What is the appropriate CNS examination and management for a patient with left 6th (sixth) cranial nerve palsy, left Lower Motor Neuron (LMN) facial palsy, right hemiparesis, and left horizontal gaze palsy?

CNS Examination Format for Left Pontine Syndrome

This constellation of findings—left 6th nerve palsy, left LMN facial palsy, right hemiparesis, and left horizontal gaze palsy—localizes to a left pontine lesion, most likely affecting the left facial colliculus and adjacent corticospinal tract, requiring urgent neuroimaging to identify the underlying cause (typically stroke, tumor, or demyelinating disease). 1

Anatomical Localization

The combination of these specific deficits points directly to the pons:

• Left 6th nerve nucleus involvement produces both the left 6th nerve palsy AND the left horizontal gaze palsy, since the abducens nucleus contains not only motor neurons for the lateral rectus but also interneurons that coordinate conjugate horizontal gaze 1
• Left 7th nerve fascicle involvement (as it curves around the 6th nerve nucleus in the facial colliculus) causes the ipsilateral LMN facial palsy 1, 2
• Left corticospinal tract involvement (as the 6th nerve courses through these tracts within the pons) produces the contralateral (right) hemiparesis 1

Systematic CNS Examination Components

Mental Status and Higher Cortical Function

• Level of consciousness: Alert, oriented to person/place/time, or any alteration 1
• Speech and language: Assess for dysarthria (pontine lesions can affect speech articulation) or aphasia (suggests additional cortical involvement) 1
• Cognitive screening: Attention, memory, executive function if clinically indicated 1

Cranial Nerve Examination (Detailed Focus)

CN II (Optic Nerve):

• Visual acuity: Best-corrected acuity in each eye to screen for optic nerve involvement 1, 3
• Pupillary examination: Check for afferent pupillary defect, pupil size and reactivity 1, 3
• Fundoscopy: Look specifically for papilledema (suggests increased intracranial pressure) or optic atrophy 1, 3, 4
• Visual fields: Confrontation testing to exclude additional pathology 1

CN III, IV (Oculomotor, Trochlear):

• Pupil involvement: Document if pupils are equal and reactive (pupil-sparing vs pupil-involving helps localize) 5
• Vertical eye movements: Assess elevation, depression to ensure no additional cranial nerve involvement 1, 5
• Eyelid position: Check for ptosis (would suggest 3rd nerve involvement) 1

CN V (Trigeminal):

• Facial sensation: Test all three divisions (V1, V2, V3) bilaterally, as cavernous sinus lesions can affect CN V1 with CN VI 1
• Corneal reflex: Afferent limb (CN V) and efferent limb (CN VII) 1
• Jaw strength: Masseter and temporalis muscle strength 1

CN VI (Abducens) - PRIMARY FINDING:

• Horizontal eye movements: Document complete inability to abduct the left eye past midline 1
• Incomitant esotropia: Measure deviation in primary position, worse at distance than near, and increased when looking toward the affected (left) side 1, 3
• Compensatory head turn: Document if patient turns head to the left to minimize diplopia 1, 3
• Forced duction testing: Distinguish mechanical restriction from true paresis 5
• Forced generation testing: Assess residual lateral rectus function 1

CN VII (Facial) - PRIMARY FINDING:

• Upper face: Inability to wrinkle forehead or close eye on LEFT side (LMN pattern affects both upper and lower face) 2
• Lower face: Inability to smile, show teeth, puff cheeks on LEFT side 2
• Distinguish LMN from UMN: In LMN palsy, forehead is affected; in UMN palsy, forehead is spared 2
• Taste: Anterior 2/3 of tongue if chorda tympani involved 2

CN VIII (Vestibulocochlear):

• Hearing: Assess for asymmetric hearing loss (pontine lesions can affect nearby CN VIII) 2
• Vestibular function: Nystagmus, Dix-Hallpike if vertigo present 2

CN IX, X, XI, XII:

• Palate elevation: Symmetric rise with "ah" 1
• Gag reflex: Present and symmetric 1
• Tongue protrusion: Midline without deviation 1
• Shoulder shrug and head turn: Sternocleidomastoid and trapezius strength 1

Eye Movement Examination (Critical Component)

Horizontal Gaze Palsy Assessment:

• Voluntary gaze: Document inability to move BOTH eyes to the left (left horizontal gaze palsy) 1
• Vestibulo-ocular reflex (Doll's eyes): Turn head rapidly to right and left—in true gaze palsy, eyes CANNOT cross midline even with this maneuver, confirming nuclear/infranuclear lesion rather than supranuclear gaze preference 5
• Optokinetic nystagmus: Absent or reduced when targets move toward the affected side 5
• Saccades: Assess speed and accuracy in all directions 5
• Smooth pursuit: Test in horizontal and vertical planes 5
• Convergence: Near point of convergence 5

Diplopia Characterization:

• Horizontal diplopia: Worse at distance, worse looking toward affected (left) side 1, 3
• Binocular vs monocular: Resolves with either eye covered (binocular) 1, 3

Motor Examination (Right Hemiparesis)

Upper Extremity:

• Tone: Assess for spasticity, rigidity, or flaccidity in right arm 1
• Strength: Test shoulder abduction, elbow flexion/extension, wrist extension, finger abduction, grip strength—grade 0-5/5 on right side 1
• Pronator drift: Right arm drifts downward and pronates 1

Lower Extremity:

• Tone: Assess right leg 1
• Strength: Hip flexion, knee extension/flexion, ankle dorsiflexion/plantarflexion—grade 0-5/5 on right side 1

Pattern Recognition:

• Pyramidal pattern: Typically greater weakness in extensors of upper extremity and flexors of lower extremity 1

Sensory Examination

Primary Modalities:

• Light touch: Compare right vs left, all four extremities 1
• Pinprick: Right vs left comparison 1
• Temperature: If indicated 1
• Proprioception: Toe and finger position sense, particularly on right side 1
• Vibration: Tuning fork at toes and fingers bilaterally 1

Cortical Sensory Function:

• Two-point discrimination: If cortical involvement suspected 1
• Graphesthesia: Number writing on palm 1
• Stereognosis: Object identification 1

Cerebellar Examination

Coordination:

• Finger-to-nose: Assess for dysmetria, intention tremor bilaterally 2
• Heel-to-shin: Test both legs 2
• Rapid alternating movements: Hand patting, finger tapping 2

Gait and Station:

• Stance: Narrow-based vs broad-based, truncal ataxia 2
• Tandem gait: Walk heel-to-toe 2
• Romberg test: Eyes open then closed 2

Reflexes

Deep Tendon Reflexes:

• Upper extremity: Biceps, triceps, brachioradialis—compare right vs left, expect hyperreflexia on right with corticospinal tract lesion 1
• Lower extremity: Patellar, Achilles—compare right vs left 1
• Grading: 0 (absent) to 4+ (hyperactive with clonus) 1

Pathological Reflexes:

• Babinski sign: Extensor plantar response on RIGHT side (upgoing toe) indicates corticospinal tract involvement 1
• Hoffman sign: Flick distal phalanx of middle finger, watch for thumb flexion on right 1
• Clonus: Sustained rhythmic contractions at ankle on right 1

Additional Critical Assessments

Vital Signs:

• Blood pressure: Hypertension is major risk factor for vasculopathic 6th nerve palsy and pontine stroke 1, 3
• Heart rate and rhythm: Atrial fibrillation increases stroke risk 1
• Temperature: Fever suggests infectious/inflammatory etiology 1

Meningeal Signs:

• Neck stiffness: With headache suggests meningitis or increased intracranial pressure 1, 4
• Kernig and Brudzinski signs: If meningeal irritation suspected 1, 4

Signs of Increased Intracranial Pressure:

• Headache pattern: New, severe, progressive 1, 4
• Papilledema on fundoscopy: Bilateral 6th nerve palsy can occur with increased ICP 1, 4
• Altered consciousness: Declining mental status 1, 4

Urgent Diagnostic Workup

Immediate Neuroimaging:

• MRI brain with and without contrast: Gold standard to identify pontine infarct, hemorrhage, tumor, or demyelinating plaque 1, 3, 4
• Include small field-of-view high-resolution T2-weighted images: Better visualization of brainstem structures 5
• CT head without contrast: If MRI unavailable or contraindicated, though less sensitive for posterior fossa 1, 4

Laboratory Testing:

• Serum glucose and hemoglobin A1c: Diabetes is common vasculopathic cause 1, 3, 4
• Lipid panel: Assess vascular risk 1
• Complete blood count: Rule out infection, anemia 6
• ESR and CRP: If giant cell arteritis suspected (though less likely with this localization) 1, 3

Additional Studies if Indicated:

• Lumbar puncture: ONLY after neuroimaging if concern for meningitis or increased ICP 1, 4
• MRA or CTA: If vascular abnormality suspected (vertebrobasilar insufficiency, aneurysm) 5, 6

Critical Clinical Pitfalls

Do not dismiss as isolated peripheral 7th nerve palsy: The presence of 6th nerve involvement, gaze palsy, and contralateral hemiparesis mandates central localization 2

Do not delay imaging in young patients: While vasculopathic causes are common in elderly with diabetes/hypertension, young patients require immediate imaging as neoplasm, demyelination, or other serious pathology is more likely 1, 3, 2

Recognize that LMN facial palsy can be central: The facial colliculus syndrome produces LMN facial weakness because the lesion affects the 7th nerve fascicle before it exits the brainstem 2

Distinguish gaze palsy from gaze preference: Use vestibulo-ocular reflex—in true gaze palsy (nuclear lesion), eyes cannot cross midline even with head turning; in gaze preference (cortical lesion), eyes can cross midline 5

Monitor for progression: If symptoms worsen or new deficits emerge, repeat neurological examination and consider repeat imaging 2

Check for bilateral 6th nerve involvement: Bilateral palsies suggest increased intracranial pressure, clival chordoma, or meningeal process requiring different management 1, 4