聴力低下がアルツハイマー型認知症者の認知機能，言語機能に及ぼす影響

Effect of hearing loss on cognitive and language functions in patients with Alzheimer's Disease

　アルツハイマー型認知症者52例を対象に，気導純音聴力検査，MMSE，言語検査を施行した．平均聴力レベルとMMSE総点，言語検査総点の相関係数は，それぞれr＝－.13，.28で相関はみられず，聴力低下は認知機能，言語機能全体に影響を及ぼすものではないと考えられた．聴覚障害重症度により対象を聴覚障害群，非聴覚障害群の2群に分け分析を行った結果，聴覚障害群は非聴覚障害群に比し，MMSE下位項目「遅延再生」が有意に低得点，言語検査下位項目「漢字書字」「仮名書字」が有意に高得点であった．下位項目の分析から聴力低下はワーキングメモリーを消耗させる可能性，環境的な要因により書字能力が良好となる可能性の2点が示唆された．また，アルツハイマー型認知症者の聴覚障害罹患率は，96.1％と高いにもかかわらず，補聴器使用者は1例もおらず，今後，認知症者の補聴器装用が可能な条件を検討する必要があると思われた．

　We conducted a pure-tone air conduction hearing test and administered the MMSE and the Language Function Test to 52 patients with Alzhaimer's Disease(AD). Pure Tone Average(PTA) did not correlate with either the total score of MMSE(r＝－.13) or Language Function Test(r＝.28). We therefore suggest that hearing loss has no general effect on overall cognitive and language functions of AD patients. Next, we divided the patients into the Hearing Impaired(PTA≧41dBHL) and Hearing Unimpaired(PTA≦40dBHL) groups and performed a non-paired t-test to clarify the difference between the two groups. Significant differences were found for delayed recall(0.9±1.0, 2.0±0.6), kanji writing(1.0±0.8, 0.2±0.4) and kana writing(2.6±1.0, 1.5±1.6). We think that hearing loss has an adverse effect on working memory but a positive effect on maintaining writing ability. The prevalence of hearing loss among the subjects was 96.1%, but no subject wore a hearing aid. We think it is important to investigate conditions that enable AD patients to wear hearing aids.