Examination of Olfactory Nerve (CN 1)

Smell, if tested, requires soft musks, floral and ketone smells rather than astringents, such as ammonia or cloves. The reason for this is that astringents are also noxious. They may stimulate trigeminal (CN V) nerve endings in the nose, causing perception of the stimulus even with completely severed CN 1. Each nostril is tested individually and not necessarily with a different scent, so that the patient is asked if the test scent is the same or different in each nostril. Often the patient will say they are different when they are the same, making interpretation difficult. A CN 1 palsy should alert the GP to the possibility of a meningioma of the olfactory groove. This is a slow growing tumour that may be ignored because its effects come on slowly. The patient may not be aware that they have lost the sense of smell. Loss of smell, associated with the flu, may be permanent. Sensation of smell and taste are intertwined so a patient complaining of altered taste
may be identifying problems with smell.