2.Body of text
1.INTRODUCTION
After the first episode, episodes of vertigo are recurrent in MD. However, how the behaviour of the disease evolves as a function of the number of vertigo episodes it still not absolutely clear. From the first year of the disease, there is a gradual decrease in the number of vertigo episodes over the first eight years of the disease, which is followed by a subsequent stabilization, and then by a mild and progressive decrease in the following 10 years (1). However, there are reports of an increase in the number of seizures/year in those patients who have experienced episodes for more than 10-15 years (2,3). In contrast, MD is also associated with periods of remission in which the individual does not experience any episode of vertigo, with a variable duration between the episodes of vertigo (4,5) that may ultimately lead to a complete cessation of the episodes of vertigo. We do not know how or when these periods of remission arise, yet it has been proposed that 70% of patients who do not have episodes of vertigo for one year will not experience any episode during the following year (1).
Although the course of the vertigo episodes in MD is well-defined for the general population of MD patients, it does not accommodate the wide clinical variability presented by each individual patient. In addition, there is considerable heterogeneity regarding the evaluation of these episodes of vertigo, their duration and intensity. The heterogeneity among patients with MD, not only in the course of vertigo episodes but in several other aspects of the disease, makes us think that there are different subtypes of MD. In recent years, new studies have emerged that attempt to explain this variation or the heterogeneous behaviour of the disease, attempting to identify clinical subgroups to help explain the different forms of the disease (6–8).
2. OBJECTIVES
After analyzing the course of the disease in a very large series of patients who have been followed since the onset of the disease, we found that the evolution of the symptoms in patients differed based on the annual number of vertigo episodes in the first 10 years of the disease. Therefore, we wanted to assess the possible existence of “subtypes” of MD based on the frequency of vertigo episodes in the initial years of the disease, and help to define the natural evolution of unilateral MD (uMD).
3. MATERIALS AND METHODS
A longitudinal descriptive study was carried out on patients from two referral centres with UMD. The patients’ data was collected and stored from 1977 to 2018, after which the data collected was processed and analysed. All the patients data were revised to confirm that they met updated criteria for complete MD.
At their first visit to each of the centers, the patients were advised to consult the Otorhinolaryngology (ENT) specialist every six months. At the first and subsequent visits, different variables were registered: clinical - onset of each symptom, date of the first visit, follow-up time, number of vertigo episodes in the last 6 months, type and date of the different surgical interventions undertaken, associated diseases, presence of Tumarkin crisis; audiometric - hearing parameters according to liminal pure tone audiometry at frequencies of 250, 500, 1,000, 2,000 and 4,000 Hz.
After recording the different variables, we analysed the evolution of the vertigo episodes in each patient during the period in which they were followed. This period was defined as the time elapsed between the first and the last visit, or in the case of those who underwent a surgical intervention, the date of this intervention was taken as the end of the follow-up for our study. We consider the following as surgical procedures that can modify the natural evolution of the disease: chemical labyrinthectomy, surgical labyrinthectomy, endolymphatic sac decompression, vestibular neurectomy, or cochlear implantation.
Many of the patients came to seek care a few months or years after the onset of disease symptoms. Thus, we could not precisely define the exact evolution of their disease before they were attended at the care centers. For this reason, a subgroup of patients who had been followed from the onset of the disease was defined. This subgroup included those patients in whom the time elapsed from the onset of the first symptom and the first visit to the ENT service was ≤365 days.
In this group, for which we have reliable information on the evolution of the disease, the number of annual vertigo episodes was revised individually and accordingly, 3 clinical evolutionary models were defined according to the evolutionary behaviour of the episodes in the first 10 years of the disease.
All patients gave their written consent that they wanted to participate in this work.