TTS and PTS - Discordant or Concordant Twins?

The reduction in sensitivity level of ear on exposure to noise, described as shift in threshold of hearing can be temporary or permanent. This reduction shows high individual variation and occurs more on exposure to sounds  in the range of 2-6KHz. Temporary threshold shift (TTS)  and Permanent threshold shift (PTS) represent the most common hearing effect of acute and chronic high level acoustic stimulation (Quaranta et al, 1998). 

The interesting aspects concern the definition of duration of hearing loss (for TTS) and whether there is any relationship between the two entities. 

TTS is commonly defined as "rise in auditory threshold during short exposure to noise which normally disappears in 24 hours but may last as long as a week"

The fact is post exposure improvement of threshold following such exposure may continue for 30 days or longer and there may not be return to preexposure threshold level (I.e PTS may occur). 

The exact issue is there is no consensus as to how short or long one waits before pronouncing TTS a PTS. The exact point at which a TTS becomes a PTS is very difficult to identify.  Age, exposure duration, exposure to other ototoxicity factors, intensity of the impact noise are other factors determine PTS. 

The second issue is whether outcome of TTS studies can be grafted wholesale into prevention of PTS. 

For ethical reasons, studies on PTS focused on animals, while human studies concentrate on creating temporary hearing losses (TTS). Typically the latter assumes that PTS must always be preceded by TTS. This has been shown not be strictly true. TTS is simply not a predictor of PTS, and we do not currently have good predictor of TTS. 

The underlying molecular mechanisms are different for TTS (glutamate accumulation and tectorial membrane tip disconnection) and PTS (cell death related to apoptosis or necrosis). So TTS may not tell us much about PTS. 

Further Reading

1. Marshall Chasin. What does TTS tell us about PTS?  Available at hearing health matters.org/hear the music/2012/what-does-tts-tell-us-about-pts/ 
2. Scand Audiol Suppl 1998;48:75-86 
3. Otol Neurotol. 2016 Sep;37(8):e263-70. 

Focusing On A Third of The Story

Hearing loss is an invisible disability and like other disabilities often command the interest and attention of philanthropist and NGOs. The interesting aspect is the do-gooders always have genuine interest in helping out but are often unsure where to start. 

Take for example the Telco that desires to assist with hearing loss. In developing countries, the common approach  is to focus on hearing aids distribution. Most do it by getting hearing aids dispensers to assemble hearing impaired in the community and in the presence of TVs and the press, proceed to 'screen' and administer hearing aids in few cases. 

There is often no follow up to determine who benefits and who does not after such photo-shoots. Some even hand out hearing aids without ear moulds or ear inserts. 

Now the facts is hearing aids only benefit a third of the hearing impaired (arguably a quarter) and focusing solely on these is neglecting the remaining 3/4 - those who require middle ear surgery, those who require Cochlear implants, and those that cannot be helped by any currently known measures and likely to require educational and occupational rehabilitation. 

So while we appreciate efforts geared towards assisting the hearing impaired in our communities by donating hearing aids, please be mindful that there are countless others who would not benefit  from hearing aids and equally require assistance. As such please note you are only focusing on a third of the hearing loss story. 

Cat-Roommate Analogy for Tinnitus in Cases Coming for Ear Surgery

Tinnitus - the sensation of sound/noise in the ear or head is an age old symptom that continues to perplex sufferers and researchers alike. The interest in tinnitus stems not only from the fact that it is an annoyance to sufferers, but that there are as many types of tinnitus as there are theories about its origin. 

Tinnitus could be subjective (audible only to the sufferer) or objective (can be heard by the clinician as well as the sufferer), high or low pitch, regular or irregular noise, persistent or pulsatile and could result from organic and non-organic causes. Interestingly the noise could result from diseases affecting the external ear (ear wax, foreign body, growth, etc), the middle ear (plethora of these) as well as the inner ear (Meniere's disease, Vestibular schwanoma, etc) as well as diseases of the Eustachian tube, central nervous system and systemic diseases. 

Theories put forward to explain tinnitus focused on peripheral mechanisms (discordant damage to outer and inner hair cells, imbalance of afferent and efferent hair cells of the auditory pathway, etc), brain stem anomalies (inferior colliculus and dorsal cochlear nucleus hyperactivity / disinhibition, etc), and the cerebral cortex(auditory cortex / amygdala hyperactivities, etc) and other non-auditory mechanisms for generation of tinnitus. 

To tinnitus sufferer, the simple worry is 'Am I going crazy or is something terribly wrong with me or my head'?

To the clinician, the worry is 'Is this tinnitus of organic or non-organic source'? 'Is it of central or peripheral origins'? 'Is it associated with hearing loss'?

Now the interesting aspect is, with this plethora of possible etiologies, patients with tinnitus and middle ear diseases (like cholesteatoma and chronic suppurative otitis media) coming for ear surgeries (Tympanomastoidectomy, tympanoplasty) often ask the most interesting question: 'Will this noise disappear after my ear surgery'? 

After a decade of middle ear surgery, I finally found the most interesting analogy as response to that scary question. It goes like this:

Imagine there are 3 of us living in a house - you (patient), myself (the clinician) and a cat. Now imagine the 2 of us were seated in the living room and a noise was headed continuously from the bedroom, with the cat nowhere in site! 

The interesting initial  assumption  is "it is that stupid cat'. 

Now there is only the one way to verify that assumption: Go into the bedroom and look for the cat. Now, this is where it gets so interesting, finding a cat in the room does not CONFIRM it is the source of the sound/noise. What the modern scientific medicine taught is that we remove the cat from the room, close the door and go back to the living room to listen again. It is the absence of the noise/sound after that, that CONFIRMS 'It is the cat'. Persistence of the sound after that means we need to look for other source(s) of the sound. 

This "Cat Roommate" analogy has assisted me in putting succinctly the reality regarding expectations from middle ear surgery in patients with background tinnitus. Perhaps you may find it useful for your cases too. 

Further Reading

1. Theories of generation and management of tinnitus. https://www.mayo.edu/mayo-edu-docs/mayo-clinic-audiology-conference-documents/handouts-new-theories-on-the-generation-and-management-of-tinnitus.pdf 

2. Tinnitus- Current neuroscience research and theories. http://www.hearingloss.org/sites/default/files/docs/LeaverAM_.pdf