Progressive bilateral hearing loss (PBHL) is defined rather simply as the significant decline in the hearing of both ears at the same time.
PHBL comes in several different timing variants --rapid, and slow. Rapid (or subacute) over several months. Slow, over years. Autoimmune inner ear disease is an example of a subacute process. Age is an example of a slow process.
PBHL is not "Sudden" which defined as hearing loss occurring over roughly 48 hours. Sara et al (2014) reviewed "bilateral sudden sensorineural hearing loss" and found 103 reported cases in the world literature, most of which were "toxic, autoimmune, neoplastic or vascular".
Sudden bilateral hearing loss (SBHL) is related to the more common condition of "sudden hearing loss", or SHL, which generally is defined as being confined to one ear. Perhaps "SUHL" would be a better name than SHL. Sudden bilateral hearing loss occurs 20 times less commonly than sudden hearing loss in one ear (Oh et al, 2007). According to Chen and Young (2016), the prognosis is very poor for sudden bilateral hearing loss with a very high mortaility rate (44%) in 16 patients over 5 years.
PBHL is much more common than the unilateral hearing loss. For example, nearly 100% of the population eventually develops age related bilateral hearing loss.
PBHL also is divided up by location --including "conductive" (such as due to ear wax , otosclerosis, or fluid in the middle ear), "sensorineural" (inner ear or nerve), and "central" (brainstem and above). We will leave out the conductive causes below as they are nearly all just bilateral versions of unilateral disease. There are only a few rare exceptions due to bone diseases affecting the skull such as osteogenesis imperfecta, Pagets, Engelmann's disease, or fibrous dysplasia.
A list of the most common causes of PBHL include:
After one excludes the very common disorders above, what is left over is:
These are mostly processes that damage both ears or the nerves to the ears together.
In essence, PBHL is diagnosed by documenting an ongoing decline in hearing in both ears. This generally requires several audiograms.
Other than this, diagnosis of PBHL requires checking for a large number of individual causes, as outlined above.
Treatment of PBHL is generally specific to the cause. Cochlear implants are much more frequently used in this condition however.