Neurocognitive disorders are the only psychiatric disorders which underlying pathogeny can potentially be determined. This has important implications, for it makes possible the use of biomarkers in order to gain better diagnosis, and opens a door to more accurate treatments. Nonetheless, as biomarkers are not exclusive of a single disorder, the lengths of its utility are still unknown.

To understand the values and limitations of biomarkers in differential diagnosis of dementias.

We present three cases followed in the Neurology ward of our hospital, in which they were admitted for diagnosis and treatment of a subacute form of dementia. Medical history, core symptoms, screening tests for cognitive impairment, MRI, EEG and biomarkers in cerebrospinal fluid were used for diagnosis.

Two cases had consistent clinical features and complementary explorations, and they were respectively diagnosed as Creutzfeldt-Jakob Disease and Lewy Body Dementia; however, the last case showed contradictory results between clinic and complementary explorations, particularly 14-3-3 protein, which was positive and led to the initial diagnosis as Creutzfeldt-Jakob Disease, which was proven wrong once necropsy was practiced.

Although complementary explorations, and biomarkers in particular, are of invaluable utility in the accurate diagnosis of multiple psychiatric diseases, they must always be considered within a context given by biography and clinical features, because, when failing to do so, they can lead to misdiagnosis and delay of correct treatment.