March 17, 2011

Smell test tells disorders apart

Patients with certain autonomic nervous system disorders have impaired odor identification, which could aid in diagnosis.

(iStock photo)
(iStock photo)

Pure autonomic failure (PAF) and multiple system atrophy (MSA) are rare disorders that affect the autonomic nervous system – the control system for sub-conscious functions including blood pressure, digestion and breathing. MSA is more progressive and rapidly fatal, so a simple test that can distinguish the two disorders would be useful.

Emily Garland of the Vanderbilt Autonomic Dysfunction Center and her colleagues evaluated odor identification in patients with PAF, MSA or another disorder – dopamine beta-hydroxylase deficiency (DBHD), in which patients have intact autonomic neurons but do not produce the neurotransmitter norepinephrine. The researchers assessed olfactory function using UPSIT, the University of Pennsylvania Smell Identification Test, and found that odor identification was significantly impaired in patients with PAF, but not in patients with MSA or DBHD.

The findings, reported in the Feb. 1 issue of Neurology, suggest that UPSIT may be useful in the differential diagnosis between PAF and MSA. They also shed light on olfactory function by showing that certain neuronal pathways are important, but that norepinephrine is not essential.