Loss of Smell (Anosmia) or impaired sense of smell could be causes by viral infection. However, viral infection rarely causes permanent loss of smell.
The nose is formed by the two nasal bones that articulate with the nasal process of the maxilla on each side to form the nasal cavity. This nasal cavity is divided by the nasal septum to form the left and right nostrils. The lower end of the nose consists of the lateral cartilages which provide support for the nostrils, especially during inspiration.
The nose is one of the sense organs of the body. The important functions of the nose include respiration, filtration of particles, heating, humidification and smell.
The olfactory nerve is responsible for the sense of smell. The olfactory neuroepithelium of the nose is located in the roof of the nasal cavity. These neurons run through the cribriform plate to the olfactory bulb which lies on the floor of the anterior cranial fossa.
The important symptoms of nasal disease include nasal blockage, nasal discharge (rhinorrhea), nasal bleeding (epistaxis), facial pain, excessive sneezing, excessive nasal itching and loss/impaired sense of smell.
Loss of smell or impaired sense of smell is most often caused by nasal obstruction. This prevents airborne molecules from gaining access to the olfactory cleft. Nasal obstruction can be caused by nasal polyps or allergic rhinitis.
Loss of smell or impaired sense of smell can also be caused by damage to the olfactory nerve fibres that pass through the cribriform plate. This damage to the olfactory nerve fibres could result from any injury that affects the head and face which could be in form of assaults, road traffic accidents or falls.
Viral infections could also result to loss of smell or impaired sense of smell. However, they can rarely cause permanent loss of smell. These viral infections can present from common cold to Covid-19. Loss of smell may be one of the initial symptoms of Covid-19.
Covid-19 is a viral infection that is caused by Coronavirus SARS-Cov-2.This virus has been found to have some neurological effects including loss of smell or impaired sense of smell. As with other viral causes of loss of smell, its effect is not permanent.
Reports have shown that 10-30% of covid-19 patients develop central nervous system/neurologic symptoms and complications.
Reports from Autopsy conducted on Covid-19 patients have demonstrated the presence of SARS-Cov-2 in the brain tissue of patients.
These reports have postulated that the virus invades the brain through the nose. This is as evidenced by MRI reports which
demonstrated lesional changes in the olfactory bulbs and right gyrus rectus.
Other central nervous system/neurological symptoms and complications of Covid-19 include loss of sense of taste ( which may also be the initial presentation of the disease) and intravascular coagulation leading to embolic stroke. More so, some adult Post-Covid patients have deranged higher cognitive functions as a neurological complication.