1st Cranial Nerve – Tests for the Olfactory Nerve

Definition:

The use and interpretation of physical examination techniques to determine the integrity and adequate function of the olfactory nerve (first cranial nerve). This nerve provides the innervation for one of the special senses: smell.

Test procedure:

Physical examination should involve rhinoscopy which may reveal polyps, membranous inflammation, foreign bodies, and septal deviations. A neurological examination should be performed with the aim of excluding any sinister pathologies and assess the proper functioning of the higher centres.

Radiographic studies should be reserved for specific indications such as fractures and intracranial lesions.

The most widely used quantitative clinical test is the University of Pennsylvania Smell Identification Test (UPSIT) which consists of four booklets containing ten micro-encapsulated odours in a straight-forward “scratch-and-sniff” format.

Test findings (inc Positive & Negative results):

 Olfactory lesions may be sub-divided into the following categories: a) anosmia: inability to appreciate qualitative olfactory sensations, b) partial anosmia: the ability to appreciate some but not all odorants, c) microsomia or hyposmia: reduced sensitivity to odorants d) hyperosmia: pathologically acute sense of smell, e) dysosmia, cacosmia, or parosmia: altered/distorted sense of smell, f) phantosmia: an olfactory hallucination, and g) olfactory agnosia: the inability to interpret an odorant.

The test results will help determine which kind of olfactory defect the patient is suffering from, and influence the type of further investigation, if warranted.

Considerations:

Head trauma, toxic exposure, smoking history, sinonasal diseases, rhinoplasty, and upper respiratory tract infections should be considered as differentials.

Certain medications such as antifungal agents and angiotensin-converting enzyme inhibitors have been known to influence olfaction. Conditions such as epilepsy, multiple sclerosis, Parkinson’s disease, and Alzheimer’s disease are also associated with olfactory nerve lesions.