A short and simple bedside test to detect cognitive fluctuations in patients with dementia with Lewy bodies.

Background And Purpose: The establishment of cognitive fluctuations is important when dementia with Lewy bodies (DLB) is suspected but can be especially difficult in the absence of a caregiver who lives with the patient. We examined the possibility of using fluctuating scores on a forward (FDS) and a backward digit span (BDS) test as a marker for cognitive fluctuation.

Methods: Patients with DLB (21), other forms of dementia (14 with Alzheimer's disease, 8 with vascular dementia) and 20 controls were asked to perform an FDS and BDS twice, with an interval of 20 min.

Results: Seventy percent of patients with DLB showed evidence of cognitive fluctuations for at least one test, while less than 10% of controls and patients with other dementias did. Evidence of cognitive fluctuations on at least one of both tests classified 83% of patients correctly (i.e. DLB or not), with a sensitivity of 70% and a specificity of 90%.

Conclusions: Repeated forward and backward digit span tests seem a valid, short, easy and inexpensive bedside tool to detect cognitive fluctuations in the diagnostic work-up of DLB, even in the absence of a caregiver, which limits the use of questionnaires.