Current Challenges in the Diagnosis of Progressive Neurocognitive Disorders: A Critical Review of the Literature and Recommendations for Primary and Secondary Care

Abstract

Screening for early symptoms of cognitive impairment enables timely interventions for patients and their families. Despite the advances in dementia diagnosis, the current nosography of neurocognitive disorders (NCDs) seems to overlook some clinical manifestations and predictors that could contribute to understanding the conversion from an asymptomatic stage to a very mild one, eventually leading to obvious disease. The present review examines different diagnostic approaches in view of neurophysiological and neuropsychological evidence of NCD progression, which may be subdivided into: (1) preclinical stage; (2) transitional stage; (3) prodromal or mild stage; (4) major NCD. The absence of univocal criteria and the adoption of ambiguous or narrow labels might complicate the diagnostic process. In particular, it should be noted that: (1) only neuropathological hallmarks characterize preclinical NCD; (2) transitional NCD must be assessed through proactive neuropsychological protocols; (3) prodromal/mild NCDs are based on cognitive functional indicators; (4) major NCD requires well-established tools to evaluate its severity stage; (5) insight should be accounted for by both patient and informants. Therefore, the examination of evolving epidemiological and clinical features occurring at each NCD stage may orient primary and secondary care, allowing for more targeted prevention, diagnosis, and/or treatment of both cognitive and functional impairment.

Keywords: cognitive impairment; diagnostic criteria; neurocognitive disorders; stadial progression.

Figure 1

Graphical representation of four conventional stages of neurocognitive decline and cognitive impairment no dementia (CIND). The diagram shows the possible gradual progression of neurocognitive disorders from the preclinical stage to the onset of dementia. Abbreviations: AD = Alzheimer’s disease; CIND = cognitive impairment no dementia; DSM-5 = Diagnostic and Statistical Manual of Mental Disorders, 5th edition; NCD = neurocognitive disorder.

Figure 2

Graphical representation of the markers or indices covered by assessment procedures over the neurocognitive continuum. The figure summarizes selected measures and information that can be collected to support diagnosis and prognosis according to the most widely adopted classification models. Abbreviations: AD = Alzheimer’s disease; CSF = cerebrospinal fluid; CIND = cognitive impairment no dementia; MRI = Magnetic Resonance Imaging; NCD = neurocognitive disorder; PET = positron emission tomography.