Neurocognitive disorders (TNC) are of a public health concern. An early and accurate diagnosis is important to tailor a personalised care. We illustrate the importance of a graduated etiological diagnostic approach centered on the clinical presentation employing the case of a patient with a progressive neurovisual disorder suggestive of a common form of Alzheimer's disease. The results of the CSF biomarkers analysis argue against this diagnosis and justifies seeking a Lewy body disease as a differential diagnosis even if all the clinical criteria are initially incomplete. In this article, we illustrate the progressive and graduated approach in the use of complementary medical tests available for reliable and early diagnosis in order to optimise the care plan and predict clinical progress and needs.