Objective The purpose of this study is to investigate the usefulness of sympathetic skin response (SSR) and heart rate variability (HRV) for the differential diagnosis of patients with dementia with Lewy bodies (DLB).

Design A diagnostic test study.

Setting Single centre in Japan.

Participants We examined 20 patients with probable Alzheimer's disease (AD) diagnosed with NINCDS-ADRDA criteria and 20 with probable DLB diagnosed with the criteria of the third international DLB workshop.

Methods For the SSR measurement, surface electrodes were used: the active recording electrode was placed on the palm of the hand and the reference electrode was placed on the dorsum of the same hand. SSR was induced by a median nerve electrical stimulation at an amplitude of 20 mA. For the HRV measurement, the A–A intervals were measured twice for 2 min with an interval of 5 min in a sitting position after a rest of 5 min. From the low-frequency power (LF; 0.02–0.15 Hz) and high-frequency power (HF; 0.15–0.50 Hz), the ratio of LF to HF power (LF/HF) was calculated using the maximal entropy method.

Results SSR and HRV could detect the abnormality of autonomic function in patients with DLB at sensitivities of 85% and 90%, respectively. On the other hand, SSR and HRV detected an abnormality of autonomic function in patients with AD at sensitivities of 15% and 25% (p<0.05). The combination of the SSR and the HRV (double-positive) indicated abnormal autonomic function was recorded in only 1 of 20 patients (5%) with AD. In contrast, this combination indicated autonomic abnormality in 15 of 20 patients with DLB by our criteria (75%).

Conclusions SSR and HRV can be applied to differentiate DLB from AD.