Cranial Nerve I: Olfactory Nerve

Published on 09/04/2015 by admin

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Last modified 22/04/2025

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Cranial Nerve I

Olfactory Nerve

This is rarely tested in clinical practice.

Examination is usually performed to investigate a specific complaint rather than as a screening test. Most recognisable smells require olfaction. Some agents such as ammonia can be recognised by the nasal epithelium and do not require an intact olfactory pathway.

WHAT TO DO

• Very simple: Ask the patient if they have noticed a change in their sense of smell (this is really history rather than examination).

• Simple: Take a bedside object—a piece of fruit, an orange, a juice bottle—and ask the patient if it smells normal.

• Formal: A selection of substances with identifiable smells in similar bottles is used. Agents often used include peppermint, camphor and rosewater. The subject is asked to identify these smells. An agent such as ammonia is usually included. Each nostril is tested separately.

WHAT YOU FIND

• The patient is able to identify smells appropriately: normal.

• The patient is unable to recognise scents offered but recognises ammonia: anosmia. This finding is limited to one nostril: unilateral anosmia.

• The patient recognises no smells, including ammonia: consider that the loss may not be entirely organic.

WHAT IT MEANS

• Anosmia in both nostrils: loss of sense of smell. Common causes: blocked nasal passages (e.g. common cold), trauma; a relative loss occurs with ageing and Parkinson’s disease.

• Unilateral anosmia: blocked nostril, unilateral frontal lesion (meningioma or glioma—extremely rare).

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Cranial Nerve I

Olfactory Nerve

This is rarely tested in clinical practice.

Examination is usually performed to investigate a specific complaint rather than as a screening test. Most recognisable smells require olfaction. Some agents such as ammonia can be recognised by the nasal epithelium and do not require an intact olfactory pathway.

WHAT TO DO

• Very simple: Ask the patient if they have noticed a change in their sense of smell (this is really history rather than examination).

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