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Saturday, August 23, 2025

Anosmia


Introduction

Anosmia is defined as the inability to perceive odors.

  • Temporary anosmia is common, usually due to upper respiratory tract infections or allergic rhinitis.

  • Persistent anosmia may indicate chronic sinus disease, nasal polyps, head trauma, or neurological disorders.

  • It has major consequences on quality of life, safety (failure to detect smoke, spoiled food), and emotional wellbeing.

Types of Olfactory Dysfunction

  • Hyposmia – partial loss of smell.

  • Anosmia – complete loss of smell.

  • Parosmia – distorted sense of smell.

  • Phantosmia – smelling odors that are not present.

Causes of Anosmia

1. Nasal / Sinus Causes (most common, conductive anosmia)

  • Viral upper respiratory infections (common cold, influenza, COVID-19).

  • Allergic rhinitis.

  • Chronic sinusitis.

  • Nasal polyps.

  • Deviated nasal septum.

  • Tumors (rare) blocking nasal passages.

2. Neurological Causes (sensorineural anosmia)

  • Head trauma: shearing of olfactory nerve fibers.

  • Neurodegenerative diseases:

    • Parkinson’s disease.

    • Alzheimer’s disease.

  • Brain tumors: olfactory groove meningioma, frontal lobe tumors.

  • Multiple sclerosis.

3. Infectious / Inflammatory

  • Post-viral olfactory loss (including after COVID-19 infection).

  • Chronic infections (fungal sinusitis).

4. Systemic / Metabolic Causes

  • Hypothyroidism.

  • Diabetes mellitus.

  • Vitamin B12 and zinc deficiency.

  • Chronic kidney or liver disease.

5. Drug-Induced

  • Intranasal zinc sprays.

  • Chemotherapy agents.

  • Certain antibiotics (streptomycin, aminoglycosides).

  • Antihypertensives (enalapril, amlodipine in rare cases).

6. Congenital

  • Kallmann syndrome (anosmia + hypogonadism).

  • Congenital absence of olfactory bulbs.

Clinical Features

  • Inability to detect odors.

  • Reduced ability to taste flavors (since smell contributes to taste).

  • Appetite loss, weight changes.

  • Safety risks (cannot detect gas leaks, smoke, spoiled food).

  • Emotional consequences: depression, social withdrawal.

Associated symptoms depend on cause:

  • Blocked nose, rhinorrhea → rhinitis, sinusitis.

  • Headache, facial pain → sinusitis, tumors.

  • Memory loss, tremor → Alzheimer’s, Parkinson’s.

  • Post-viral onset → often sudden, especially in COVID-19.

Diagnostic Approach

1. History

  • Onset: sudden vs gradual.

  • Relation to infections, trauma, surgery.

  • Associated nasal or neurological symptoms.

  • Medication history.

  • Family history of neurodegenerative disease.

2. Examination

  • Nasal exam (polyps, congestion, deviated septum).

  • Neurological exam (cranial nerves, cognition, movement disorders).

3. Investigations

  • Olfactory function tests: smell identification tests (UPSIT, Sniffin’ Sticks).

  • Nasal endoscopy: visualize nasal cavity and sinuses.

  • CT sinuses: chronic sinusitis, polyps.

  • MRI brain: tumors, neurodegenerative disease, post-trauma changes.

  • Blood tests: thyroid function, vitamin B12, zinc levels.

  • COVID-19 testing if recent acute anosmia.

Management and Treatment

Treatment depends on the underlying cause.

A. General Measures

  • Treat underlying nasal congestion.

  • Good nasal hygiene (saline irrigations).

  • Safety counseling (smoke detectors, careful food storage).

B. Pharmacological Treatment

  1. Nasal / Sinus Disease

  • Allergic rhinitis:

    • Fluticasone nasal spray 50 mcg in each nostril once daily.

    • Cetirizine 10 mg orally once daily.

  • Chronic sinusitis / nasal polyps:

    • Mometasone nasal spray 50 mcg per nostril twice daily.

    • Short course of Prednisone 30 mg orally daily for 5–7 days (severe polyps).

  • Infection:

    • Amoxicillin-clavulanate 875/125 mg orally twice daily × 7–10 days (for bacterial sinusitis).

  1. Post-Viral Anosmia (including COVID-19)

  • Olfactory training therapy: repeated daily exposure to familiar scents (lemon, rose, clove, eucalyptus) for months.

  • Limited evidence for corticosteroids (short course if associated with nasal inflammation).

  1. Neurological / Systemic Causes

  • Treat underlying disorder:

    • Parkinson’s disease: Levodopa-carbidopa.

    • Hypothyroidism: Levothyroxine 50–100 mcg daily, titrated.

    • Vitamin B12 deficiency: Hydroxocobalamin 1 mg IM every 2–3 months.

    • Zinc deficiency: Zinc sulfate 220 mg orally once daily.

C. Surgical Treatment

  • Septoplasty for deviated septum.

  • Endoscopic sinus surgery for chronic sinusitis, polyps.

  • Tumor removal if present.

Complications

  • Reduced taste and appetite → weight loss, malnutrition.

  • Depression, social withdrawal.

  • Increased risk of injury (failure to detect fire, gas leaks, spoiled food).

  • Missed diagnosis of underlying cancer or neurodegenerative disease.

Prognosis

  • Temporary causes (rhinitis, sinusitis, viral infections): good recovery with treatment.

  • Post-viral anosmia (e.g., COVID-19): recovery in 60–80% within 6 months; some remain chronic.

  • Structural causes (polyps, septum deviation): improve with surgery.

  • Neurodegenerative disease: progressive, anosmia often permanent.

  • Congenital anosmia: usually permanent.

Patient Education

  • Anosmia is common and often temporary.

  • Maintain good nasal health (saline rinses, treat allergies).

  • Olfactory training may help recovery after viral illness.

  • Safety measures: install smoke/gas detectors, check food expiry dates.

  • Seek medical review if anosmia is persistent, sudden without cold, or associated with neurological symptoms.




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