Physiology-Cranial Nerve Deficits Flashcards
A 24 year old female presents to the clinic 2 years after a 5 day episode of painful, blurry vision in her left eye that was treated with a course of steroids. MRI from 2 years ago is shown below. How would you expect her physical exam to go at the appointment today?
This patient had a bout of optic neuritis, seen in the MRI. The CN II neuritis causes damage to visual acuity, red desaturation (shown below), diminished pupillary constriction, a pale and atrophied optic disc.
What physical exam findings are typical of acute optic neuritis?
Swollen optic disc, enlarged blind spot and afferent pupillary defect (shine light in bad eye, stimulus travels to Eddinger-Westphal nucleus, stimulus not large enough to cause CN III-mediated contraction of good pupil)
What could be causing a patient to see his watch this way?
Monocular horizontal diplopia: retinal tears, vitreous humor. Binocular horizontal diplopia: neurological.
A patient presents to your clinic with horizontal diplopia. Physical exam reveals maximal diplopia on left endgaze while assessing smooth pursuits (avoiding saccade). When the patient coverers his left eye, the image at the left endgaze disappears. Which eye is the weak eye in this patient?
The right eye, this is because it is unable to swing over further to put the left endgaze image onto the fovea when the left eye is covered.
A patient presents with diplopia, difficulty walking down steps and reading. Images appear slightly side by side and mostly one on top of the other. You decide to do a Parks-Bielschowky three-step test. How do you do this?
1) Which eye is hypertropic on forward gaze? His left eye. Cross out muscles not involved pulling the left eye down or right eye up (RSO, RIR, LSR, LIO) 2) Which endgaze has worse diplopia? Right endgaze. Cross out muscles not involved in right endgaze (RIO, LIR). 3) Which direction is head tilt worse? Left. Circle muscle involved (LSO).
Why do patients with cranial nerve IV palsy have difficulty walking down stairs? How do they compensate?
When you walk down stairs the eyes have to look down and in, really difficult for an impaired superior oblique to do. Patients compensate by tilting their head opposite the affected side, the good eye will in tort and elevate to line up with the affected eye.
How high up CN IV do you need to go to get contralateral symptoms from the side of the lesion?
Basically to the brainstem, it crosses as soon as it comes out of the brainstem.
A patient presents to the clinic 2 years after having internuclear opthalmoplegia. How will his eye exam differ today from when he came in with acute symptoms 2 years ago?
Acute INO causes a lesion in the MLF. When the patient looks to the side, lateral rectus will fire because the FEF (frontal eye field) goes to CN VI nucleus and then CN VI goes straight to the lateral rectus. However, CN VI also sends a signal to CN IV nucleus via the MLF to get medial rectus to fire. Lesions in the MLF will cause that eye to remain forward facing. In a patient with a chronic MLF lesion, the brain will compensate & CN IV will cause medial rectus to fire, however the patient will have a unilateral nystagmus in the eye firing lateral rectus (CN VI).
A patient presents with double vision, full ptosis and an enlarged pupil. What physical exam findings will you see in this patient?
Notice the eye is “down and out” when opened and she cannot keep it open on her own. Also note that the eye is dilated. This is CN III palsy. Pupillary constriction, convergence, and accommodation will not happen.
What is diabetes’ favorite cranial nerve palsy?
CN III. Diabetes causes ischemia of the inner fibers of CN III, sparing the pupillary fibers. This is why it is called pupil-sparing diabetes, only affect the motor function of CN III.
How do you treat patients with diabetic CN III palsy?
Control blood glucose and patch the eye.
A patient presents with pain under the mastoid process and angle of the left jaw. One hour later, the patient begins to have paralysis of the left side of the face causing dysarthria and difficulty drinking water. What physical exam techniques will you perform on this patient?
This sounds like Bell’s palsy (CN VII). In addition to facial expression muscles, you want to look at lacrimation of the eye on the affected side, taste and hyperacusis in the ear. Checking his forehead crease will let you know if he has a central (forehead not affected) vs. peripheral lesion (forehead affected)
What labs do you want to run if the patient presents with bilateral Bell’s Palsy symptoms?
Lyme’s disease
Where do you look for lesions when patients present with Bell’s palsy?
Ears, tongue and palate. Lesions present in these locations when patients have herpes zoster flare ups (Ramsay Hunt Syndrome).
