Hearing outcomes
All groups of patients with UMD exhibited a mean tonal threshold corresponding to moderate hearing loss, with a greater degree of low-frequency hearing loss at the beginning of the disease. These thresholds evolved to a more severe degree of hearing loss by the end of follow-up.
Significant differences were observed when the extent of hearing loss was considered in association with the different clinical models (Table 2).
4.DISCUSSION
Evolution of vertigo episodes and clinical models
Understanding the general evolution of vertigo episodes and taking into account our clinical experience and the individual revision of each case, we observed that the evolution of vertigo episodes differed considerably between cases during the first 10 years of the disease. We decided to define a series of criteria according to which the whole cohort of patients could be assigned to different subgroups.
We defined a series of subgroups based on the evolution and behaviour of vertigo episodes, although there are many ways of grouping the clinical variations typical of MD (6–8).
In our view, the most relevant work in this regard is that in which five subgroups of patients were defined (7): classic MD, delayed MD, familial MD, MD associated with migraine and MD associated with autoimmune disorders. In our models, familial association and a history of autoimmune diseases are not taken into account, although some hypothetical associations and comparisons could be made with these groups. Our model number 2 was that in which patients most frequently also suffered from migraine and that in which there was an earlier disease onset, as previously reported for the subgroup of patients with MD associated with migraine. Model number 3 had the highest proportion of patients that suffered a Tumarkin crisis and no patient with migraines, and it was the model in which the patients experienced the largest number of vertigo episodes, as reported previously(7), as the subgroup of patients with MD associated with autoimmune diseases.
Accordingly, in different studies in this field groups of patients have been classified based on specific criteria(6,7). However, as they share common features, it would appear that there are different forms of MD that can be distinguished on the basis of the criteria used in these studies.