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Tests of Olfaction - ENT PG Answer

Definition of Terms

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Classification of Olfactory Tests

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A. Subjective / Psychophysical Tests

1. Bedside / Simple Tests

• Open an isopropyl alcohol packet; hold it at progressively closer distances (starting ~30 cm, moving 1 cm closer with each expiration)
• Normal: detection at ~30 cm
• Anosmic patients may still feel trigeminal irritation (CN V) when the packet is very close to the nose - this must be distinguished from true olfactory detection

• Contains 3 common odors embedded in microencapsulated strips
• Quick bedside screening tool

2. Standardized Psychophysical Test Batteries

University of Pennsylvania Smell Identification Test (UPSIT) - MOST IMPORTANT FOR PG EXAMS

• Self-administered, 40-item, scratch-and-sniff, multiple-choice test
• Scored out of 40
• Most widely used clinical test worldwide
• High test-retest reliability
• Adjusted for age and gender
• Scoring interpretation:

• Detecting malingerers: Score ≤5 indicates fewer correct answers than expected by chance (each question has 4 options, so chance alone gives ~10 correct). Malingering is confirmed by presenting a strong CN V stimulant like ammonia - a truly anosmic patient will still react to ammonia (trigeminal response), while a malingerer claiming total insensitivity may not react at all.

Sniffin' Sticks (TDI Test)

• Reusable felt-tip odor-producing pens (examiner-administered)
• Pen placed 2 cm from nostril
• Tests three components:
  • T - Odor Threshold (using n-butanol dilutions, forced-choice)
  • D - Discrimination (pick odd odor from trio)
  • I - Identification (name the odor from 4 options)
• Composite TDI score used for diagnosis
• Validated in multiple countries and in children
• Clinical significance: Sinonasal dysfunction - mainly impaired threshold scores; Parkinson's disease - mainly impaired suprathreshold (discrimination/identification) scores

Connecticut Chemosensory Clinical Research Center (CCCRC) Test

• Tests both butanol threshold (olfactory) and identification
• Uses a stepwise forced-choice procedure

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B. Objective / Electrophysiological Tests

• OERPs are the most objective way to detect malingering or assess suspected non-organic anosmia
• Adams & Victor notes: "These are essentially research tools and not used in routine neurological practice"

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C. Retronasal Olfaction Testing

• Flavored powders placed in the mouth with nares closed
• Tests the retronasal (posterior) olfactory route
• Useful in post-head-injury cases: both orthonasal and retronasal function decline simultaneously
• In sinonasal disease: orthonasal route affected preferentially, retronasal may be preserved

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Flowchart 1: Approach to a Patient with Smell Complaint

Patient with Smell Complaint
         │
         ▼
  Clinical History
  (onset, duration, prior URI, trauma, medications, smoking)
         │
         ▼
  Anterior Rhinoscopy / Nasal Endoscopy
         │
    ┌────┴────────────────────┐
    │                         │
Nasal pathology seen    No nasal pathology
(polyps, sinusitis)          │
    │                    ▼
    ▼             Psychophysical Testing
CT Paranasal Sinuses     (UPSIT / Sniffin' Sticks)
    │                         │
    ▼                  ┌──────┴──────┐
Treat sinonasal      Hyposmia    Anosmia
disease           /microsmia       │
                      │         Check score ≤5?
                      │           Yes → Suspect malingering
                      ▼           → OERP / Ammonia (CN V) test
                   MRI Brain
            (olfactory bulbs/tracts,
             frontal lobe, tumor)

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Flowchart 2: UPSIT Score Interpretation

UPSIT Score (out of 40)
         │
    ┌────┴────────────────────────────────────┐
    │         │           │                   │
  35-40     19-34        6-18                ≤5
    │         │           │                   │
 NORMAL    HYPOSMIA   ANOSMIA         MALINGERING
            (mild to                   Ammonia (CN V) test
             severe)                   OERP for confirmation

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Flowchart 3: Sniffin' Sticks TDI Pattern and Etiology

Sniffin' Sticks - TDI Score
         │
    ┌────┴──────────────────────┐
    │                           │
Threshold mainly impaired   Discrimination/Identification
(T score low)               mainly impaired (D+I score low)
    │                           │
    ▼                           ▼
Sinonasal cause            Neurodegenerative cause
(CRS, nasal polyps)        (Parkinson's disease,
                            Alzheimer's disease)

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Key PG Points to Remember

1. UPSIT - 40-item, scratch-and-sniff, self-administered, most widely used test
2. Score ≤5 = malingering (worse than chance in a 4-option test)
3. Sniffin' Sticks measure TDI (Threshold, Discrimination, Identification)
4. Alcohol sniff test - normal detection at ~30 cm
5. Ammonia tests CN V, not CN I - used to expose malingerers
6. OERP = objective test, gold standard for medicolegal anosmia
7. Retronasal olfaction tests flavor via the posterior route (mouth, nares closed)
8. Sinonasal disease - impaired threshold; Parkinson's - impaired identification
9. Age >65: >50% have significant olfactory decline
10. Top 3 causes of chronic smell loss: URI > Head trauma > Chronic rhinosinusitis

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