Anosmia is very common in the Lewy body variant of Alzheimer's disease

J Neurol Neurosurg Psychiatry. 2005 Oct;76(10):1342-7. doi: 10.1136/jnnp.2003.032003.

Abstract

Background: Olfactory abnormalities are reported in Alzheimer's disease and Parkinson's disease. Anosmia appears to be common in dementia with Lewy bodies but not in pure Alzheimer's disease.

Objective: To determine whether anosmia improves discrimination between the Lewy body variant (LBV) of Alzheimer's disease and "pure" Alzheimer's disease.

Methods: 106 cases of necropsy confirmed pure Alzheimer's disease (n = 89) or LBV (n = 17) were reviewed. All had received butanol odour threshold testing. Anosmia was defined as a score < or = 1.0 on a 0-9 point scale. Logistic regression analysis was used to model potential predictors (for example, parkinsonism, smoking, hallucinations) of neuropathological diagnosis and anosmia.

Results: LBV cases had an increased prevalence of anosmia (65%) compared with Alzheimer's disease (23%; odds ratio (OR) = 6.3, p = 0.00045), or normal elderly people (6.7%). Within the dementia cases, the negative predictive value (92%) and specificity (78%) of anosmia were both good; sensitivity for detecting LBV was 65%, but the positive predictive value (PPV) was only 35%. Logistic regression models showed anosmia (OR = 5.4, p = 0.005) and visual hallucinations (OR = 7.3, p = 0.007) were strong independent predictors of Lewy body pathology. When anosmia was added as a core feature to consensus diagnostic criteria for probable Lewy body dementia, five additional cases of LBV were detected (29% increased sensitivity), but with four additional false positives (1% increased discrimination, 4% decreased specificity, 33% decreased PPV).

Conclusions: Anosmia is very common in LBV. Adding anosmia as a core feature improved sensitivity for detecting LBV, but did not improve discrimination between Alzheimer's disease and LBV owing to a concomitant increase in false positives.

Publication types

  • Research Support, N.I.H., Extramural
  • Research Support, Non-U.S. Gov't
  • Research Support, U.S. Gov't, P.H.S.

MeSH terms

  • 1-Butanol
  • Aged
  • Alzheimer Disease / complications*
  • Alzheimer Disease / diagnosis
  • Alzheimer Disease / pathology*
  • Cognition Disorders / diagnosis
  • Cognition Disorders / etiology
  • Female
  • Hallucinations / etiology
  • Humans
  • Lewy Bodies / pathology*
  • Male
  • Neuropsychological Tests
  • Olfaction Disorders / diagnosis
  • Olfaction Disorders / etiology*
  • Olfactory Bulb / pathology
  • Sensitivity and Specificity
  • Severity of Illness Index

Substances

  • 1-Butanol