About the disease
Anosmia
(loss of smell)
The loss of smell is one of the most common symptoms seen in COVID positive patients, now affecting millons of people. In many people, anosmia is an early sign and will eventually resolve on its own. In others, however, the loss of smell can persist for long periods of time and can even become permanent. When managing anosmia, we first need to categorize it as conductive or neural.
Conductive anosmia occurs when there is either too much swelling in the nose or something is physically blocking the odors from reaching the smell (olfactory) nerve fibers. This type of anosmia is usually more straightforward to treat, since once the nasal obstruction is managed the sense of smell will spontaneously return to normal.
Neural anosmia occurs in two ways: 1) the receptors of the olfactory nerve in the nose are injured and therefore unable to transmit the sensation of odor to the brain or 2) the parts of the brain responsible for processing the smell signal become damaged.
Unfortunately, the exact cause of COVID-19 related anosmia is still controversial. Studies examining COVID patients with MRI scans suggest that it may be neural, as direct disruption of the olfactory nerve fibers cause this area to light up on brain scans. Other reports suggest the anosmia may be conductive from disruption or damage to the tissues that surround the nerves, thereby blocking odors from reaching the nerve endings. Because of these conflicting theories, the exact pathogenesis of injury is still widely unknown.