Merck Manual

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Some Causes and Features of Anosmia

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

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

Previous sinus infections

Sometimes a doctor's examination alone

Usually computed tomography (CT)

Loss of smell is often followed by other symptoms of infection (for example, fever or cough)

Viral testing when available

Drugs (such as amphetamines, enalapril, estrogen, naphazoline, phenothiazines, and reserpine or use of decongestants for a long time)

Usually in people who report taking such drugs

A doctor's examination alone

Loss of smell that occurs after an infection

A doctor's examination alone

Toxins (such as cadmium and manganese)

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

Magnetic resonance imaging (MRI) or CT

Destruction of olfactory pathways in the brain

Progressive confusion and loss of recent memory

MRI

Neuropsychologic (for example. memory) tests

In people who have had brain surgery or a brain infection

CT or MRI

Sometimes headache and/or symptoms of nervous system dysfunction

CT or MRI

Intermittent episodes of other 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.

‡ Destruction of smell receptors has not yet been confirmed as the mechanism for anosmia.