The pandemic produced a tsunami of clinical papers on COVID-related smell loss. Investigations of possible treatments, however, are in short supply.
A new paper finds that electrical brain stimulation (anodal transcranial direct current stimulation, or A-tDCS), combined with olfactory training, significantly improved odor perception in a small group of COVID smell loss patients.
The research team, based in Genoa, Italy, studied seven patients. The patients were given olfactory training which consisted of sniffing ten odors (rose, eucalyptus, lemon, etc.) in daily sessions for two weeks. Their sense of smell was objectively evaluated using the Sniffin’ Sticks odor identification test. They also provided self-ratings of their smell ability.
During the olfactory training the patients wore a TDCS stimulator with the anode placed over the left prefrontal cortex and the cathode on the contralateral shoulder. For the first two weeks the device was not activated during training; this was a “sham” control period. For the next two weeks, the TDCS stimulator was active during training. Neither the test administrator or the patient was aware of the TDCS status, thus making the study “double-blind.”
The results were striking and statistically significant. At the end of the first two weeks (the sham period) there was no change from baseline in objective or subjective rating of smell performance. At the end of the next two weeks there was significant improvement in Sniffin’ Stick scores as well as self-ratings. This level of improved performance was maintained at a 3-month followup.
TDCS is a simple and fairly benign intervention: the battery operated unit delivers only 1.5 mA at the scalp. This is quite a distance from the orbitofrontal cortex, the olfactory processing area where the beneficial effect is presumed to happen, leaving plenty of room for skepticism. Still, these are interesting results that merit a larger, fully counterbalanced study.
Lucilla Vestito, Laura Mori, Carlo Trompetto, Diego Bagnasco, Rikki F Canevari, Marta Ponzano, Davide Subbrero, Ester Cecchella, Cristina Barbara, Piero Clavario and Fabio Bandini. (2023). Impact of tDCS on persistent COVID-19 olfactory dysfunction: a double-blind sham-controlled study. Journal of Neurology, Neurosurgery & Psychiatry 94:87.