From the Guidelines

Anosmia is the loss or impairment of the sense of smell.

Anosmia can be classified into different types, including:
- Quantitative disturbances: diminished or enhanced sense of smell, which can be further divided into anosmia (loss of smell), hyposmia (reduced sense of smell), or hyperosmia (increased sense of smell) 1
- Qualitative disturbances: distortions of the sense of smell, also known as dysosmia
- Discrimination disturbances: inability to differentiate among various smells

Anosmia can be caused by various factors, including:
- Conduction loss: sinonasal passage obstruction
- Sensorineural loss: olfactory neuroepithelial damage
- Central nervous system disorders: trauma, aging, upper respiratory infections, inflammatory sinonasal disorders, tumors, and neurodegenerative diseases such as Alzheimer's and Parkinson's 1
Anosmia has also been associated with COVID-19, with some studies suggesting that it may be a presenting symptom or an early symptom of the disease 1

Anosmia can be diagnosed through clinical examination and objective testing, such as the "Sniffin' Sticks" test or the odourized markers screening test 1
The diagnosis of anosmia is important, as it can have significant impacts on an individual's quality of life and ability to detect hazards, such as gas leaks or fires.

From the Research

Anosmia is defined as the inability to smell, while hyposmia is a decreased ability to smell 2.
It is estimated that 3-20% of the population is affected by anosmia or hyposmia 2.
The risk of olfactory dysfunction increases with old age and may also result from chronic sinonasal diseases, severe head trauma, and upper respiratory infections, or neurodegenerative diseases 2.

Anosmia can be caused by various factors, including trauma, chronic sinusitis, neoplasms, and respiratory viral infections such as rhinovirus and SARS-CoV-2 3, 4.
Anosmia can lead to a significant impact on quality of life, including impaired ability to sense warning odors, decreased enjoyment of food, and increased risk of depression 2, 5.
People with anosmia may experience weight loss or malnutrition due to decreased interest in eating, and may also have difficulty smelling pleasurable foods 5.

The diagnosis of anosmia typically involves a thorough history and physical, as well as validated orthonasal smell tests such as the Sniffin' Sticks and the UPSIT 3.
Imaging modalities such as MRI and CT may be used to rule out underlying conditions, but are not typically used to diagnose smell loss 3.
Treatment options for anosmia include olfactory training, intranasal corticosteroids, and platelet-rich plasma (PRP) therapy 5, 4.
PRP therapy has shown promise in improving olfactory function, particularly in patients with persistent loss 5.