Corticobasal syndrome (CBS) is a combination of extrapyramidal disorders (asymmetric parkinsonism, dystonia, myoclonia) and cortical disorders (apraxia, disorders of complex types of sensitivity, the alien limb phenomenon). Most often, CBS is associated with corticobasal degeneration (CBD) or Alzheimer’s disease (AD). In some cases, differential diagnosis between these diseases based only on clinical and neuroimaging data is challenging. Biological markers for AD may prove crucial in establishing an accurate diagnosis. Two cases of patients with CBS and Alzheimer-type memory disorders are presented. Asymmetric cortical atrophy was detected by brain MRI. In the presented cases, patients showed a significant decrease in the Aβ₄₂ levels in the cerebrospinal fluid, which helped to establish the diagnosis of AD. The issues of differential diagnosis of BSC associated with CBS and AD are discussed. The use of biomarkers for atypical clinical manifestations of AD may help to make a diagnosis early. Accurate diagnosis of AD is necessary both for the timely administration of available symptomatic drugs and for determining the indications for pathogenetic anti-amyloid therapy.