Some Causes and Features of Anosmia

Cause

Common Features*

Diagnostic Approach

Blockage within the nose

Nasal allergies

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

Nasal polyps

Polyps that are usually seen during the examination

A doctor's examination alone

Destruction of smell receptors‡

Atrophic rhinitis

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

Chronic sinusitis

A thick, foul-smelling nasal discharge most or all of the time

Previous sinus infections

Sometimes a doctor's examination alone

Usually CT

COVID-19

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

Alzheimer disease

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

Head injuries

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.

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