Why cranial nerve examination

Nystagmus may be rotary, vertical, or horizontal and may occur spontaneously, with gaze, or with head motion. When trying to differentiate central from peripheral causes of vertigo, the following guidelines are reliable and should be considered at the onset:.

There are no central causes of unilateral hearing loss because peripheral sensory input from the 2 ears is combined virtually instantaneously as the peripheral nerves enter the pons. There are no peripheral causes of CNS signs. If a CNS sign eg cerebellar ataxia appears at the same time as the vertigo, the localization is virtually certain to be central.

Evaluation of vertigo using nystagmus testing is particularly useful in the following situations:. If patients have acute vertigo during the examination, nystagmus is usually apparent during inspection. However, visual fixation can suppress nystagmus. Clues that help differentiate central from peripheral vertigo in these patients include the following:. If nystagmus is absent with visual fixation but present with Frenzel lenses, it is probably peripheral.

If nystagmus changes direction eg, from one side to the other when, for example, when the direction of gaze changes , it is probably central. However, absence of this finding does not exclude central causes. When evaluating patients with acute vestibular syndrome rapid onset of severe vertigo, nausea and vomiting, spontaneous nystagmus, and postural instability , the most important maneuver to help differentiate central vertigo from peripheral vertigo is the head thrust maneuver.

With the patient sitting, the examiner holds the patient's head and asks the patient to focus on an object, such as the examiner's nose. Normally, the eyes stay focused on the object via the vestibular ocular reflex.

Other findings are interpreted as follows:. If the eyes temporarily move away from the object and then a frontal corrective saccade returns the eyes to the object, nystagmus is probably peripheral eg, vestibular neuronitis.

The vestibular apparatus on one side is dysfunctional. The faster the head is turned, the more obvious is the corrective saccade. If the eyes stay focused on the object and there is no need for a corrective saccade, nystagmus is probably central eg, cerebellar stroke.

When vertigo is episodic and provoked by positional change, the Dix-Hallpike or Barany maneuver is done to test the for obstruction of the posterior semicircular canal with displaced otoconial crystals ie, for benign paroxysmal positional vertigo [BPPV].

In this maneuver, the patient sits upright on the examining table. Direction and duration of nystagmus and development of vertigo are noted. The patient is returned to an upright position, and the maneuver is repeated with rotation to the other side.

Nystagmus secondary to BPPV has the following nearly pathognomic characteristics:. Usually, vertical upward-beating nystagmus when the eyes are turned away from the affected ear and rotary nystagmus when the eyes are turned toward the affected ear.

In contrast, positional vertigo and nystagmus related to CNS dysfunction have no latency period and do not fatigue. The Epley canalith repositioning maneuver can be done for both sides to help confirm the diagnosis of BPPV. The 9th glossopharyngeal and 10th vagus cranial nerves are usually evaluated together. Whether the palate elevates symmetrically when the patient says "ah" is noted. If one side is paretic, the uvula is lifted away from the paretic side. The eyes should stay fixed on the object and turn in the opposite direction of the head movement.

Vergence Vergence eye movements occur when the eyes move simultaneously inward convergence or outward divergence in order to maintain the image on the fovea that is close up or far away. Most often convergence is tested as part of the near triad.

When a patient is asked to follow an object that is brought from a distance to the tip of their nose the eyes should converge, the pupil will constrict and the lens will round up accommodation. Cranial Nerve 5 - Sensory Test for both light touch cotton tip applicator and pain sharp object in the 3 sensory divisions forehead, cheek, and jaw of CN 5. The limbal junction of the cornea is lightly touched with a strand of cotton.

The patient is asked if they feel the touch as well as the examiner observing the reflex blink. Cranial Nerve 5 - Motor The motor division of CN 5 supplies the muscles of mastication temporalis, masseters, and pterygoids. Palpate the temporalis and masseter muscles as the patient bites down hard.

Then have the patient open their mouth and resist the examiner's attempt to close the mouth. If there is weakness of the pterygoids the jaw will deviate towards the side of the weakness.

The last test for this nerve is testing for a jaw jerk , which is a stretch reflex. Have the patient slightly open their mouth then place your finger on their chin and strike your finger with a reflex hammer. Normally there is no movement. If there is a jaw jerk it is said to be positive and this indicates an upper motor neuron lesion. Start from the top and work down. Have the patient wrinkle forehead frontalis muscle , close eyes tight orbicularis oculi show their teeth buccinator , and purse lips or blow a kiss orbicularis oris.

If there is weakness especially in a bilateral upper motor neuron distribution, get the patient to smile by telling a joke or funny story.

With a pseudobulbar palsy automatic or emotional facial expression will be more complete than movements to command. The examiner can use a cotton tip applicator dipped in a solution that is sweet, salty, sour, or bitter. Apply to one side then the other side of the extended tongue and have the patient decide on the taste before they pull their tongue back in to tell you their answer.

This can be done by the examiner lightly rubbing their fingers by each ear or by using a ticking watch. Compare right versus left. Further screening for conduction versus neurosensory hearing loss can be accomplished by using the Weber and Rinne tests. The Weber test consists of placing a vibrating tuning fork on the middle of the head and asking if the patient feels or hears it best on one side or the other.

The normal patient will say it is the same in both ears. The patient with unilateral neurosensory hearing loss will hear it best in the normal ear while the patient with a unilateral conductive hearing loss will hear it best in the abnormal ear. The Rinne test consists of comparing bone conduction placing the tuning fork on the mastoid process versus air conduction placing the tuning fork in front of the pinna.

Normally, air conduction is greater than bone conduction. For neurosensory hearing loss air conduction is still greater than bone conduction but for conduction hearing loss bone conduction will be greater than air conduction. Cranial Nerve 8 - Vestibular The vestibular division of CN 8 can be tested for by using the vestibulo-ocular reflex as already demonstrated or by using ice water calorics to test vestibular function.

The later test is usually reserved for patients who have vertigo or balance problems or in the comatose patient when one is testing brainstem function. The palate should rise symmetrically and there should be little nasal air escape. With unilateral weakness the uvula will deviate toward the normal side because that side of the palate is pulled up higher. With bilateral weakness neither side of the palate will elevate and there will be marked nasal air escape. This involuntary reflex is obtained by touching the back of the pharynx with the tongue depressor and watching the elevation of the palate.

Cranial Nerve 11 - Motor CN 11 is tested by asking the patient to shrug their shoulders trapezius muscles and turn their head sternocleidomastoid muscles against resistance. Cranial Nerve 12 - Motor The 12th CN is tested by having the patient stick out their tongue and move it side to side. Further strength testing can be done by having the patient push the tongue against a tongue blade.

With the red hatpin positioned equidistant between you and the patient, slowly move it laterally until the patient reports the disappearance of the top of the hatpin. The blind spot is normally found just temporal to central vision at eye level. The disappearance of the hatpin should occur at a similar point for you and the patient.

After the hatpin has disappeared for the patient, continue to move it laterally and ask the patient to let you know when they can see it again. The point at which the patient reports the hatpin re-appearing should be similar to the point at which it re-appears for you presuming the patient and you have a normal blind spot. You can further assess the superior and inferior borders of the blind spot using the same process. In the context of a cranial nerve examination, fundoscopy is performed to assess the optic disc for signs of pathology e.

You should offer to perform fundoscopy in your OSCE, however, it may not be required. See our dedicated fundoscopy guide for more details. The oculomotor nerve also carries parasympathetic fibres responsible for pupillary constriction. Briefly assess for abnormalities of eye movements which may be caused by underlying cranial nerve palsy e. Look at the eyes in the primary position for any deviation or abnormal movements.

Ask the patient to keep their head still whilst following your finger with their eyes. Ask them to let you know if they experience any double vision or pain.

Observe for any restriction of eye movement and note any nystagmus which may suggest vestibular nerve pathology or stroke. Damage to any of the three cranial nerves innervating the extraocular muscles can result in paralysis of the corresponding muscles.

Oculomotor palsy a. Oculomotor nerve palsy can also cause ptosis due to a loss of innervation to levator palpebrae superioris as well as mydriasis due to the loss of parasympathetic fibres responsible for innervating to the sphincter pupillae muscle. The only muscle the trochlear nerve innervates is the superior oblique muscle.

Patients often try to compensate for this by tilting their head forwards and tucking their chin in, which minimises vertical diplopia.

Trochlear nerve palsy also causes torsional diplopia as the superior oblique muscle assists with intorsion of the eye as the head tilts. To compensate for this, patients with trochlear nerve palsy tilt their head to the opposite side, in order to fuse the two images together. The abducens nerve CN VI innervates the lateral rectus muscle. Patients typically present with horizontal diplopia which is worsened when they attempt to look towards the affected side.

Strabismus is a condition in which the eyes do not properly align with each other when looking at an object. Pathology affecting the oculomotor, trochlear or abducens nerves can cause strabismus. Ask the patient to focus on a target approximately half a metre away whilst you shine a pen torch towards both eyes.

The direction of the shift in fixation determines the type of tropia; the table below describes the appropriate interpretation. The trigeminal nerve CN V transmits both sensory information about facial sensation and motor information to the muscles of mastication. The trigeminal nerve has three sub-divisions , each of which has its own broad set of functions not all are covered below :. First, explain the modalities of sensation you are going to assess e.

This provides them with a reference of what the sensation should feel like assuming they have no sensory deficits in the region overlying the sternum. Assess the sensory component of V 1 , V 2 and V 3 by testing light touch and pinprick sensation across regions of the face supplied by each branch:. You should compare each region on both sides of the face to allow the patient to identify subtle differences in sensation.

Use the muscles of mastication to assess the motor component of V 3 :. Inspect the temporalis located in the temple region and masseter muscles located at the posterior jaw for evidence of wasting. This is typically most noticeable in the temporalis muscles, where a hollowing effect in the temple region is observed. Palpate the masseter muscle located at the posterior jaw bilaterally whilst asking the patient to clench their teeth to allow you to assess and compare muscle bulk.

Ask the patient to open their mouth whilst you apply resistance underneath the jaw to assess the lateral pterygoid muscles.

An inability to open the jaw against resistance or deviation of the jaw typically to the side of the lesion may occur in trigeminal nerve palsy. The jaw jerk reflex is a stretch reflex that involves the slight jerking of the jaw upwards in response to a downward tap. This response is exaggerated in patients with an upper motor neuron lesion. Both afferent and efferent pathways of the jaw jerk reflex involve the trigeminal nerve.

Clearly explain what the procedure will involve to the patient and gain consent to proceed. In healthy individuals, this should trigger a slight closure of the mouth. In patients with upper motor neuron lesions, the jaw may briskly move upwards causing the mouth to close completely. The corneal reflex involves involuntary blinking of both eyelids in response to unilateral corneal stimulation direct and consensual blinking.

The afferent branch of the corneal reflex involves V1 of the trigeminal nerve whereas the efferent branch is mediated by the temporal and zygomatic branches of the facial nerve. In healthy individuals, you should observe both direct and consensual blinking.

The absence of a blinking response suggests pathology involving either the trigeminal or facial nerve. The corneal reflex is not usually assessed in an OSCE scenario, however, you should offer to test it and understand the purpose behind the test.

The facial nerve CN VII transmits motor information to the muscles of facial expression and the stapedius muscle involved in the regulation of hearing. The facial nerve also has a sensory component responsible for the conveyance of taste from the anterior two-thirds of the tongue. Ask the patient if they have noticed any recent changes in their sense of taste. Ask the patient if they have noticed any changes to their hearing paralysis of the stapedius muscle can result in hyperacusis.

Ask the patient to carry out a sequence of facial expressions whilst again observing for asymmetry :. Facial nerve palsy presents with unilateral weakness of the muscles of facial expression and can be caused by both upper and lower motor neuron lesions.

Facial nerve palsy caused by a lower motor neuron lesion presents with weakness of all ipsilateral muscles of facial expression, due to the loss of innervation to all muscles on the affected side.

The most common cause of upper motor neuron facial palsy is stroke. The vestibulocochlear nerve CN VIII transmits sensory information about sound and balance from the inner ear to the brain. The vestibulocochlear nerve has no motor component. Position yourself approximately 60cm from the ear and then whisper a number or word.

Mask the ear not being tested by rubbing the tragus. Do not place your arm across the face of the patient when rubbing the tragus, it is far nicer to occlude the ear from behind the head.

Ask the patient to repeat the number or word back to you. If they get two-thirds or more correct then their hearing level is 12db or better. If there is no response use a conversational voice 48db or worse or loud voice 76db or worse. If there is no response you can move closer and repeat the test at 15cm. Here the thresholds are 34db for a whisper and 56db for a conversational voice.

Place a vibrating Hz tuning fork firmly on the mastoid process apply pressure to the opposite side of the head to make sure the contact is firm. This tests bone conduction.

Confirm the patient can hear the sound of the tuning fork and then ask them to tell you when they can no longer hear it. When the patient can no longer hear the sound, move the tuning fork in front of the external auditory meatus to test air conduction.

Ask the patient if they can now hear the sound again. Tap a Hz tuning fork and place in the midline of the forehead. A Hz tuning fork is used as it gives the best balance between time of decay and tactile vibration. Ideally, you want a tuning fork that has a long period of decay and cannot be detected by vibration sensation.

Tap a Hz tuning fork and place in the midline of the forehead Conductive vs sensorineural hearing loss Conductive hearing loss occurs when sound is unable to effectively transfer at any point between the outer ear, external auditory canal, tympanic membrane and middle ear ossicles.

Causes of conductive hearing loss include excessive ear wax, otitis externa, otitis media, perforated tympanic membrane and otosclerosis. Causes of sensorineural hearing loss include increasing age presbycusis , excessive noise exposure, genetic mutations, viral infections e. Ask the patient to march on the spot with their arms outstretched and their eyes closed:. Before performing this test you need to check if the patient has any neck problems and if so you should not proceed.

Explain to the patient that the test will involve briskly turning their head and then gain consent to proceed. Sit facing the patient and ask them to fixate on your nose at all times during the test. Hold their head in your hands one hand covering each ear and rotate it rapidly to the left, at a medium amplitude.

The normal response is that ocular fixation is maintained. In a patient with loss of vestibular function on one side, the eyes will first move in the direction of the head losing fixation , before a corrective refixation saccade occurs towards your nose.

The glossopharyngeal nerve transmits motor information to the stylopharyngeus muscle which elevates the pharynx during swallowing and speech. The glossopharyngeal nerve also transmits sensory information that conveys taste from the posterior third of the tongue. Visceral sensory fibres of CN IX also mediate the afferent limb of the gag reflex. The vagus nerve transmits motor information to several muscles of the mouth which are involved in the production of speech and the efferent limb of the gag reflex.