A history of head injuries could impact your sense of smell
A history of head injuries could make you more likely to experience a loss of your sense of smell, according to a team of international researchers.
The study, published in the journal JAMA Otolaryngology-Head & Neck Surgery, found that out of 5,961 participants - including 1,666 people who had a history of head injuries - those who had suffered from at least two head injuries or had more severe injuries were more likely to report a loss of smell.
If you’ve ever had a nose full of snot during a severe cold or sinus infection, you’ve likely experienced a temoorary bout of anosmia - a full or partial loss of your sense of smell - but it can also be permanent.
The team reported that 24 percent of those with a history of head injuries self-reported a loss of smell, in comparison to 20 percent of those with no head injuries, with 15 percent having objective anosmia versus 13 percent in the cohort with no injuries.
For those with traumatic brain injuries (TBI), previous studies have found that 14 to 20 percent suffer from a loss of smell, with this most-recent study finding that the likelihood of suffering from smell loss relied on both the number of head injuries and their severity.
The researchers found that both self-reporting a loss of smell and being objectively assessed to have anosmia were associated with a person having a history of at least two head injuries which were moderate, severe or penetrating.
As for how TBIs cause a loss of smell, the authors suggest that it could include the shearing of the olfactory nerve fibres anchored to the cribriform plate, a part of the ethmoid bone that is anchored in the nasal cavity that is covered in holes to allow for nerves to convey smells to the brain.
They also suggest that injuries to the sinonasal tract, olfactory bulbs, and olfactory-eloquent cortical brain regions could be behind smell loss, but note that other factors such as severe depression, posttraumatic epilepsy, and medications prescribed to manage TBIs could be responsible.
Surprisingly, the team reported that a high proportion of participants were unaware of the extent of their loss of smell, echoing findings from previous studies.
They found that those with a history of head injuries were more likely to under-report or over-report the extent of their smell loss - which was also measured using objective olfactory testing - in comparison to those who hadn’t suffered a head injury.
Given that a loss of smell is often inaccurately reported by those with head injuries and that it is associated with negative effects on mental and physical health, the team argue that their study has important considerations for health practitioners working with patients with a history of head injuries.
“Findings also suggest important clinical considerations for the diagnosis and treatment of posttraumatic olfactory loss; that individuals with remote prior head injury are at risk for posttraumatic olfactory dysfunction but are unlikely to be aware of their deficits; and conversely, that individuals with prior head injury may be more likely to overreport subjective olfactory deficits, which may not be confirmed by objective testing,” they write.
“Taken together, there should be consideration of objective psychophysical olfactory assessment in patients with head injury.”
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