Some Causes and Features of Anosmia
Cause | Common Features* | Diagnostic Approach |
|---|---|---|
Blockage within the nose | ||
In people who have chronic allergy symptoms (such as nasal congestion and a clear discharge) No pain Symptoms that often occur during certain seasons or after exposure to specific substances | A doctor's examination alone | |
Polyps that are usually seen during the examination | A doctor's examination alone | |
Destruction of smell receptors‡ | ||
Thin, hard, dry mucous membranes Widened nasal passages Crusting inside the nose A foul-smelling odor in the nose | Sometimes a doctor's examination alone Sometimes a biopsy | |
A thick, foul-smelling nasal discharge most or all of the time Previous sinus infections | Sometimes a doctor's examination alone Usually CT | |
Loss of smell and often symptoms of infection (for example, fever or cough) | Viral testing when available | |
Usually in people who report taking such drugs | A doctor's examination alone | |
Some viral upper respiratory infections (such as influenza) | Loss of smell that occurs after an infection | A doctor's examination alone |
Usually in people who report exposure to such toxins | A doctor's examination alone | |
Tumors (a rare cause) | Possibly vision problems or only loss of smell | MRI or CT |
Destruction of olfactory pathways in the brain | ||
Progressive confusion and loss of recent memory | MRI Neuropsychologic tests§ | |
Brain surgery or a brain infection | In people who have had brain surgery or a brain infection | CT or MRI |
Brain tumors (a rare cause of loss of smell) | Sometimes headache and/or other symptoms of nervous system dysfunction, such as weakness, numbness, or difficulty speaking, seeing, or swallowing | CT or MRI |
Degenerative neurologic disorders (such as multiple sclerosis) | Intermittent episodes of symptoms of nervous system dysfunction, such as weakness, numbness, or difficulty speaking, seeing, or swallowing | MRI Sometimes a spinal tap |
In people who have had a head injury | CT or MRI | |
* Features include symptoms and results of the doctor's examination. Features mentioned are typical but not always present. | ||
† Although a doctor's examination is always done, it is mentioned in this column only if the diagnosis can sometimes be made by the doctor's examination alone, without any testing. | ||
‡ Neuropsychologic testing is detailed testing that covers the main areas of mental function, including memory and mood. | ||
§ Destruction of smell receptors has not yet been confirmed as the mechanism for anosmia. | ||
CT = computed tomography; COVID-19 = coronavirus disease 2019; MRI = magnetic resonance imaging. | ||