Olfactory nerve

Why Does the Olfactory Nerve Get No Respect?

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Pity the poor Olfactory Nerve.

Yes, Cranial Nerve I. The “ON” in the mnemonic chanted by first-year med students to recall the cranial nerves in neuroanatomy class.

 Apparently, this sensory modality is an obsolete vestige of our neurological heritage that lacks the cache of its 11 siblings.

And how do I reach this conclusion?

If you read through any typical medical chart (with or without EHR assistance), the common documentation reads “Cranial Nerves 2-12 were within normal limits.”

Ergo, the ability to smell has no clinical relevance.

However, a recent study published in Neurology looked at the olfactory capability of 231 servicemen who sustained polytrauma, blast exposure, and moderate to severe TBI using a standardized quantitative olfactory assessment and compared that clinical examination with the presence of orbitofrontal abnormalities on neuroradiographic studies. While the study’s intent was to reduce unnecessary use of neuroimaging, the key clinical pearl was that the presence of an abnormal quantitative olfaction score had low sensitivity, but high specificity (100% to be precise) for the presence of intracranial abnormalities on neuroimaging!

 The “take home message,” as I see it, is that assessment of smell in patients with suspected brain injury can provide critical information regarding structural damage intracranially. In my clinic, every new evaluation of a patient with a suspected TBI whether from sports, road traffic incident, or otherwise includes a brief olfactory assessment as follows:

1. Assessment of the patency of each nostril/nares by visual inspection with a nasal speculum followed by a functional assessment in which each nares is occluded and the air flow capacity is checked.

2. Five separate containers (I use old film canisters) containing four olfactory triggers (chocolate, coffee, peanut butter, cloves) and one trigeminal trigger (mint) to detect feigning are used.

3. With eyes closed and one nostril occluded, each smell canister is presented to the patient with the following prompt: “I will be presenting you with five different smells that are commonly found in a kitchen. Tell me if you smell anything and then, what that smell is as best you can.”

4. If the patient is unable to identify any of the smells (including the trigeminal trigger), that is an alert for the possibility of malingering.

5. If the patient states they smell something, but are unable to identify the odor, they are then given the five options to select from in a multiple choice format.

6. After each nostril has been evaluated, the patient is then queried to assess for a relative asymmetry in their ability to detect smells by the following prompts: “Was there a difference between the left and right sides in terms of the intensity of smell?

7. If so, which was stronger?” They are then asked to “quantify” the intensity as follows: Peanut butter (the most pure olfactory trigger) is presented to the “stronger” side and the patient is told “If this side (stronger) is a dollar’s worth of smell, how much is this side worth (when testing the “weaker” side)?” This gives a percentage estimation regarding left and right intensity that define hyposmia (reduced, but not absent, smell detection) or dysosmia (impaired sense of smell). Anosmia, unilateral or bilateral, is total loss of smell.

Finally, several clinical “pearls” to keep in mind:

Patients with unilateral abnormalities in olfactory function most typically complain of altered sense of taste or the increased use of spices, peppers, etc as 70% of what we experience as “flavor” is really the aroma of the meal. (eg., Consider how food tastes bland when one has a coryzal syndrome and airways are blocked.)

The patient’s family may be the first to complain that the food cooked by the patient is too spicy!

Patients with a history of GERD may present with an increase in their symptoms or nocturnal reflux due to excessive seasoning.

Many mild TBI patients based on Glasgow Coma Score criteria (13-15) will actually be moderate in severity if one inquires regarding the duration of post-traumatic amnesia (moderate defined as >24 hours of impaired memory function).

If You Can Smell This, You May Not Have Alzheimer’s.

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A new diagnostic test involves a dollop of peanut butter.

Peanut Butter

You may not have heard of “the peanut butter test,” but it could become a fantastically low-cost and non-invasive way to test for Alzheimer’s. After all, what’s less invasive than asking someone to smell some delicious peanut butter?

“The ability to smell is associated with the first cranial nerve and is often one of the first things to be affected in cognitive decline,” reads this release from the University of Florida, researchers from which conducted the experiment. But with Alzheimer’s patients, the sense of smell is affected in a very particular way: The left nostril is significantly more impaired than the right. Weird! But true.

The experiment involved capping one nostril and measuring the distance at which the patient could detect about a tablespoon of peanut butter. In Alzheimer’s patients, the left nostril was impaired so thoroughly that, on average, it had 10 centimeters less range than the right, in terms of odor detection. That’s specific to Alzheimer’s patients; neither control patients (those not suffering from cognitive decline) nor those with other types of cognitive impairment (like dementia) demonstrated that nostril difference.

Peanut butter was used because it’s a so-called “pure odorant.” Generally our sense of smell actually incorporates two distinct sensations: the olfactory sense, or smell, as well as a trigeminal sense, which is like a more physical burning or stinging sort of sense. Peanut butter has no trigeminal element; it’s only olfactory, which makes it ideal for testing, as the link to Alzheimer’s is specifically dealing with the olfactory sense.

This could be a great, inexpensive, early warning system for those with Alzheimer’s; the illness is not easy to detect, requiring neurological examination as well as mental, and has to be carried out by a professional. The peanut butter test? Much easier.