But it looks like hearing aids help, researchers say.
Hearing loss increases the chances of developing Parkinson’s disease down the track, but getting a hearing aid within two years of diagnosis attenuates that risk.
Those are the findings of a recent study of almost 3.6 million US veterans published in JAMA this month.
And they are not a surprise, Professor David Finkelstein, head of the Parkinson’s Disease Laboratory at the Florey Institute in Melbourne, told TMR.
“The concept of Parkinson’s has changed dramatically over the last five years,” said Professor Finkelstein, who was not involved in this research. “Now we know that there’s neuronal changes everywhere in the body. It’s a whole-body disease. It’s systemic. It affects gut, skin, sweat, eyes, saliva, brain as well, and it is no surprise that another neuronal group is affected.”
The very large US study, using the country’s military veterans database, showed that having hearing loss of any severity was associated with a 26% higher chance of developing Parkinson’s at least 10 years after testing than if there was no hearing loss.
But wearing a hearing aid reduced the cumulative increase in Parkinson’s cases per 10,000 people with hearing loss by 11.7 at five years, 21.6 at 10 years and 22.6 at 20 years.
“Given that hearing loss, even that of mild severity, synergises with known prodromal disorders and leads to a greater-than-additive risk of incident PD, hearing screening should be enforced at the primary care level even in the absence of a patient expressing hearing concerns,” the authors of the study write.
Sensory declines could suggest that neural pathways have been damaged by neurodegeneration, and hearing loss is one of the biggest modifiable risk factors for Alzheimer’s, which overlaps with Parkinson’s, the authors say.
“It may be the most important modifiable risk factor for dementia in midlife and could prove to be the same for PD.”
The participants in this study were all aged 40 and over and had an audiogram conducted from 2019-22. They were 96% male, mostly white, with a mean age of 67. “While the proportions of individuals from underrepresented racial and ethnic minority groups are small, in our cohort they still represent a large group in absolute terms,” the authors note.
About 79% had hearing loss – 30% mild, 29% moderate, 16% moderate to severe, and 4% severe to profound. The researchers took into account age, gender, smoking status, race, ethnicity and frailty when adjusting results.
After a mean follow-up of 7.6 years, 0.7% of those with any hearing loss developed Parkinson’s, while 0.3% of those with undamaged hearing did so. The association deepened with the severity of hearing loss.
People with mild hearing loss had an additional 6.1 cases of Parkinson’s per 10,000 people at five years, increasing to 9.1 at 15 years, compared to those without hearing loss. Moderate hearing loss was associated with an additional 15.8 cases at 10 years and 20.4 at 15 years; moderate to severe with 16.2 additional cases at 10 years and 22.3 at 15 years; and severe to profound hearing loss with 12.1 additional cases at 10 years and 20.5 at 15 years.
The mechanism by which hearing loss increases Parkinson’s incidence is unknown, the authors say: it may cause neurodegeneration, increasing tau neurofibrillary degeneration and neocortical Lewy bodies and accelerating brain volume atrophy, or maybe it does so indirectly by reducing social interaction, increasing depression or cognitive load.
Beyond the effect of hearing loss alone, the study found that its combination with other early signs of Parkinson’s – constipation, depression, anxiety, erectile dysfunction, global cognitive deficit, rapid eye movement sleep behaviour disorder (RBD), hypersomnia, orthostatic hypotension, anosmia, and urinary dysfunction – resulted in a great number of expected cases of Parkinson’s than the sum of the parts.
For instance, at 20 years, in people with a history of a prodromal disorder, there were 23.5 cases of Parkinson’s per 10,000 people. In people with mild hearing loss only, there were six per 10,000. In people with a combination, there were 36 cases of Parkinson’s per 10,000. Moderate hearing loss was associated with 14.8 cases per 10,000; the combination, 52.5. And severe to profound hearing loss alone was associated with 15.6 cases per 10,000 people, versus 59.4 for those with additional prodromal symptoms.
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Professor Finkelstein’s lab in Melbourne is working on therapies for people experiencing early symptoms of Parkinson’s.
Together, symptoms like loss of smell and hearing, as well as gut disturbances and RBD could be early signs of Parkinson’s, what’s called prodromal Parkinson’s, “and this is the hot news in the world of Parkinson’s”, said Professor Finkelstein.
“We’re trying to develop therapies to be used in people with hearing loss, loss of sense of smell, RBD and gut disturbances. If we have that cluster, it says you’ve got prodromal disease, and so that’s where we think we can actually prevent the onset of the clinical symptoms of movement. That’s our goal, to prevent Parkinson’s,” he said.
“GPs are actually on the front line, always, because they are going to be involved in detecting these seemingly benign symptoms.”
And the earlier it’s spotted, the better.
“At the time of diagnosis of Parkinson’s, more than 50% of the cells are lost from many parts of the brain, not just one. So if you can get to these cells before they die, before you get to the symptoms, you’ve actually got a way of modifying the course of the disease,” said Professor Finkelstein.
Fortunately, there was very good emerging evidence that controlling blood pressure, exercising and eating a Mediterranean diet might reduce the rate of progression for Parkinson’s, he said.
Meanwhile, the number of diagnoses had doubled in the last 15 years, and was expected to double again because of covid, influenza, and other environmental factors such as plastics.
“There’s been a long association with viruses in in Parkinson’s and we’re starting to anecdotally hear from neurologists and GPs that they’re seeing people who have had long covid with a Parkinsonism,” he said.
People living with Parkinson’s, and their carers, families and clinicians can access support, information and training through the Fight Parkinson’s organisation, which provides specific training for clinicians and a resource especially for GPs.
