Changes in the Auditory Association Cortex in Dementing Illnesses.

OBJECTIVE: To evaluate the relationship between degree of cognitive impairment and gray-matter density changes in the auditory cortex. STUDY DESIGN: Retrospective case-control. PATIENTS: Six hundred sixty-three patients of a tertiary referral center cognitive disorders clinic. INTERVENTION: Magnetic resonance imaging. MAIN OUTCOME MEASURES: Ratios of gray matter density of the primary auditory cortex (A1) to whole brain and auditory association cortex (AAC) to whole brain in patients with Alzheimer's disease (AD) compared with mild cognitive impairment (MCI) and patients with a mini-mental state exam (MMSE) scores ≤25 versus >25. RESULTS: After multivariate analysis, a statistically significant difference between AAC to brain ratios for patients with a MMSE ≤25 (n = 325) compared with >25 (n = 269) was found, with values -0.03 (95% CI -0.04 to -0.02, p < 0.0001) on the left and -0.04 (95% CI -0.06 to -0.03, p < 0.0001) on the right. The adjusted average difference of left and right AAC to brain ratios between AD patients (n = 218) compared with MCI patients (n = 121) was also statistically significant, at -0.03 (95% CI -0.05 to -0.01, p = 0.004) and -0.05 (95% CI -0.07 to -0.03, p < 0.0001), respectively. There was no statistically significant difference in the left or right A1 to brain ratios between the MMSE groups or between the AD and MCI groups. CONCLUSIONS: The AAC for patients with MMSE ≤25 and for those with AD shows decreased gray matter density when compared with patients with better cognitive function. No difference was detected in A1, raising the possibility that patients may have intact neural hearing, but impaired ability to interpret sounds.

Hearing loss as a risk factor for dementia: A systematic review.

OBJECTIVES: To review evidence of hearing loss as a risk factor for dementia. Data Sources: PubMed Review methods: A systematic review was conducted using the PubMed database using the search terms (hearing loss OR presbycusis) AND (dementia OR cognitive decline). Initially, 488 articles were obtained. Only those studies evaluating an association between hearing loss and incident dementia or cognitive decline were included in the analysis. This resulted in 17 articles which were thoroughly evaluated with consideration for study design, method for determining hearing loss and cognitive status, relevant covariates and confounding factors, and key findings. RESULTS: All of the 17 articles meeting inclusion criteria indicate that hearing loss is associated with dementia or cognitive decline. The methods used among the studies for ascertaining hearing loss and dementia were notably varied. For hearing loss, peripheral auditory function was tested far more than central auditory function. For peripheral audition, pure tone audiometry was the most commonly reported method for defining hearing loss. Only a few studies measured central auditory function by using the Synthetic Sentence Identification with Ipsilateral Competing Message test (SSI-ICM) and the Staggered Spondaic Word Test (SSW). Dementia was most often defined using the Mini Mental State Exam (MMSE). However, many studies used extensive batteries of tests to define cognitive status, often including a neuropsychologist. Confounding variables such as cardiovascular risk factors were measured in 17 studies and family history of dementia was only evaluated in 1 study. Overall, the methods used by studies to ascertain hearing loss, cognitive status and other variables are valid, making their evaluation appear reliable. CONCLUSION: While each of the studies included in this study utilized slightly different methods for evaluating participants, each of them demonstrated that hearing loss is associated with higher incidence of dementia in older adults. LEVEL OF EVIDENCE: Level V, systematic review.