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12-03-2013 | Physiology | Article

Autonomic function aids dementia diagnosis

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medwireNews: Sympathetic skin response (SSR) and heart rate variability (HRV) can help to distinguish patients with dementia with Lewy bodies (DLB) from those with Alzheimer's disease (AD), study findings suggest.

Study co-author Hiroaki Yoshikawa (Kanazawa University, Ishikawa, Japan) and colleagues believe that these measurements could substitute for a 123I-metaiodobenzylguanidine (MIBG) scan. Although useful for distinguishing DLB from AD, "the utilisation of a radioisotope, high running costs and long testing time prevent the MIBG scan from becoming a routine clinical examination," they write in the BMJ Open.

The study included 20 patients with probable AD, based on clinical criteria, and 20 with probable DLB.

On SSR testing, most DLB patients had little or no reaction to nerve electrical stimulation, whereas most AD patients had a marked response. This clear difference was observed despite SSR being difficult to reproduce, notes the team. Likewise, HRV, measured as the ratio of low- to high-frequency power, was significantly reduced in patients with DLB relative to those with AD.

The patients then underwent a MIBG scan as a more direct assessment of sympathetic activity. Relative to the MIBG findings, SSR at a cutoff of 0.90 mV and HRV at a cutoff of 0.933 were 85% and 90% sensitive, respectively, and were each 85% specific, for distinguishing DLB from AD.

In total, 15 of the DLB patients, but just one of the AD patients had abnormal findings for both SSR and HRV. All DLB patients had abnormal measurements for either SSR or HRV, compared with just seven of those with AD.

Besides the one patient who had abnormal SSR and HRV but was classified as having AD, there were three with isolated abnormal SSR and three with isolated abnormal HRV who also had normal MIBG scans.

"We should follow these patients for their clinical manifestations," say Yoshikawa et al.

By Eleanor McDermid, Senior medwireNews Reporter

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