What gray matter (GM) structural changes occur within olfactory-related regions of the brain in patients with smell loss due to upper respiratory tract infection (URTI) before and after olfactory rehabilitation?
Olfactory training (OT) was associated with an increase in GM volume of the hippocampus and the thalamus, which may suggest a strategy for more effective exploitation of olfactory signals based on odors and association of memories with olfactory input.
Explore this issue:July 2018
Background: URTIs are a major cause of olfactory disorders. There is a correlation between olfactory bulb (OB) volume and odor identification. Although studies have shown a correlation between hyposmia and decreased olfactory-related brain region volume, less is known about higher cerebral structural changes that would accompany olfactory recovery.
Study design: Prospective intervention case-control study involving 30 patients with smell loss due to URTI, and 31 controls.
Setting: Technical University of Dresden, Germany.
Synopsis: Patients underwent OT for 12 weeks twice a day. After OT, patients reached significantly higher scores for threshold, discrimination, identification, and combined TDI score. Sixteen patients improved 5.5 or better in TDI, indicating a clinically significant improvement. Significantly reduced GM volume was observed in patients in two clusters, mainly in the hippocampus. No significant cluster in primary olfactory regions could be found comparing controls with patients. There was no GM volume difference in olfactory-related areas between patients with long-term olfactory loss and controls with superior olfactory function. Following OT, patients exhibited a GM volume increase in the hippocampus, thalamus, and cerebellum. Patients with a longer duration of smell disability showed no additional results. There were no significant results for subgroups of pre- and post-OT patients for the correlation between changes in total intracranial volume (TIV), OB volume, and olfactory function. Limitations included a lack of knowledge about compliance, the possibility of some effects being due to spontaneous improvement, and mismatched ages between patient and control groups that could affect TDI and GM volume results.
Citation: Gellrich J, Han P, Manesse C, et al. Brain volume changes in hyposmic patients before and after olfactory training. Laryngoscope. December 14, 2017. doi: 10.1002/lary.27045