Anosmia: Causes, Diagnosis, and Management of Smell Loss
Anosmia is the complete loss of the sense of smell. Hyposmia is partial loss. Dysosmia (parosmia, phantosmia) is distorted smell perception. Smell loss significantly impairs flavor perception, safety (gas, smoke, spoiled food), and quality of life.
Etiologic Classification
| Category | Mechanism | Causes |
|---|
| Conductive (Obstructive) | Odorants cannot reach olfactory cleft | Chronic rhinosinusitis (CRS) with/without polyps, allergic rhinitis, septal deviation, turbinate hypertrophy, nasal masses/tumors |
| Sensorineural | Olfactory epithelium or neural pathway damage | Post-viral (URI, COVID-19), head trauma (shear injury at cribriform plate), neurodegenerative (Parkinson's, Alzheimer's, Lewy body), aging (presbyosmia), toxins (solvents, heavy metals), radiation, medications (intranasal zinc, some antihypertensives), congenital (Kallmann syndrome) |
| Central | CNS processing deficits | Stroke, tumor, MS, epilepsy, TBI affecting olfactory bulb/tract/cortex |
Diagnostic Workup
- History: Onset (sudden vs. gradual), associated sinonasal symptoms, head trauma, medications, COVID, neurodegenerative signs.
- Exam: Anterior rhinoscopy, nasal endoscopy (polyps, inflammation, anatomy).
- Olfactory Testing: UPSIT (40-item scratch-and-sniff), Sniffin' Sticks (threshold, discrimination, identification), CCCRC.
- Imaging: MRI brain + olfactory bulbs (neurodegenerative, trauma, tumor); CT sinuses (conductive causes).
- Labs: TSH, B12, Zn, Cu, ANA, HIV, Lyme (if systemic cause suspected).
Management
- Conductive: Treat underlying (intranasal corticosteroids ± oral for polyps, antihistamines, surgery — FESS, septoplasty, polypectomy).
- Post-viral / Post-COVID: Olfactory training (4 odorants: rose, lemon, clove, eucalyptus 2×/day × 12+ weeks), topical corticosteroids, omega-3, vitamin A drops (limited evidence), time (recovery up to 1–2 yrs).
- Neurodegenerative: No disease-modifying Rx; safety counseling (smoke/CO detectors, food labeling).
- Medication-induced: Discontinue offending agent if possible.
Prognosis
- Conductive: Often reversible with treatment.
- Post-viral: 30–60% recover partially/fully over months-years.
- Traumatic: <10% if olfactory nerve severed.
- Neurodegenerative: Progressive; anosmia often precedes motor/cognitive symptoms by years.
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