Objective: Olfactory dysfunction due to SARS-CoV-2 infection as a prodromal stage of PD.

Background: Olfactory dysfunction due to SARS-CoV-2 disease can depend on the neuroinvasive properties of the virus, which could reach the olfactory bulb (OB) through the olfactory mucosa and neurons. The presence of OD, common in early parkinsonism, added to the evidence of cases of parkinsonism after COVID, highlight the link between SARS-CoV-2 infection and parkinsonism.

Method: Individuals healed from a previous SARS-CoV-2 infection were recruited by the SARS-CoV-2 Unit of the SS Annunziata Hospital, Chieti, Italy. Participants were examined by movement disorder specialists, tested with olfactory smart threshold test (OST) and with olfactory event-related potentials (OERPs) and underwent 123I-FP-CIT SPECT imaging.

Clinical evaluations included a neurological examination with Unified Parkinson’s Disease Rating Scale (UPDRS)(12). All clinical assessments were conducted by investigators blinded to imaging data and vice versa. 

Results: Patient 1 is a 49 y.o. woman, with no medical or pharmacological history. She was infected with SARS CoV2 during the first pandemic wave, in April 2020, without relevant respiratory symptoms; she reported early anosmia e ageusia. Her neurological examination was normal; her UPDRS part III was = 0. A DAT SPECT showed “minimal reduction in tracer concentration in the posterior portion of the putamen bilaterally”.

Patient 2 is 75 y.o. woman, with hypertension. No history of neurological disorders. She had Covid19 in May 2021 and was treated at home, and she reported severe hyposmia. She had mild extrapyramidal signs (mild rigidity of the upper arms, and mild disturbances during the foot tapping test, the left side more than the right side). Her UPDRS part III was =6, Hoen-Yahr scale=1.

She underwent DAT SPECT which showed “minimal reduction in tracer concentration in the posterior portion of the putamen bilaterally”.

Conclusion: 123I-FP-CIT SPECT will show the damage of basal ganglia in patients with persistent OD after SARS-Cov2 infection, highlighting the presence of an olfactory-nigral dysfunction and pre-clinical signatures of PD. Once in the OB, the virus travelling along dopaminergic pathway/olfactory neurons could retrogradely attack other dopaminergic cells in the mesencephalic nuclei, e.g. the substantia nigra, with consequent effect on striatal neurons.

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