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.