Depression as a Prodromal Symptom of Neurodegenerative Diseases

Neurodegenerative diseases can manifest as psychiatric symptoms in the prodromal phase, before the onset of core symptoms such as neurological, motor, and cognitive symptoms. Positron emission tomography (PET) has made it possible to detect the pathology of some neurodegenerative diseases in vivo. Many studies have indicated that depression is a preclinical symptom of neurodegenerative diseases. Approximately 10% of non-demented participants with depression developed Alzheimer's disease (AD) during the follow-up period. The prevalence of depression/dysphoria was 42.9% in the preclinical stage of dementia with Lewy bodies. Depression was present in 33.3% of patients with preclinical behavioral-variant frontotemporal lobar degeneration. Approximately 10% of patients had a history of depression at the time of diagnosis with Parkinson's disease. PET studies have revealed the pathology of neurodegenerative diseases in some cases of geriatric depression. Increased brain amyloid-beta deposition in late-onset depression is a possible reflection of prodromal AD. The severity of depression was significantly associated with greater inferior temporal tau and marginally associated with greater entorhinal cortex tau, and depression was associated with significantly greater mean cortical tau deposition. Thus, the presence of depression as a preclinical/prodromal symptom of neurodegenerative diseases has been demonstrated by epidemiological, pathological, and biomarker studies. A growing body of evidence from PET studies indicates that some cases of geriatric depression have pathologies of degenerative neurological disease. In the future, it is expected that PET will be utilized as an imaging biomarker for diagnosis of psychiatric disorders and development of new therapeutic agents.