Introduction
Sudden sensorineural hearing loss (SSNHL) is a rare emergency. Despite having been described first by De Kleyn in 1944 (1), SSNHL continues to remain one of the most challenging and controversial conditions in modern otology. It is defined as a hearing loss developing within three days, and confirmed by audiometric testing demonstrating a decrease of at least 30 decibels in hearing thresholds across three consecutive frequencies (comparing the affected to the opposite ear) (2). In practice, the diagnosis is often made with lesser degrees of hearing loss.
Insurance data from the USA suggests that SSNHL affects 27 per 100,000 individuals per annum (3). SSNHL is a disorder of uncertain aetiology, with only half of those affected recovering hearing (4) and many reporting persistent disability (5). It is often treated with systemic or local steroids, given within 14 days of symptom onset.
It is believed that SSNHL can result from autoimmune, metabolic, neurological, otological or vascular disease, infections, neoplasms, ototoxic agents, or trauma (4). However, in the majority of cases the cause is not evident. A number of ideas have been proposed to explain idiopathic SSNHL, and evidence from clinical, pathological, radiological and animal studies suggest that exposure to a virus (or one of a number of viruses) is the most likely aetiology in many idiopathic cases (4).
Here we present the first report of temporospatial clustering of three cases of idiopathic SSNHL, all presenting with unilateral low frequency loss. Such clustering suggests an environmental trigger to aetiology, consistent with a transmissible agent such as a virus.