認知症の症状と医学的対応

Dementing disorders: Symptoms and medical treatment

　記憶の種類を挙げ，認知症で障害されるのが出来事の記憶か知識(意味記憶)であることを述べた．つぎに，認知症の原因として多い3つの変性疾患に関して，病態，障害されやすい脳部位，そのために生じる症状，薬物療法，周囲の接し方についてそれぞれ簡単に解説した．Alzheimer病は，海馬などの損傷による出来事記憶の障害に加えて，大脳の後方領域の損傷によりいろいろなことが「できなくなる認知症」である．前頭側頭型認知症は，側頭葉先端部の損傷による意味記憶の障害に加えて，前頭葉の損傷により保たれている大脳後方領域の機能を不適切に行使する「してしまう認知症」である．Lewy小体型認知症では共通の病態によりAlzheimer病と似た症状が出るほか，眼窩前頭皮質，扁桃体，側頭葉下面，脳幹の諸核などの損傷により，独特の妄想，幻視や錯視，夢の中どおりに体が動く，Parkinson症状，症状の著しい変動などが起こる．

　Alzheimer's disease, frontotemporal dementia, and dementia with Lewy bodies are neurodegenerative diseases which are the major causes of dementia. In Alzheimer's disease, the degeneration initially takes place in the hippocampus and the posterior half of the cortex, i.e. the parietal lobe and the posterior temporal lobe. This damage causes disorder of episodic memory and loss of abilities that are associated with the posterior cortex, such as reading, writing, word finding, tool use and dressing. In frontotemporal dementia, the degeneration primarily takes place in the anterior half of the cortex, i.e. the most anterior part of the temporal lobe and the frontal lobe. This damage causes loss of some kinds of semantic memories and disordered control of the patient's behavior. Patients inappropriately use preserved abilities associated with the posterior cortex. Dementia with Lewy bodies shows Alzheimer pathology, which causes symptoms similar to Alzheimer's disease. In addition, the characteristic symptoms of this disease are caused by Lewy body pathology found in the orbitofrontal cortex, the amygdale, inferior temporal lobe, and nuclei in the brain stem such as the substantia nigra and locus coeruleus. Such symptoms include delusional misidentification, visual hallucination, illusions, REM sleep behavior disorder, Parkinsonism, and marked fluctuation of symptoms.