34.1 A Stepwise Assessment

• History

Onset, timing, duration, associated symptoms

Listen carefully to details of actual complaint—smell, “taste,” true taste, distortion

If distortions present, do they coincide with a stimulus?

Original precipitating factor?

Other specific nasal or oral symptoms?

• Examination

Rigid endoscopy of the nose with a 30° scope to visualize olfactory clefts

Examination of the tongue, oral cavity and oropharynx ± hypopharynx

• Psychophysical testing—consider birhinal testing

• Further investigations:

Blood tests—LFTs, TFTs, 9 AM cortisol, U&Es, ESR, ANCA, TPHA/VRDL, HbA₁C

For taste consider B₁₂, folate, Mg/Ca/Zn levels

MRI—if normal endoscopy or in unilateral olfactory/taste dysfunction

CT—if positive endoscopic findings or history suggestive of possible inflammatory sinonasal disease

34.2 Psychophysical Testing

34.2.1 Olfactory Testing

• Should be considered first unless clear history of specific taste modality losses

• Sniffin’ Sticks—threshold, discrimination and identification (international validation including UK)

• Combined olfactory test—threshold and identification (United Kingdom/New Zealand validated)

• UPSIT—identification only (international validation, especially North America)

• CCCRT—threshold and identification

• Smell diskettes—identification

• BAST-24

• Others include: Leicester olfactometer (threshold), Japanese odour pens, European Smell Test

• Retronasal testing—for flavor perception via the retronasal route

• Malingering not ruled out by ammonia test due to olfactory/trigeminal interactions centrally; should be suspected with very low scores on testing (i.e., forcing a low score)

34.2.2 Gustatory Testing

• Taste test strips/sprays

34.2.3 Specialist Investigations

• Olfactory event-related potentials (OERPs)

EEG of olfaction typically with a pleasant and unpleasant odour

Duration of test = 30 to 40 min

If absent, suggest anosmia with bad prognosis but not absolute

If present, suggest patient can smell and has a good prognosis

• Gustatory event-related potentials—as for OERPs

• Functional MRI—with odour/taste stimulus

• Olfactory bulb volume measurement—derived from MRI

• Trigeminal testing—chemosensory event-related potentials—using CO₂ direct into the nose

• Olfactory/gustatory electrogram (research tool)

34.2.4 Olfactory Loss—Terminology Quantitative Loss

• Normosmia

• Hyposmia

• Anosmia

• Functional anosmia—ability to occasionally detect spurious olfactory sensations

• Presbyosmia—age-related decline (especially after 70 years)

• Olfactory agnosia—inability to detect and specify one odour

• Hyper/superosmia

Qualitative Loss

• Dysosmia—any distortion of the sense of smell