title: Subjective cognitive impairment: Towards early identification of Alzheimer disease.
abstract: BACKGROUND
  Neurodegeneration in Alzheimer disease (AD) begins decades before dementia and patients with mild cognitive impairment (MCI) already demonstrate significant lesion loads. Lack of information about the early pathophysiology in AD complicates the search for therapeutic strategies.Subjective cognitive impairment is the description given to subjects who have memory-related complaints without pathological results on neuropsychological tests. There is no consensus regarding this heterogeneous syndrome, but at least some of these patients may represent the earliest stage in AD.
  
  
  METHODS
  We reviewed available literature in order to summarise current knowledge on subjective cognitive impairment.
  
  
  RESULTS
  Although they may not present detectable signs of disease, SCI patients as a group score lower on neuropsychological tests than the general population does, and they also have a higher incidence of future cognitive decline. Depression and psychiatric co-morbidity play a role but cannot account for all cognitive complaints. Magnetic resonance imaging studies in these patients reveal a pattern of hippocampal atrophy similar to that of amnestic mild cognitive impairment and functional MRI shows increased activation during cognitive tasks which might indicate compensation for loss of function. Prevalence of an AD-like pattern of beta-amyloid (Aβ42) and tau proteins in cerebrospinal fluid is higher in SCI patients than in the general population.
  
  
  CONCLUSIONS
  Memory complaints are relevant symptoms and may predict AD. Interpatient variability and methodological differences between clinical studies make it difficult to assign a definition to this syndrome. In the future, having a standard definition and longitudinal studies with sufficient follow-up times and an emphasis on quantifiable variables may clarify aspects of early AD.
authors.affiliation: Servicio de Neurología, Hospital Clínico San Carlos, Madrid, España; Department of Neurobiology, Care Sciences and Society, Karolinska Institutet, Estocolmo, Suecia. Electronic address: saragptacek@gmail.com.
authors.forename: S
authors.initials: S
authors.lastname: Garcia-Ptacek
authors.affiliation: Department of Neurobiology, Care Sciences and Society, Karolinska Institutet, Estocolmo, Suecia; Department of Geriatric Medicine, Karolinska University Hospital, Karolinska Institutet/Stockholm University, Estocolomo, Suecia.
authors.forename: M
authors.initials: M
authors.lastname: Eriksdotter
authors.affiliation: Department of Neurobiology, Care Sciences and Society, Karolinska Institutet, Estocolmo, Suecia; Department of Geriatric Medicine, Karolinska University Hospital, Karolinska Institutet/Stockholm University, Estocolomo, Suecia.
authors.forename: V
authors.initials: V
authors.lastname: Jelic
authors.affiliation: Servicio de Neurología, Hospital Clínico San Carlos, Madrid, España.
authors.forename: J
authors.initials: J
authors.lastname: Porta-Etessam
authors.affiliation: Aging Research Center, Karolinska Institutet and Stockholm University, Estocolmo, Suecia; Institute of Gerontology, School of Health Sciences, Jönköping University, Jönköping, Suecia.
authors.forename: I
authors.initials: I
authors.lastname: Kåreholt
authors.affiliation: Servicio de Neurología, Hospital Infanta Cristina, Parla, Madrid, España.
authors.forename: S
authors.initials: S
authors.lastname: Manzano Palomo
mesh_terms: D000544:Alzheimer Disease / Q000175:diagnosis* / Q000523:psychology; D003072:Cognition Disorders / Q000175:diagnosis* / Q000523:psychology; D060825:Cognitive Dysfunction / Q000175:diagnosis* / Q000523:psychology; D042241:Early Diagnosis; D006801:Humans
keywords: Alzheimer disease; Amiloide; Amyloid; Biomarcadores; Biomarkers; Deterioro cognitivo subjetivo; Enfermedad de Alzheimer; Estadio preclínico de enfermedad de Alzheimer; Preclinical stage of Alzheimer disease; Quejas cognitivas subjetivas; Subjective cognitive complaints; Subjective cognitive impairment