General characteristics of studies
Our initial trial for the literature search yielded 276 citations, 49 of which were duplicate studies. During screening, 209 studies were excluded based on the selection criteria (n = 183 after records title screening and n = 26 after abstract screening). Among the remaining 18 studies, 13 were excluded because of inappropriate study design (n = 9), no original data (n = 1), or because they were not written in English (n = 3). Therefore, five studies (n = 253) met the selection criteria and were included in the final analysis (Figure 1).
The major characteristics of the five articles 6, 14-17 are summarized in Table 1. The year of publication for the identified studies ranged from 1990 to 2018. The follow-up duration ranged from 1 to 12 months. The studies were conducted in Egypt, Germany, Israel, South Korea, and USA.
Three studies 14-16 compared the outcomes of the steroid treatment (ST) group with those of placebo (PL) or non-steroid treatment (NST) group. Three studies 6, 14-18 compared the outcomes among a combination of corticosteroids plus other treatments with those of other treatments alone. In two studies,6, 17 the outcomes of combined treatment of steroid treatment plus vestibular rehabilitation therapy (ST plus VRT) were compared to those of vestibular rehabilitation therapy alone (VRT only). One study 16 compared the outcomes of combined treatment of ST plus valacyclovir treatment (ST plus VA) with those of valacyclovir treatment alone (VA only). Since the number of studies was small for each comparison group, the results of each follow-up period and comparison group were considered and analyzed as separate studies.