A news article, published in The Daily Mail last Tuesday, claimed that a group of American scientists had ‘cured’ tinnitus in mice and that this breakthrough could potentially ‘pave the way’ for a human cure.[i]
What is Tinnitus?
According to the British Tinnitus Association:
‘Tinnitus is the term for the sensation of hearing a sound in the absence of any external sound. Symptoms of tinnitus are you may hear different types of sound, for example, ringing, whooshing or humming or buzzing in the ear. These can be continuous or they can come and go. The tinnitus might seem like it’s in one ear or both, in the middle of the head or even be difficult to pinpoint’.
Tinnitus is a subjective condition (i.e. there is no method of assessment), which is commonly alleged in conjunction with noise-induced hearing loss (NIHL) in industrial disease claimant pleadings.
In spite of subjectivity, the impact of increasing tinnitus severity on the value of occupational deafness claims is significant – see Chapter 5(B)(d) of the JC Guidelines (14th Edition) below:
Nevertheless, the majority of people will suffer from mild and moderate grading of tinnitus; severe tinnitus is uncommon.
What Causes Tinnitus?
Tinnitus is associated with hearing loss, both conductive and sensorineural.
Sensorineural hearing loss, typically caused by the ageing process (Presbycusis) and prolonged exposure to excessive levels of noise, damages hair cells within the inner ear (the cochlea and/or auditory nerve).
Conductive hearing loss, typically caused by a build-up of wax, obstructs or damages the outer and/or middle ear.
(Source: Wikimedia Commons)
Our hearing relies on vibrations reaching the cochlea. Vibrations ripple waves of cochlear fluid, which oscillate hair cells and open up microscopic stereocilia. Chemicals enter theses openings and the auditory (vestibulocochlear) nerve carries an electrical signal to the brain, which is converted into a sound that we recognise and understand.[ii]
(Source: Wikimedia Commons)
Put simply, if there is obstruction/damage to the inner, middle, or outer ear, which prevents the transmission of information to the brainstem, then the brain will actively ‘seek out’ signals from working parts of the cochlea. These signals may become ‘over-represented’ and this over-representation is what we perceive as tinnitus.[iii]
Other factors associated with tinnitus include:
- Hidden hearing loss;
- Acoustic shock;
- Meniere’s disease;
- Paget’s disease;
- Perforation of the eardrum;
- Multiple Sclerosis;
- Ototoxic (aminoglycoside, cytotoxic, loop diuretic) drug use;
- Common (anti-malarial, aspirin, anti-hypersensitive, antihistamine, anti-inflammatory) drug use;
- Solvent, drug and alcohol misuse;
- Head injury;
- Stress; and
A New Tinnitus Cure?
Until now, tinnitus has been deemed incurable, primarily because the mechanisms underlying hearing loss-related pathologies are poorly understood.
However, the latest academic paper, referred to in last week’s Daily Mail article and published in the PLoS Biology journal, claims to have discovered a working noise-induced tinnitus gene therapy.[iv]
Wang et al (2019) exposed a group of rodent test subjects to loud noise for 2 hours, inducing NIHL. They examined the effects and identified that the immune system’s natural response to hearing loss was for the auditory pathway to become inflamed. Specifically, the University of Arizona researchers identified 2 defining features of inflammation (‘elevated levels of molecules called proinflammatory cytokines and the activation of non-neuronal cells called microglia’) in the primary auditory cortex (sound-processing region).
Having targeted neuro-inflammation as a potential cause of tinnitus, the researchers attempted to block a molecule that disrupts communication between neurons, called TNF-A (tumor necrosis factor alpha).
In doing so, study co-author and neuroscientist, Dr Shaowen Bao, explained that:
‘... pharmacologically blocking its [TNF-A] expression prevented neuro-inflammation and ameliorated the behaviour associated with tinnitus in mice with noise induced hearing loss’.
Although it has been proposed that successful gene therapy in animals may be replicated in humans, the potential adverse effects must be thoroughly investigated before human trials can commence.
[i] ‘Drug to reduce brain inflammation CURED tinnitus in mice - paving the way towards a pill for humans’ (18 June 2019 Daily Mail) <https://www.dailymail.co.uk/health/article-7155337/Drug-reduce-brain-inflammation-CURED-tinnitus-mice-paving-way-pill-humans.html> accessed 26 June 2019.
[iii] ‘Tinnitus’ (NHS Direct Wales) <https://www.nhsdirect.wales.nhs.uk/Encyclopaedia/t/article/tinnitus/> accessed 26 June 2019.
[iv] Wang W et al., Neuroinflammation mediates noise-induced synaptic imbalance and tinnitus in rodent models. PLoS Biol. 2019 Jun 18;17(6):e3000307. <https://journals.plos.org/plosbiology/article/file?id=10.1371/journal.pbio.3000307&type=printable> accessed 26 June 2019.