Sudden sensorineural hearing loss: does a seasonal variation exist? A single-center retrospective study in Italy and a review of literature

BACKGROUND: Sudden sensorineural hearing loss (SSNHL) is a frightening symptom that often prompts an urgent or emergent visit to a healthcare provider. The aim of this study was to investigate whether a seasonal periodicity in the occurrence of SSNHL exists. METHODS: A retrospective study was conducted on cases of SSNHL referred across twenty years (23 September 2000 - 22 September 2020) at the local Ear-Nose-Throat (ENT) and Audiology Unit. For each case, date of onset, age, sex, presence of tinnitus or dizziness, involvement of other cranial nerves, and persistence of hearing loss after 4 weeks, were recorded. RESULTS: A total of 267 consecutive cases of SSNHL (49.4% males, mean age 55±15 years) were included. A seasonal periodicity was characterized by a not significant peak in summer and trough in winter (P=0.063). But comparison if cases happening in the warm and cold months showed a higher rate of observed/expected ratio (151 vs. 116 patients, P=0.035) during the warm months. These results were related to women (81 vs. 54, P=0.021), and older subjects (≥65 years) (58 vs. 38, P=0.033). CONCLUSIONS: SSNHL showed significant variations across the year, with highest frequency of onset during warm months, particularly in hot period, especially if ages ≥65 years and women. Environmental cues, relationship with possible disruption of biological rhythms and sleep disorders, and sex-oriented differences could be interesting pieces of the puzzle of the complex etiology of this clinical picture.