Some Causes of Anosmia

Intranasal obstruction

Allergic rhinitis

History of chronic allergic symptoms (eg, congestion, clear rhinorrhea); no pain

History and physical examination

Allergen skin testing (percutaneous/intradermal)

Allergen blood testing (specific IgE)

Nasal polyps

Polyps usually visible during examination

History and physical examination alone

Sometimes nasal endoscopy (rhinoscopy)

Destruction of olfactory neuroepithelium

Atrophic rhinitis

Chronic rhinitis with atrophic and sclerotic mucous membranes, patency of nasal passages, crust formation, a foul odor

History and physical examination alone

Sometimes biopsy, which shows the normal ciliated columnar epithelium converted to stratified squamous (squamous metaplasia) and the lamina propria reduced in amount and vascularity

Chronic sinusitis

Chronic mucopurulent drainage, documented infections

History and physical examination alone

Sometimes CT

COVID-19*

Onset often precedes other symptoms of infection (eg, fever, cough)

Viral testing when available

Some viral URIs

Onset after clinical infection

History and physical examination alone

Medications and illicit drugs (eg, amphetamines, enalapril, estrogen, naphazoline, phenothiazines, reserpine; prolonged use of decongestants)Medications and illicit drugs (eg, amphetamines, enalapril, estrogen, naphazoline, phenothiazines, reserpine; prolonged use of decongestants)

Usually, an apparent history of use

History and physical examination alone

Toxins (eg, cadmium, manganese)Toxins (eg, cadmium, manganese)

Usually, an apparent history of exposure

History and physical examination alone

Tumors (eg, meningioma, olfactory neuroblastoma)†

Only anosmia or possibly visual difficulty (if the tumor impinges on the optic chiasm or olfactory groove)

CT

MRI

Destruction of central pathways

Alzheimer disease

Progressive confusion and loss of recent memory

MRI

Sequential memory tests

Degenerative neurologic disorders (eg, multiple sclerosis)

Intermittent episodes of other neurologic symptoms (eg, weakness;, numbness; difficulty speaking, seeing, or swallowing

MRI

Sometimes lumbar puncture

Head trauma

Apparent by history

CT or MRI

Intracranial surgery, infection, or tumor

Surgery and CNS infection apparent by history

Tumors with or without other neurologic symptoms

CT or MRI