1 M. Merello, S.E. Starkstein (eds.), Movement Disorders in Dementias, DOI 10.1007/978-1-4471-6365-7_1, © Springer-Verlag London 2014 Abstract Neurodegenerative diseases encompass several entities characterized by variable clinical features. Clinical presentation, anatomical regions affected, neuro- pathology, or molecular aspects of this group of diseases overlap frequently, render- ing the “perfect” classification an almost impossible mission in many cases despite presence of the hallmark molecular findings. In this chapter, we will review the different classifications of neurodegenerative disorders as well as the artificial boundaries between movement disorders and dementias. Keywords Dementia • Parkinsonism • Amyloidopathies • Tauopathies • Synucleinopathies • FUSpathies • Filament inclusion disorders Introduction Neurodegenerative diseases are characterized by death and progressive loss of neu- rons in distinct areas of the central nervous system. Classification is based on clini- cal presentation, anatomical regions affected, inclusion bearing cell type, and conformational protein altered. Clinical features resulting from these mechanisms reflect which anatomical regions or functional systems are affected by neuronal damage and include cognitive decline, dementia, alteration in high-order brain func- tions, movement disorders, or, in the majority of cases, a combination of all of these. Chapter 1 Neurodegenerative Disorders: Dementia and Parkinsonism, Lumping Together or Splitting Apart? Marcelo Merello and Malco Rossi M. Merello, MD, PhD (*) Neuroscience Department, Raul Carrea Institute for Neurological Research (FLENI), Universidad Catolica Argentina, Buenos Aires, Argentina e-mail: mmerello@fleni.org.ar M. Rossi, MD Movement Disorders Section, Neuroscience Department, Raul Carrea Institute for Neurological Research (FLENI), Buenos Aires, Argentina