Olfactory Disorders

Olfactory Disorders

Olfactory Disorders

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Olfactory Pathway - Nose Knows How

  • Olfactory Epithelium: Located in the nasal cavity roof, superior septum & superior concha.
    • Cell Types:
      • Olfactory Receptor Neurons (ORNs): Bipolar neurons; site of odor detection.
      • Basal Cells: Stem cells; responsible for regenerating ORNs.
      • Sustentacular Cells: Provide structural and metabolic support.
  • Odorant Reception Mechanism:
    • Odorants dissolve in mucus, bind to Odorant Binding Proteins (OBPs).
    • OBP-odorant complex activates G-protein coupled receptors (GPCRs, specifically Golf) on ORN cilia.
    • Signal Transduction: ↑cAMP → opens ion channels → depolarization → action potential.
  • Central Olfactory Pathway: 📌 CN I
    • ORN axons (unmyelinated) pass through cribriform plate, synapse in Olfactory Bulb (glomeruli).
    • Olfactory Tract projects to Primary Olfactory Cortex (bypasses thalamus initially):
      • Piriform cortex (main olfactory discrimination)
      • Amygdala (emotional response to odors)
      • Entorhinal cortex (olfactory memory) Olfactory Pathway Anatomy: Epithelium to Cortex

⭐ Olfactory receptor neurons are unique as they are bipolar neurons that regenerate throughout life (approximately every 30-60 days).

Smell Saboteurs - Types & Triggers

  • Classification of Olfactory Disorders:

    • Anosmia: Total smell loss.
    • Hyposmia: Reduced smell.
    • Hyperosmia: Heightened smell.
    • Dysosmia: Distorted smell perception.
      • Parosmia: Misperception of an odor (e.g., pleasant odor perceived as foul).
      • Phantosmia: Olfactory hallucination (perception of odor when none is present).
    • Agnosia: Inability to identify or classify odors, despite intact smell detection.
  • Etiology: Conductive vs. Sensorineural Loss

    TypeMechanismExamples
    ConductiveImpaired airflow to olfactory epitheliumNasal polyps, rhinitis (allergic/viral), septal deviation, tumors.
    SensorineuralDamage to neuroepithelium/olfactory pathwaysViral URI, head trauma, neurodegenerative (Parkinson's, Alzheimer's), toxins, congenital (Kallmann syndrome).
  • Major Etiological Categories:

⭐ Upper Respiratory Tract Infection (URTI) is the most common cause of persistent olfactory loss in adults.

Sniff Sleuth - Testing Smells

  • Clinical Approach:
    • History: Detail onset, duration, severity (anosmia/hyposmia), associated symptoms (nasal obstruction, rhinorrhea, neurological deficits), history of URTI, head trauma, toxin exposure.
    • Examination: Nasal endoscopy for sinonasal pathology (polyps, inflammation); focused neurological exam (esp. CN I).
  • Psychophysical Smell Tests: Standardized objective evaluation.
    • Qualitative: Basic identification of common familiar odors (e.g., coffee, soap).
    • Quantitative:
      • UPSIT (University of Pennsylvania Smell Identification Test): 40-item "scratch-and-sniff" forced-choice booklet. Scoring norms available.

        ⭐ The University of Pennsylvania Smell Identification Test (UPSIT) is a widely used 40-item scratch-and-sniff test.

      • Sniffin' Sticks: Pen-like devices testing Odor Threshold, Discrimination, and Identification (TDI score).
  • Imaging Studies:
    • CT Sinuses: Indicated for suspected sinonasal disease (e.g., CRS, tumors).
    • MRI Brain/Olfactory Bulb: For suspected central causes or unexplained olfactory loss.

UPSIT smell identification test kit

Specific Disorders & Management - Scent Setbacks

DisorderKey Management StrategyPrognostic Factor
Post-Viral Olfactory Dysfunction (PVOD)Olfactory training; Corticosteroids (oral/topical - limited long-term evidence)Variable; training response
Post-Traumatic Olfactory DysfunctionOlfactory trainingVariable
Sinonasal Disease-relatedTreat underlying cause (e.g., surgery for polyps, medical therapy for rhinosinusitis)Depends on cause resolution
Neurodegenerative (Parkinson's, Alz.)Symptomatic; No specific cure for olfactory lossPoor for olfactory recovery
Congenital Anosmia (Kallmann Syn.)Genetic counseling; Hormone replacement (if indicated)Generally poor for olfaction

High‑Yield Points - ⚡ Biggest Takeaways

  • Anosmia is the complete loss of smell; hyposmia is reduced smell.
  • Most common cause of anosmia/hyposmia is viral URI, followed by head trauma.
  • Kallmann syndrome: congenital anosmia with hypogonadotropic hypogonadism.
  • Olfactory neuroblastoma (esthesioneuroblastoma) from olfactory epithelium; presents with nasal obstruction, epistaxis.
  • COVID-19 is a significant cause of sudden onset anosmia/hyposmia.
  • Zinc deficiency can cause olfactory dysfunction.
  • Olfactory groove meningiomas can cause anosmia by compressing olfactory nerves_

Practice Questions: Olfactory Disorders

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A child is brought to the paediatric OPD with fever of 24 hours duration. History reveals 3 episodes of chest infection and passage of foul smelling stools. The most probable diagnosis is-

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Flashcards: Olfactory Disorders

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In adenoid hypertrophy voice is toneless and loses nasal quality due to nasal obstruction i.e. rhinolalia _____.

TAP TO REVEAL ANSWER

In adenoid hypertrophy voice is toneless and loses nasal quality due to nasal obstruction i.e. rhinolalia _____.

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