title: Feeling of presence in Parkinson's disease.
abstract: BACKGROUND
  A feeling of presence (FP), that is, the vivid sensation that somebody (distinct from oneself) is present nearby, is commonly reported by patients with Parkinson's disease (PD), but its phenomenology has not been described precisely. The objective of this study was to provide a detailed description of FP in PD and to discuss its possible mechanisms.
  
  
  METHODS
  The authors studied 52 non-demented PD patients reporting FP in the preceding month (38 consecutive outpatients and 14 inpatients). FP characteristics were recorded with a structured questionnaire. The outpatients with FP were compared with 78 consecutive outpatients without FP.
  
  
  RESULTS
  About half the patients said they recognised the 'identity' of the presence. More than 75% of patients said the FP were not distressing, were short-lasting, were felt beside and/or behind the patient, and occurred while indoors; most patients checked for a real presence, but their insight was generally preserved. In 31% of cases, the patients had an unformed visual hallucination simultaneously with the FP. A higher daily levodopa-equivalent dose and the presence of visual illusions or hallucinations were independently associated with FP.
  
  
  CONCLUSIONS
  Although FP is not a sensory perception, projection of the sensation into the extrapersonal space, along with the frequent co-occurrence of elementary visual hallucinations and the strong association with visual hallucinations or illusions, supports its hallucinatory nature. FP may be viewed as a 'social' hallucination, involving an area or network specifically activated when a living being is present, independently of any perceptual clue.
authors.affiliation: 1AP-HP, Groupe HospitalierHenri-Mondor, Service deneurologie, Cre´teil, France. gilles.fenelon@hmn.aphp.fr
authors.forename: Gilles
authors.initials: G
authors.lastname: Fénelon
authors.forename: Thierry
authors.initials: T
authors.lastname: Soulas
authors.forename: Laurent
authors.initials: L
authors.lastname: Cleret de Langavant
authors.forename: Iris
authors.initials: I
authors.lastname: Trinkler
authors.forename: Anne-Catherine
authors.initials: AC
authors.lastname: Bachoud-Lévi
mesh_terms: D000368:Aged; D000369:Aged, 80 and over; D016022:Case-Control Studies; D005260:Female; D006212:Hallucinations / Q000150:complications / Q000503:physiopathology*; D006801:Humans; D007980:Levodopa / Q000627:therapeutic use; D008297:Male; D008875:Middle Aged; D009069:Movement Disorders; D010300:Parkinson Disease / Q000150:complications / Q000503:physiopathology*; D010468:Perceptual Disorders / Q000175:diagnosis; D011618:Psychotic Disorders; D011795:Surveys and Questionnaires
chemical_list: D007980:Levodopa