Encephalopathies are a group of central nervous system (CNS) affection with heterogeneous etiology. Several causes have been recognized including neurodegenerative, vascular, infectious, autoimmune, toxic or allergic affections or secondary to systemic disorders. While 30-50% of acute encephalitis remains without etiological definition, definitive criteria for neurodegenerative diseases are usually unavailable in vivo and possible or probable definitions are used. The Olfactory mucosa (OM) is the part of the nasal mucosa that carries the specialized sensory organ for the modality of smell; the olfactory epithelium is composed of five principal cell types including olfactory receptor neurons. A sample of OM may be collected through a rhinoscopy-guided brushing: it is well-accepted by patients, not-contraindicated in patients with raised intracranial pressure and associated with almost no side-effects. Nasal brushing has recently been proposed for the in vivo diagnosis of Creutzfeldt-Jakob disease (CJD).