Discussion
The number of patients admitted to Norwegian hospitals for vestibular neuritis has increased substantially from 2011 to 2021 and at the end of this period was close to 15 per 100,000 inhabitants per year. This figure is still low in relation to the number of patients admitted for other vertiginous disorders.
There are very few comparable studies from other countries, but a study from Croatia (2) found an incidence of 15.5 per 100,000 inhabitants per year, which is almost the same as the incidence towards the end of the observation period in our study.
An incidence of vestibular neuritis of approximately 15 per 100,000 per year may still be an underestimate. Expertise in otoneurology is required to make the diagnosis. It is particularly important to be able to detect spontaneous nystagmus, as well as to correctly perform and interpret the head impulse test. Lack of appropriate examination equipment can lead to spontaneous nystagmus being overlooked. Patients with spontaneous nystagmus will also have nystagmus after the Dix-Hallpike manoeuvre and therefore may be incorrectly diagnosed with benign paroxysmal positional vertigo (BPPV). A variant of vestibular neuritis that only affects the inferior division of the vestibular nerve can be difficult to detect.
It is also possible that there may be underdiagnosis as a result of patients being treated outside of hospital. For several reasons, this probably applies to fewer patients than before. Firstly, our study shows that the number of patients admitted to hospital is increasing in all regional health authorities. New guidelines (3) specify that patients who experience sudden onset of persistent dizziness and nausea should be admitted to hospital as emergencies, including in order to detect and treat stroke. Furthermore, the symptoms of vestibular neuritis are often so intense – and so concerning both to the patient and general practitioner – that hospital admission is appropriate. This is both for diagnostic elucidation, which often includes diagnostic imaging, and for the initiation of required treatment, which in the acute phase often consists of providing patient information, quiet bedrest, antiemetics and optional systemic corticosteroids followed by early mobilisation and rehabilitation.
There is less likely to be any significant overdiagnosis of vestibular neuritis at the expense of more serious conditions such as stroke since access to MRI scanning is generally good at Norwegian hospitals. However, the diagnosis of vestibular neuritis does not require MRI because it is based on clinical criteria (1). In practice, the HINTS criteria (positive head impulse test, peripheral-type nystagmus and absence of skew deviation) are often used (4). It is unlikely that conditions such as Meniere's disease, labyrinthitis and vestibular schwannoma are often confused with vestibular neuritis because they are considerably rarer and usually cause unilateral hearing loss.
The diagnostic workup of vestibular neuritis at Norwegian hospitals has undergone improvements in the study period, and therefore it is likely that the latest figures are the best representation of the actual incidence in the population. Several hospitals have developed their own pathways for patients admitted to hospital with acute dizziness, and two of the country's largest hospitals have recently conducted a randomised controlled interventional trial on consecutive patients with vestibular neuritis (5), which required rigorous diagnostic procedures. For the past 20 years, Norway has had a centralised service for sharing expertise about vestibular disorders (Norwegian National Advisory Unit on Vestibular Disorders). Our study shows relatively small variations between the regional health authorities, even though two of the regions have been systematically above and below the national average, respectively (Figure 1).
The Norwegian Patient Registry collects data about all patients who are treated in the specialist health service, including primary diagnoses for hospital admissions. All organisations in the specialist health service that are wholly or partly publicly funded are required to report into the Norwegian Patient Registry. This mainly includes health trusts, private non-profit hospitals, private for-profit hospitals with tender agreements and specialists in private practice. One strength of our study is that the Norwegian Patient Registry has an extremely high level of completeness, and therefore it is reasonable to assume that we have included the vast majority of patients admitted to Norwegian hospitals for vestibular neuritis in the study period. Prevalence figures in our study can be regarded as an indirect estimate of incidence (new cases of the disorder) since vestibular neuritis usually only affects patients once in their life (6).
In this study, we found a considerable increase in the annual number of patients admitted to hospital for vestibular neuritis in the study period. This is likely to be a reflection of the increased hospitalisation rate and improvements in diagnostic workup more than an actual increase in the incidence of the disorder. A minority of patients admitted for vertiginous disorders had vestibular neuritis.