Education Association (Wang Wuqing, Qu Yongkang, Liu Bo, Liu Bo, Wu Ziming, Cao Xiaoping, Han Junliang as the main authors)

Expert Consensus on Diagnosis of Isolated Otolith Dysfunction

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