[Clinical reclassification of low-frequency type of sudden sensorineural hearing loss]

Objective:To further classify refractory low-frequency sudden sensorineural hearing loss（SSNHL） and investigate the clinical characteristics and prognostic differences among various subtypes. Methods:A retrospective analysis was conducted on 208 patients with refractory low-frequency SSNHL who were hospitalized in Department of Audiology and Vestibular Medicine, Senior Department of Otolaryngology Head and Neck Surgery, Sixth Medical Center of the PLA General Hospital after failing conventional outpatient treatment. Based on clinical manifestations, patients were classified into four subtypes: migraine-associated type, hypotension or low intracranial pressure type, endolymphatic hydrops type, and other types. The clinical characteristics and prognostic outcomes were compared among the groups. Results:Significant differences were observed among the four groups in terms of sex distribution, affected ear side, accompanying symptoms（tinnitus, aural fullness, vertigo, or dizziness）, and progression to Meniere's disease（all P<0.05）. Pairwise comparisons revealed that the proportion of females in the migraine-associated group was significantly higher than that in the endolymphatic hydrops and other groups（all P<0.05）. The left ear was more frequently affected in the endolymphatic hydrops group than in the hypotension or low intracranial pressure group（P=0.027）. Tinnitus was significantly more common in the endolymphatic hydrops and other groups than in the hypotension or low intracranial pressure group（all P<0.05）. The migraine-associated group exhibited significantly higher rates of aural fullness, vertigo or dizziness, and progression to Meniere's disease compared to the other group （all P<0.05）. Regarding prognosis, the cure rates in the migraine-associated and hypotension or low intracranial pressure groups were 61.9% and 57.8%, respectively, significantly higher than those in the endolymphatic hydrops（11.8%） and other groups（27.0%）（all P<0.05）. The recurrence rate in the migraine-associated group was 52.4%, significantly higher than that in the other group（21.4%）（P<0.05）. The migraine-associated group demonstrated a significantly higher incidence of high-frequency hearing loss compared to the other groups（all P<0.05）. Long-term follow-up revealed that this subtype was associated with more frequent hearing fluctuations, while hydrops and circulatory types retained potential for hearing recovery. Conclusion:Significant differences in clinical characteristics and prognosis exist among subtypes of refractory low-frequency SSNHL.The migraine-associated subtype is prone to fluctuating or recurrent hearing loss and has a higher risk of high-frequency hearing impairment. The hypotension or low intracranial pressure subtype has a relatively favorable prognosis, with a lower incidence of cochlear symptoms such as tinnitus and aural fullness. The endolymphatic hydrops subtype is associated with a poorer prognosis, although hearing may improve during long-term follow-up.