Epidemiology of post-earthquake dizziness in Kumamoto prefecture

Past major earthquakes have been associated with an increase in the prevalence of vertigo or dizziness; the 2016 Kumamoto earthquakes on April 14 and 16 (JST, moment magnitude=7.0, Shindo 7 Japanese seismic scale) and the large numbers of aftershocks were no exception. Several months after the initial earthquake, significant outbreaks of vertigo or dizziness occurred over a large area surrounding the epicenter of the earthquake. However, it is unclear why major earthquakes cause these symptoms. After the major earthquake in Kumamoto, we conducted a questionnaire and medical records survey to investigate post-earthquake dizziness (PED). This survey covered a total of 575 subjects who complained of exacerbation of vertigo or dizziness after the earthquake and visited the hospital for follow-up before the scheduled dates. Our results showed that the number of patients with vertigo or dizziness who visited the hospital increased after the earthquake, and peaked between 2 and 4 weeks after the earthquake. The timing of onset of vestibular disorders varied according to the underlying disease. This study also suggested that earthquake-related psychological stress or stress resulting from earthquake evacuation could cause the onset of some vestibular disorders. We speculated that PED could be caused by stimulation of the vestibular and visual systems and bathyesthesia, psychological stress, potential effects of autonomic stress on the equilibrium function, and/or sensory mismatch. Our study could contribute to establishing PED as a new concept in the area of vestibular disorders.