Diagnostic utility of abbreviated fluency measures in Alzheimer disease and vascular dementia

S J Duff Canning, L Leach, D Stuss, L Ngo, S E Black
Neurology 2004 February 24, 62 (4): 556-62

BACKGROUND: Several studies indicate semantic fluency more sensitively discriminates patients with Alzheimer disease (AD) from normal elderly persons, with disproportionate impairment of semantic over phonemic fluency.

OBJECTIVE: To determine the ability of abbreviated fluency measures in the clinic setting (1-minute letter F and animal fluency tests) to detect AD, and to assess whether difference scores between these measures discriminate patients with AD and vascular dementia (VaD) from normal elderly persons.

METHODS: The authors studied patients with AD (n = 98) meeting National Institute of Neurological Communicative Disorders and Stroke-Alzheimer's Disease and Related Disorders Association criteria, VaD patients (n = 18) meeting National Institute of Neurological Disorders and Stroke-Association Internationale pour la Recherche et l'Enseignement en Neurosciences criteria, cognitively impaired but not demented patients (CIND; n = 25), vascular CIND patients (VCIND; n = 24), and normal control subjects (NCs; n = 46).

RESULTS: Analysis of covariance controlling for age, education, and overall impairment indicated all groups generated fewer animal names compared with NCs, whereas only VaD patients generated fewer letter F words compared with NCs. On standardized scores, patients with AD and CIND, unlike those with VCIND and VaD, scored significantly worse on the animal fluency test than on the letter F fluency test. The animal fluency test was superior in discriminating all patient groups from NCs. Positive likelihood ratios (PLRs) revealed animal fluency scores <15 were 20 times more likely in a patient with AD than in an NC (sensitivity = 0.88; specificity = 0.96). Letter F scores <4 discriminated VaD from AD patients (PLR = 4.0; sensitivity = 0.44; specificity = 0.90). Difference scores <0 (i.e., fewer animal than letter F words) discriminated patients with VCIND from those with CIND (PLR = 2.5; sensitivity = 0.32; specificity = 1.00).

CONCLUSIONS: A 1-minute semantic fluency test can assist in early detection of dementia in the memory clinic setting.

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