Cranial Nerve Exam

examining the CNs allows for examination of what brain structure?

-brainstem

abnormalities of a CN exam can possibly be traced back to what origins?

-CNS pathways to & from cortex, diencephalon, cerebellum, or other parts of brainstem

-lesions in nucleus

-lesions in nerve

-generalized dysfunction of nerve, NMJ, or muscles

what equipment is needed for the CN exam?

-nasal speculum

-2 non-irritating scents

-ophthalmoscope

-pocket Snellen/Rosenbaum charts

-color vision assessment cards

-eye cover or notecard

-cotton wisp

-broken tongue blade

-512Hz tuning fork

-sterile tongue blade

how is CN I typically assessed clinically?

-during medical Hx

what is the test for CN I?

-test ability to identify familiar odors 1 naris at a time

what is the technique for assessing CN I?

-check patency of each naris → instruct patient to close eyes → have patient occlude R naris & hold scent #1 under nostril → ask patient to inhale & identify odor → repeat with other naris & scent #2

what is parosmia?

-distorted odor perception triggered by a stimulus

what is phantosmia?

-olfactory hallucination

what are screening tools for the assessment of CN I?

-Self-Reported Mini Olfactory Questionnaire (Self-MOQ)

-Brief & Full Questionnaire of Olfactory Disorders

what is the most common cause of olfactory dysfunction?

-sinonasal conditions

what are the PE findings that are suggestive of sinonasal pathology?

-intranasal mass

-edematous mucosa

-hypertrophy of turbinates

-purulent mucus

-bleeding

what are less common causes of olfactory dysfunction?

-medications/toxins

-structural pathology

-nutritional deficiencies

-post-radiation to the head/neck

-endocrine disorders

-psychiatric conditions

what nutritional deficiencies are associated with olfactory dysfunction?

-pernicious anemia

-vitamin B12 deficiency

-vitamin A deficiency

-niacin deficiency

what endocrine disorders are associated with olfactory dysfunction?

-hypothyroidism

-Addison’s disease

-pregnancy

what psychiatric conditions are associated with olfactory dysfunction?

-schizophrenia

-major depressive disorder

-anorexia nervosa

what is presbyosmia? what Hx clues should you look for?

-age-related loss of olfactory neurons that leads to reduced olfactory cortex activity

-insidious onset w/o improvements

what neurodegenerative disorders are associated with olfactory dysfunction? what Hx clues should you look for?

-Alzheimer’s disease, Parkinson’s disease

-insidious onset w/o improvements

how is CN II tested?

-vision assessment

what components of the visual exam are used to evaluate CN II?

-central visual acuity = near & distance vision

-color vision

-peripheral vision (visual fields with confrontation testing)

-pupillary light reflex

-fundoscopic exam

-pupil assessment

-pupillary responses to light & accommodation

testing a patient’s pupillary light reflex evaluates the function of what CNs?

-II

-III

assessing a patient’s pupil appearance & responses to light/accommodation are performed to evaluate the function of what CNs?

-II

-III

why would you perform the swinging flashlight test?

-to assess for afferent pupillary defect

what is a Marcus-Gunn pupil? is this associated with a CN? if so, which?

-deafferented pupils (NO anisocoria) that constrict to consensual but not direct light

-yes → CN II

what is a Hutchinson pupil? is this associated with a CN? if so, which?

-dilated pupil demonstrating anisocoria that doesn’t respond to direct or consensual light

-yes → CN III

what pupillary defect is caused by a lesion of CN II?

-Marcus-Gunn pupil

what pupillary defect is caused by a lesion of CN III?

-Hutchinson pupil

what is Horner’s syndrome? is this associated with a CN? if so, which?

-constricted pupil demonstrated anisocoria with associated ptosis & decreased facial sweating

-no → caused by dysfunctional sympathetics

what is an Adie’s Tonic pupil? is this associated with a CN? if so, which?

-dilated pupil demonstrating anisocoria with an impaired light response & slow constriction with accommodation

-no → caused by dysfunction of parasympathetics

what is an Argyll Robinson pupil? is this associated with a CN? if so, which?

-constricted irregular pupil (w/o anisocoria) that constricts with accommodation but not light

-no → caused by dysfunction of pretectum

what 3 CNs are grouped together in a PE assessment?

-III, IV, & VI

how are CNs III, IV, & VI tested?

-assessment of EOMs & movement of upper eyelid

what components of the visual exam are used to evaluate CNs III, IV, & VI?

-visual inspection of upper eyelids

-visual inspection of ocular alignment via corneal light reflex

-6 cardinal directions of gaze

-other eye movements to test image fixation on the retina = smooth pursuits, VOR, saccades

-visual inspection for nystagmus

how is ptosis clinically defined? how is the severity defined?

-distance between upper lid margin & light reflex > 2mm

-mild = 2mm droop

-moderate = 3mm droop

-severe = 4+ mm droop

what is the vestibulo-ocular reflex?

-oculocephalic/Doll’s eyes reflex that assesses image fixation on the retina

what is saccades?

-redirection of line-of-sight to test eye movements

which CN controls the superior oblique muscle?

-CN IV

which CN controls the lateral rectus muscle?

-CN VI

which CN controls eyelid elevation?

-CN III

which CN controls pupillary responses?

-CN III

what are the classifications of CN III palsy?

-isolated

• pupil-sparing

• nonpupil-sparing

-non-isolated

what causes a nonpupil sparing isolated CN III palsy?

-complete lesion that leads to full internal & external CN III dysfunction

what causes a pupil-sparing isolated CN III palsy?

-partial lesion that causes some internal &/or external CN III dysfunction

what are the internal & external functions of CN III?

-internal = pupil size, responses to light, accommodation

-external = eyelid strength/position, EOM innervation

how can you determine which CN III functions are impaired in a pupil-sparing isolated CN III palsy?

-normal pupil size & reactivity = no internal dysfunction

-dilated, poorly reactive pupil = partial internal dysfunction

-dilated pupil that is non-reactive to light & accommodation = full internal dysfunction

-intact EOMs w/o ptosis = no external dysfunction

-partially impaired EOMs &/or ptosis = partial external dysfunction

-completely impaired EOMs & ptosis = full external dysfunction

what EOM actions are controlled by CN III?

-ipsilateral adduction (medial rectus)

-elevation (superior rectus & inferior oblique)

-depression (inferior rectus)

what are the common etiologies of CN III palsy?

-structural lesions

-cerebrovascular dz = intracranial aneurysms, ischemia, CVA

-inflammatory/infectious = meningitis

-trauma

how does a CN III palsy typically present?

-sudden onset of binocular, vertical, or oblique diplopia

-eye pain

-headache

-ptosis

-mydriasis

-no pupil reactivity

-paralysis of adduction, elevation, & depression → eye rests in “down & out” position OR weakness in actions

what are the PE findings of a CN III palsy?

-mydriasis

-unreactive pupil

-ptosis

-paralysis of weakness of adduction, elevation, & depression → resting eye position that is “down & out”

what are the classifications of CN IV palsy?

-congenital

-acquired

-isolated

-non-isolated

what are common causes of CN IV palsy?

-congenital

-trauma

-microvascular dz

how does CN IV palsy typically present?

-binocular vertical diplopia

-compensatory head turn/tilt

how is a CN IV palsy diagnosed on PE?

-Parks-Bielschowsky 3-step test

why would you use the Parks-Bielschowsky 3-step test?

-to diagnose CN IV palsy

what is the most common CN palsy to occur in isolation?

-CN VI

what are common causes of a CN VI palsy?

-tumor

-trauma

-vascular dz

how does a CN VI palsy typically present?

-binocular horizontal diplopia

-eye pain

-compensatory head turn/eye closure

-medial drift of affected eye when looking straight ahead

-deviation more obvious with R/L gaze

how can you differentiate between a CN IV & CN VI palsy?

-IV = binocular vertical diplopia

-VI = binocular horizontal diplopia

which CN palsy involves ptosis?

-CN III

what CN provides primary facial sensory innervation?

-CN V

what is the motor innervation of CN V?

-temporalis muscles

-masseter muscles

how is CN V tested?

-assess light touch & superficial pain in all 3 branches

-strength testing of temporalis & masseter muscles

-assess corneal reflex

what are the 3 branches of CN V?

-temporal

-maxillary

-mandibular

what condition is also known as tic doulourex?

-trigeminal neuralgia

what is trigeminal neuralgia?

-rare condition that causes recurrent brief episodes of unilateral electric shock-like pains that abruptly begin & end when triggered by innocuous stimuli in the distribution of 1+ trigeminal branches

what is the diagnostic criteria for trigeminal neuralgia?

-a: recurrent episodes of unilateral facial pain in proper distribution

-b: pain lasts from a second-2min, is severe, & has electric shock-like, shooting, stabbing, or sharp qualities

-c: precipitated by innocuous stimuli

-d: no better Dx

what CNs are evaluated when assessing the corneal reflex?

-CN V (trigeminal)

-CN VII (facial)

when would you assess a patient’s corneal reflex to evaluate CN functionality?

-patients in stupor/coma

-objective assessment of ophthalmic branch “numbness”

the corneal reflex may be absent in what patient demographic?

-contact wearers

what are the motor & sensory functions of CN VII?

-motor = primary muscles for facial expression & corneal reflex

-sensory = anterior 2/3 of tongue (taste)

how is CN VII tested?

-motor = have patient demonstrate facial expressions (raise eyebrows, puff out cheeks, smile with teeth, smile w/o teeth)

-strength = pull up on upper eyelids while having patient try & close eyes

-sensory = not routine

what is the expected dysfunction of CN VII with UMN pathology?

-inability to close contralateral eye

-inability to raise contralateral corner of mouth

what is the expected dysfunction of CN VII with LMN pathology?

-Bell’s palsy

what is the UMN distribution of CN VII?

-R & L LMN for moving forehead up/down

-contralateral LMN for lower face movement

what is Bell’s palsy?

-LMN dysfunction of CN VII that causes sudden paralysis/weakness of ipsilateral facial muscles

what are the hallmark features of Bell’s palsy?

-loss of forehead wrinkles

-inability to close contralateral eye

-inability to raise contralateral corner of mouth

-decreased naso-labial prominence of contralateral side

how is dysfunction of CN VII graded?

-House-Brackmann FN Grading system

what are the grades of the House-Brackmann FN Grading System?

-I = normal facial function in all areas

-II (mild) = mild weakness, mild synkinesis, & complete eyelid closure with minimal effort

-III (moderate) = obvious, non-disfiguring facial asymmetry, noticeable but moderate synkinesis, hemifacial spasm/contracture, complete eyelid closure with effort, mildly weak mouth with maximal effort

-IV (moderately severe) = disfiguring facial asymmetry, facial weakness, inability to move forehead, incomplete eyelid closure, asymmetric mouth despite maximal effort

-V (severe) = minimal barely noticeable facial movement, asymmetric facial appearance, inability to move forehead, incomplete eyelid closure, minimal movement of mouth

-VI (total) = no facial movement

what are possible complications of CN VII dysfunction?

-permanent facial weakness

-blindness due to corneal injury

-contractures

-synkinesia

which CN is responsible for hearing & balance?

-CN VIII

how is CN VIII tested?

-hearing assessment = conversational, finger rub, Weber, Rinne

-vestibular function = balance assessment (gait, Romberg), nystagmus observation at rest & with Dix-Hallpike maneuver, caloric testing

what is the normal result of the Rinne test? what result indicates conductive hearing loss? sensorineural hearing loss?

-AC > BC by at least 2:1

-conductive = BC > AC

-sensorineural = AC > BC but < 2:1

what is the normal result of the Weber test? what result indicates conductive hearing loss? sensorineural hearing loss?

-no lateralization

-conductive = lateralization to deaf ear

-sensorineural = lateralization to good ear

how is the Dix-Hallpike maneuver performed?

-have patient sit with head turned 45* & eyes wide open → help patient lean back with 1 ear pointed to ground & hold position for 1-2min → while in position, check eyes for nystagmus

how is caloric testing performed?

-inject cold H2O into 1 ear while watching eyes for nystagmus

what are the 2 main types of nystagmus?

-jerk

-pendular

what is jerk nystagmus?

-alternating phases of a slow drift in 1 direction with a corrective quick “jerk” in the opposite direction

which type of nystagmus has a fast & slow component?

-jerk

how is jerk nystagmus classified?

-by trajectory (downbeat, upbeat, horizontal, torsional) OR by evoking factor (gaze-evoked, positional)

what is pendular nystagmus?

-slow sinusoidal, “pendular” oscillations to & fro

what are pathologic causes of nystagmus?

-vestibular lesions

-cerebellar lesions

-brainstem lesions

-drugs

-congenital

what are pathologic causes of nystagmus?

-end-gaze

-heights

-optokinetic

what are the symptoms commonly associated with nystagmus?

-vertigo

-oscillopsia

-blurred vision

-abnormal head positions

-imbalance

what is the most common symptom associated with nystagmus?

-vertigo

how can you differentiate between central & peripheral nystagmus with the Dix-Hallpike maneuver?

-peripheral

• latency period before nystagmus = 2-20s

• nystagmus for < 1min

• fatigability

• unidirectional nystagmus

• severe vertigo

• 1 position elicits vertigo

• vestibular paresis exhibited with caloric & rotary testing

-central

• no latency period before nystagmus

• nystagmus for > 1min

• no fatigability

• nystagmus may be multidirectional

• minimal vertigo

• 2+ positions elicit vertigo

• hyperactive responses, impaired fixation, & suppression exhibited with caloric & rotary testing

what is the function of CN IX?

-sensation to posterior pharynx & larynx

what is the function of CN X?

-motor innervation of soft palate, pharyngeal muscles, & vocal cords

how are CNs IX & X tested?

-have patient open mouth → use tongue blade & light, have patient say “ahhh” → observe for elevation of soft palate & uvula

-elicit gag reflex

dysfunction of CN IX causes what?

-ipsilateral deviation of uvula

what is the function of CN XI?

-motor innervation of trapezius & SCM muscles

how is CN XI tested?

-assessment of SCM strength → resisted cervical rotation to R & L

-assessment of trapezius strength → resisted shoulder shrug