Most providers start the cranial nerve screen with CNII, but that has been changing since COVID-19 entered the scene. The primary presenting symptoms of loss of taste and smell have re-anchored the sensory systems in the neurological screening and the cranial nerve exam. Both smell and taste are transmitted via cranial nerves so this screening is becoming all the more important in identifying patients with mild cases of COVID-19 in outpatient settings.
Remember the story I told about the patient with a shearing injury to her brain? In clinical practice, the cranial nerve screen is a standard part of my Neuro Screen, which you can check out HERE! In every patient I see who has a complex disease presentation or any risk factors for underlying neurological conditions, (let’s be real, that’s everyone I see) I do this screening and include a cranial nerve screen as well.
Specifically for patients with advanced diabetes, several balance issues can be related to visual disturbances resulting from calcified arterial supply to the cranial nerves. You’ll find these when you do a good cranial nerve exam. And for patients with BPPV, a vestibular condition happening at increased frequency in patients with COVID-19, checking those cranial nerves is a necessary portion of your evaluation.
Here is the quick screening version:
CN I: Smell – have them smell something… your choice here… Probably one of the more important tests these days, so don’t skip it like we used to. As people age, their sense of smell can severely decrease, leading to changes in their ability to enjoy or crave food. Smell is a primary factor in nutrition. See the whole patient.
CN II: Optic – have them give you the color of something or read your name badge or count your fingers (you’ll have to accommodate those who are color blind, who cannot read, or who have aphasias). You can also test peripheral vision here.
CN III: Oculomotor – have them follow your finger with only their eyes, draw a capital “X” with a strike-through horizontal line (
X). Then make sure to move your finger in a circle in both directions. Look for saccadic or abnormal eye movements, nystagmus, or strabismus. These can be a sign of decompensated or mismanaged chronic health conditions like diabetes.
My little trick for this one: LR6(SO4)3 . I was a chemistry minor in college so this worked for me, but it basically means that the Lateral Rectus is innervated by CN VI, Superior Oblique is innervated by CN IV, and all the other oculomotor nerves are CN III. So you get three tests in one here.
CN IV: Trochlear – see CN III, tested together. The downward part of drawing the letter X. Drawing the circle gives you Superior Oblique.
CN V: Trigeminal – supplies sensory to the face and comes in three branches (ophthalmic, maxillary, and mandibular). Make sure to check all three regions. The trigeminal nerve also supplies motor input to the pterygoids, so you can have the patient clench their jaw and palpate contraction.
CN VI: Abducens – see CN III, tested together. The horizontal bar across the letter X.
CN VII: Facial – supplies motor input to the face and comes in five branches (temporal, zygomatic, buccal, mandibular, and cervical). Make sure to assess all five branches of motor control using facial expression. Typical facial expressions are eyebrow elevation/forehead wrinkle, puff out cheeks, big smile, purse lips, and close eyes tightly. You can also test taste on the anterior 2/3 of the tongue, especially if screening for COVID-19.
CN VIII: Vestibulocochlear – In the absence of a tuning fork, this is typically tested by gently rubbing fingers together near the patient’s ears and asking if they hear anything, however, this is highly subjective.
CN IX and X: Glossopharyngeal and Vagus – have the patient open their mouth a say “ah”, observe for uvula deviation. Ensure the palate is rising symmetrically and that air is not escaping through the nose. You can also observe your patient swallowing if you know what you’re looking for, or you can test taste on the posterior 1/3 of the tongue (maybe the test of choice if screening for COVID-19). Vagus nerve damage at any point along the nerve including the root within the brain can also result in blood pressure fluctuations (see the case I mentioned above).
CN XI: Accessory – controls the motor to the spinal accessory muscles. Have the patient elevate both shoulders and hold against resistance.
CN XII: Hypoglossal – have the patient stick their tongue out and observe for midline positioning.
So, there are the easy ways to do the screen, making it easier for you to quickly fit it in amongst all the other things you need to do. Setting that baseline is so important so that, when things change, because they will, you have something to compare it to!
How often do you do a cranial nerve screen? Drop a number in the comments!
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The contents of this blog and all associated pages reflect the opinions of the author and should not be construed as medical advice. Please consult your doctor for medical advice.
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