9Sudden & autoimmune hearing loss
Most causes in this chapter act slowly or are fixed from birth. Two do not, and they are united by the fact that how fast the hearing changes is itself the diagnosis — and the chance to intervene. Sudden sensorineural hearing loss drops over hours to days and is a true otologic emergency, because prompt steroids offer the best hope of recovery. Autoimmune inner-ear disease climbs over weeks to months, often in both ears and fluctuating, and is one of the very few sensorineural losses that responds to immunosuppression. Both are mistakes to miss: the first because the window is short, the second because it is one of the rare treatable causes — and occasionally a maker of bilateral implant candidates.
TTempo as a clue
Among the causes of sensorineural loss, rate of change is a powerful diagnostic signal. A loss that appears over hours to days points to a vascular, viral or idiopathic sudden event; a loss that progresses over weeks to months, especially bilaterally and with fluctuation, raises the possibility of an autoimmune process. Both demand urgency precisely because both may be treatable if caught in time.
CSudden SNHL — an emergency
Sudden sensorineural hearing loss is conventionally defined as a drop of at least 30 dB across three contiguous frequencies within 72 hours, usually unilateral. Most cases are idiopathic, though some reflect viral, vascular or (rarely) retrocochlear causes — which is why an asymmetric sudden loss warrants MRI to exclude a vestibular schwannoma. The clinical imperative is speed: corticosteroids (oral or intratympanic) within the first two weeks give the best chance of recovery, so a sudden loss must never be dismissed as wax or a cold.[2019]
CAutoimmune inner-ear disease
Autoimmune (immune-mediated) inner-ear disease, first described by McCabe, is a rapidly progressive, bilateral, often fluctuating sensorineural loss developing over weeks to months, sometimes with vestibular symptoms and sometimes alongside systemic autoimmune disease. Its defining and clinically vital feature is responsiveness to steroids and other immunosuppression — making it one of the few sensorineural losses that can be halted or reversed medically. Recognising it is the whole game.[1979]
CWhen they reach the implant
Most sudden losses either recover or remain unilateral, and a persisting single-sided deafness is itself now an implant indication. Autoimmune disease, by contrast, can progress to bilateral severe-to-profound loss despite treatment, producing an implant candidate — and because the process burns out the cochlea relatively acutely, the spiral ganglion is often reasonably preserved, so outcomes can be good. The lesson these two share with the rest of the chapter is that the cause carries a treatment window: miss it, and a recoverable loss becomes a permanent one.
What is the key diagnosis to consider, and why is it urgent?
How is sudden sensorineural hearing loss conventionally defined, and why does it matter?
What makes autoimmune (immune-mediated) inner-ear disease so important to recognise?