Traumatic Brain Injury and Olfaction: A Systematic Review

Abstract

Traumatic brain injury (TBI) is a common condition that is often complicated by neuropsychiatric sequelae that can have major impacts on function and quality of life. An alteration in the sense of smell is recognized as a relatively common complication of TBI; however in clinical practice, this complication may not be sought or adequately characterized. We conducted a systematic review of studies concerned with olfactory functioning following TBI. Our predetermined criteria led to the identification of 25 studies published in English, which we examined in detail. We have tabulated the data from these studies in eight separate tables, beginning with Table 1, which highlights each study’s key findings, and we provide a summary/synthesis of the findings in the accompanying results and discussion sections. Despite widely differing methodologies, the studies attest to a high frequency of post-TBI olfactory dysfunction and indicate that its presence can serve as a potential marker of additional structural or functional morbidities.

Impact of BDNF Val66Met polymorphism on olfactory functions of female concussed athletes

“…In a recent systematic review, authors found that hyposmia (reduced olfactory function) was present in 20-40% of mild traumatic brain injury (TBI) patients [42]. From those mild TBI patients who experience hyposmia, $10% recover naturally from post-traumatic olfactory loss [44].…”

“…The olfactory system stands out as a relevant study target to investigate the mediating effects of the BDNF val66met polymorphism on long-term brain sequelae after concussion considering that (1) olfactory dysfunction is highly prevalent after concussive injury and its presence can serve as a potential marker of additional structural or functional morbidities [42]; (2) the olfactory bulb is among a few brain structures that has the ability to regenerate itself through BNDF-dependent brain plasticity and neurogenesis processes [43]; and (3) BDNF plays a central role in olfactory function [43]. In a recent systematic review, authors found that hyposmia (reduced olfactory function) was present in 20-40% of mild traumatic brain injury (TBI) patients [42].…”

Olfaction and traumatic head injury - Is it possible to discriminate between malingering and patients with smell disorders based on nowadays knowledge?

“…Still, other studies reported that frontal lesions were associated with worse performance on olfactory tests 65 .…”

“…Nowadays, it is well known, though even minor THI could determine anosmia 64 . Within the reviewed clinical studies, the reported prevalence of patients with olfactory complaints among cases with "mild" THI was between 20% -44%; among those with "moderate" THI: 37% -68.4%; with "moderate to severe" THI: 49% -56%; and with severe THI: 33% -61% 65 .…”

“…The following are important: traumatic head injury severity -often defined by the Glasgow Coma Score (GCS), the duration of post-traumatic amnesia (PTA), the moment when the loss of smell occurred and the duration of loss of consciousness (LOC) and also other investigations that the clinician can perform immediately following THI. Also, if the patient's health condition permits, following THI, it is recommended to evaluate the functional outcome (neuropsychological test performance, behavioural tests or other functional questionnaires) 65 . Additionally, one must insist on the olfactory status before the THI.…”