Combining olfactory test and motion analysis sensors in Parkinson's disease preclinical diagnosis: a pilot study

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It is widely accepted that the neuropathological process of Parkinson's disease (PD) begins years before the appearance of motor signs. The preclinical phase of PD is believed to last 5‐8 years during which the neuropathological process has begun, but there is no clinical evidence of motor disturbances (tremor, bradykinesia, rigidity). Therefore, preclinical diagnosis of PD could be very important to test agents that could be truly neuroprotective and to better understand pathological history of PD.1
Definite criteria for preclinical diagnosis of PD are still lacking, so this is a topic of great interest and in constant evolution.3
The diagnosis of PD rests mainly on clinical criteria, although sometimes functional imaging of the nigrostriatal dopaminergic system could be useful (ie single‐photon emission computed tomography—SPECT using [123I]‐FP/CIT, a ligand of presynaptic dopamine transporter—DAT). Nevertheless, to achieve preclinical diagnosis, the use of such techniques seems to be mandatory, to confirm a subclinical dysfunction of the nigrostriatal pathway.2
Hyposmia is one of the symptoms that very often precede the appearance of cardinal motor symptoms of PD. Despite its high sensitivity, the specificity of hyposmia in predicting PD is quite low.5 For this reason, hypothesizing a mass screening to achieve preclinical diagnosis, combining detection of olfaction with [123I]‐FP/CIT SPECT seems impractical, considering the cost and the invasiveness of the latter.5 For this reason, there is an unmet need to find low‐cost non‐invasive screening techniques that could discriminate, among subjects with idiopathic hyposmia, those with a probable underlying initial neurodegenerative process, who could possibly undergo [123I]‐FP/CIT SPECT brain imaging.5
In preclinical PD, there could be a progressive or step‐like reduction in motor performances until the disease becomes clinically evident. This subclinical reduction in motor abilities might not be perceived by the patient nor by the clinician.
Wearable devices for motion analysis 6 could be useful in detecting a subclinical reduction in motor skills.
We presume that by studying a population of idiopathic hyposmia with this type of sensors,6 we could find a subgroup of individuals that worsen in motor performances in time. In this subgroup of hyposmic individuals, we also could expect a response to dopaminergic drug challenge using our wearable devices to monitor the changes in motion parameters. We also think that many individuals in this subgroup should have positive results in [123I]‐FP/CIT SPECT brain imaging.
Given these hypotheses, we did a pilot study and here we show the results.
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