Are hearing and olfaction disorders more common in older patients with diabetes? Are hearing loss and olfactive disfunction a risk factor for progression of functional decline and disability?| JOURNAL OF GERONTOLOGY AND GERIATRICS

1. RECOMMENDATIONS

1. All geriatric DM patients should undergo audiological and audiometric examinations, followed by annual/twice-yearly check-ups.
2. More attention should be given to auditory rehabilitation programs, with prescription of appropriate hearing aids, to improve quality of life and cognitive functioning.
3. If concerns arise about a patient’s hearing status, they should undergo pure tone audiometry, but also speech audiometry (including a measurement of speech recognition thresholds, preferably in both quiet and noise), which tries to reproduce daily life condition and to assess actual speech comprehension in a daily life-like condition.
4. All geriatric DM patients should undergo screening to evaluate olfaction and taste functioning, with regular follow-ups to assess any potential impact on nutritional status.

2. STRENGTH OF THE RECOMMENDATIONS

The quality of the evidence is moderate. Recommendations are supported by published evidence and best practice (supported by expert opinion).

3. SUPPORTING EVIDENCE

See appendix.

4. AREAS OF UNCERTAINTY AND FUTURE PERSPECTIVES

Many studies on hearing performance have been conducted on middle-aged T2DM patients, but there is less clarity in geriatric patients, possibly because they start to develop also age-related hearing loss. Further studies are needed to clarify whether decline in olfaction and taste is a result of ongoing neurodegenerative disease or whether it directly contributes to causing or accelerating cognitive decline.

APPENDIX

Hearing loss is considered to be the second most frequent disorder in older people, and it is present in a third of people aged 65 or more, and almost 50% of those over 75 years ¹. There is growing evidence that hearing loss is associated in some way to cognitive decline. The proposed mechanisms behind this association include direct neurodegenerative damage to auditory and central nervous systems, indirect associations through social isolation, depression, and reduced sensory stimulation, and accelerated brain atrophy cause by the recruitment of additional cognitive resources to understand language and other auditory stimuli ².

The association between DM and hearing loss is complex: most available studies show an association between auditory deficits and DM ³. This association is widely accepted for middle-aged patients with DM, with a marked increase for high-frequency sounds. Some authors have also reported a higher risk of developing incident hearing loss in DM patients ^3,4 and there is evidence that this is associated with HbA1c values ⁴, suggesting a potential pathogenic role of glycemic control.

There is less clarity about this association in older people ⁵, possibly because they start to develop age-related hearing loss. Therefore, quantitative assessments of auditory thresholds are necessary to accurately assess the potential effect of T2DM on hearing loss in the elderly. Geriatric DM patients seem to have faster age-related hearing loss than non-diabetic patients ⁶ and, in general, longer DM disease duration is associated with auditory deterioration ⁷. This is particularly important among older people with a long history of DM; in these patients age-related hearing loss and DM may act in synergy to accelerate and exacerbate hearing loss.

Histopathological studies on animal models and patients have revealed microangiopathic changes in the capillaries of the stria vascularis in the cochlea (particularly in the basal curve, which is responsible for high frequency hearing) ⁸ and damage to external hearing cells ⁹; features which are also present in age-related hearing loss ^10,11. Some authors also report that hearing loss is accelerated in people with poorer initial hearing thresholds ¹², while other authors report the opposite ¹³, although they show only a small decrease in the progression of hearing loss in patients with poorer initial thresholds.

Several studies have highlighted an association between olfactory hypofunction and DM ¹⁴, possibly in relation to antidiabetic treatment ¹⁵ and insulin-resistance ¹⁶, but there is little data available for geriatric DM patients. Conversely, there is less clarity about taste: some authors also report that this sensory function is compromised ¹⁷, while others have not found any significant association ¹⁸. Both taste and olfaction contribute to the perception of complex flavors and, interestingly, olfaction and taste functioning appears to be related to eating behaviour in patients with DM; impairment in olfaction and taste can lead to a dysregulation of food intake in DM patients ^18,19, leading to weight increase and obesity, which can complicate the disease and the patient’s general clinical situation.

There is no specific data on taste and olfaction in geriatric DM patients, but these senses are often compromised in older people during the early stages of neurodegenerative diseases like Alzheimer’s or Parkinsonism ²⁰. Further studies are needed to clarify whether decline in olfaction and taste is a result of ongoing neurodegenerative diseases or whether it directly contributes to causing or accelerating cognitive decline.

Acknowledgement

None.

Ethical consideration

Studies included raised no significant ethical issues.

Funding

None.

Conflict of interest

The Author declares no conflict of interest.

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