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CNS Examination in Detail

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Overview and Approach

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I. MENTAL STATUS EXAMINATION

A. Level of Consciousness and Attention

• Alert - fully awake and responsive
• Drowsy/Somnolent - arousable by verbal stimuli
• Stupor - arousable only by vigorous/painful stimuli
• Coma - unarousable

• Digit Span Test - Forward: read digits at 1/sec, patient repeats; Normal = 7 ± 2 digits. Backward: Normal = 5 ± 1
• Serial Subtraction - Subtract 7s from 100 (100, 93, 86...) or 3s; tests concentration
• "A" Vigilance Test - Tap each time letter "A" is heard in a random letter sequence
• Palm-Side-Fist sequence - Three-step motor sequence (frontal lobe function)

B. Orientation

• Time: Date, day, month, year, time of day (off by >3 days on date or >4 hours on time = significantly disoriented)
• Place: Hospital/clinic, type of place, city
• Person: Own name (rarely lost except in severe dementia)

C. Memory

D. Language

E. Praxis (Motor Planning)

• Commanded and imitated gestures: hammering a nail, blowing out a candle, throwing dice
• Sequential hand positions (Luria three-step: fist-edge-palm)
• Dressing apraxia: observed while patient dresses

F. Visuospatial Function / Gnosis

• Clock drawing test: Draw clock face, place numbers, set time to 10 past 11
• Line bisection: Bisect a horizontal line (neglect = bisects off-center)
• Copy figures: Pentagon intersection, cube
• Floor plan drawing: Sketch layout of own home
• Object recognition (Gnosis): Name objects by sight, by touch (stereognosis), by sound

G. Executive Function and Judgment

• Abstract reasoning: Interpret proverbs ("A rolling stone gathers no moss")
• Similarities: "In what way are an apple and an orange alike?"
• Judgment: "What would you do if you found a stamped, addressed envelope on the street?"
• Insight into own illness: Does patient recognize their deficit?

H. Frontal Lobe Specific Tests

• Go/No-Go task: Tap when examiner taps once; do not tap when examiner taps twice
• Perseveration: Alternate sequence drawing (square-triangle-square-triangle); Luria loops
• Grasp reflex, Palmomental reflex, Gegenhalten (paratonia)

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II. CRANIAL NERVE EXAMINATION

CN I - Olfactory Nerve

• Indicated in: head trauma, suspected Parkinson's disease, anterior cranial fossa lesions, meningioma.

CN II - Optic Nerve

1. Visual Acuity - Snellen chart at 6 metres (20 feet) for each eye separately; pinhole corrects refractive error; near card (Rosenbaum) for bedside
2. Visual Fields - Confrontation testing (each eye tested separately, examiner's face as central fixation point); count fingers or wiggling fingers in four quadrants; for detailed mapping - perimetry/Goldman fields
3. Color vision - Ishihara plates (sensitive for optic nerve disease)
4. Fundoscopy - Optic disc (pallor, papilloedema, cupping), vessels, macula

CN III, IV, VI - Oculomotor, Trochlear, Abducens

1. Pupillary examination:
   • Size (normal 2-5 mm), shape, symmetry
   • Direct and consensual light reflex (afferent = CN II, efferent = CN III)
   • Swinging flashlight test - RAPD (relative afferent pupillary defect) = optic nerve or severe retinal disease
   • Near reflex (accommodation-convergence)
   • Anisocoria: >1 mm difference - test in light and dark (Horner vs CN III)
2. Eye movements:
   • Saccades: rapid voluntary movements ("Look left/right quickly")
   • Smooth pursuit: follow slowly moving finger (H-pattern)
   • Vergence: convergence
   • Vestibulo-ocular reflex (VOR): doll's head maneuver
   • Nystagmus: direction, type (horizontal/vertical/torsional), fast vs slow phase
3. Ptosis: CN III (complete, with pupil dilation) vs Horner's (partial, with miosis, anhidrosis)

CN V - Trigeminal Nerve

1. Sensation - Test pinprick and light touch in all three divisions (V1 ophthalmic, V2 maxillary, V3 mandibular) bilaterally; also test cornea
2. Corneal reflex - Touch cornea gently with wisp of cotton; normal = bilateral blink (afferent CN V1, efferent CN VII); come from side to avoid visual stimulus
3. Motor division - Jaw strength: clench teeth (masseter/temporalis bulk), open jaw against resistance (pterygoids); jaw deviates to weak side on opening
4. Jaw jerk - Tap chin with finger; brisk = upper motor neuron lesion above pons

CN VII - Facial Nerve

1. Observe at rest, during speech and spontaneous smiling (subtle weakness more evident)
2. Upper face: Raise eyebrows (frontalis), tightly close eyes (resist opening - orbicularis oculi)
3. Lower face: Puff cheeks, whistle, show teeth (smile to command), purse lips
4. Upper vs Lower motor neuron distinction: UMN (central) lesion spares forehead due to bilateral cortical innervation; LMN (Bell's palsy) involves entire ipsilateral hemiface
5. Taste: Anterior 2/3 tongue (chorda tympani, branches of CN VII) - sweet, salt, sour on tongue tip
6. Hyperacusis: Loud sounds perceived more intensely (stapedius muscle paralysis - LMN CN VII)

CN VIII - Vestibulocochlear

1. Whispered voice test: Whisper 2-syllable words at 60 cm behind each ear separately
2. Rinne test: 512 Hz tuning fork - compare air conduction (ear canal) vs bone conduction (mastoid); Normal/SNHL: AC > BC (Rinne positive); Conductive loss: BC > AC (Rinne negative)
3. Weber test: Vibrating fork on center of forehead; lateralizes to better ear in SNHL; lateralizes to worse ear in conductive loss
4. Formal audiometry if abnormality detected

1. Romberg test: Feet together, arms at sides; maintain balance eyes open then eyes closed (positive = falls with eyes closed = proprioceptive or vestibular loss)
2. Marching test (Unterberger): March on spot with eyes closed; rotates to side of vestibular lesion
3. Dix-Hallpike test: For BPPV
4. Head impulse test: Rapid horizontal head thrust; corrective saccade = vestibular hypofunction

CN IX & X - Glossopharyngeal and Vagus

1. Phonation: Ask "aah" - observe soft palate elevation; deviates to normal side if unilateral weakness; bilateral weakness = nasal voice, regurgitation
2. Gag reflex: Touch posterior pharyngeal wall or tonsillar pillar - afferent IX, efferent X; reduced in lower motor neuron lesions
3. Swallowing: Observe for coughing, nasal regurgitation; CN X lesion causes dysphagia
4. Voice quality: Hoarseness or bovine cough = recurrent laryngeal nerve (CN X) lesion

CN XI - Accessory Nerve

1. Sternocleidomastoid: Turn head against resistance (turns head to contralateral side); test each separately
2. Trapezius: Shoulder shrug against resistance; ipsilateral weakness

CN XII - Hypoglossal Nerve

1. Tongue at rest: Observe for fasciculations, atrophy (LMN lesion)
2. Tongue protrusion: Deviates to side of weakness (LMN) or away from lesion (UMN)
3. Rapid tongue movements: "La-la-la" (lingual sounds)
4. Dysarthria: "Linguo-labial" sounds affected

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III. MOTOR SYSTEM EXAMINATION

A. Inspection

• Muscle bulk: Wasting/atrophy (LMN, disuse, myopathy), hypertrophy (muscular dystrophy, hypothyroid myopathy)
• Fasciculations: Spontaneous visible muscle twitching at rest (LMN / anterior horn cell disease)
• Abnormal movements: Tremor (rest vs action), chorea, athetosis, ballismus, dystonia, myoclonus, tics
• Posture at rest: External rotation of hip (UMN lesion), hemiplegic posture

B. Tone

• Normal: Mild resistance to passive movement
• Hypotonia: Reduced resistance (cerebellar, LMN, acute spinal shock, chorea)
• Spasticity: Velocity-dependent increased resistance (pyramidal/UMN lesion); "clasp-knife" - give-way at end; greater in arm flexors and leg extensors
• Rigidity: Uniform increased resistance throughout range (extrapyramidal); "lead-pipe" or "cogwheel" (Parkinson's - Froment's sign: cogwheeling enhanced by contralateral arm movement)
• Gegenhalten (Paratonia): Variable resistance, mirrors examiner's pressure (frontal lobe lesion)
• Clonus: Rhythmic oscillating contractions at sustained stretch (brisk at ankle); >5 beats = pathological

C. Power (Strength)

• Shoulder abduction (C5, deltoid), adduction (C6-8, pectoral/lat)
• Elbow flexion (C5-6, biceps), extension (C7, triceps)
• Wrist extension (C6-7, extensors), flexion (C6-7, flexors)
• Finger extension (C7, extensor digitorum), flexion (C8, FDP/FDS)
• Finger abduction/adduction (T1, interossei)
• Thumb opposition (C8-T1, abductor pollicis brevis)

• Hip flexion (L1-2, iliopsoas), extension (L5-S1, gluteus maximus)
• Hip abduction (L4-5, gluteus medius), adduction (L2-4, adductors)
• Knee extension (L3-4, quadriceps), flexion (L5-S1, hamstrings)
• Ankle dorsiflexion (L4-5, tibialis anterior), plantarflexion (S1-2, gastrocnemius)
• Hallux extension (L5, EHL), toe flexion (S1-2)

• Pronator drift: Arms outstretched, palms up, eyes closed for 10 seconds; pronation and downward drift = UMN lesion; upward drift = sensory ataxia; arm "orbiting" away = subtle weakness
• Barre's sign (legs): Patient prone, knees bent at 90°; affected leg drifts down
• Heel-walking, toe-walking: Foot drop (L4-5) vs S1 weakness; "rise on toes" - assess with patient standing at wall

D. Coordination (Cerebellar Function)

• Finger-nose-finger test: Patient touches own nose then examiner's finger back and forth; look for intention tremor, dysmetria, past-pointing
• Rapid alternating movements (Dysdiadochokinesia): Alternating pronation/supination ("patting the back of hand"), or rapidly touching each fingertip with thumb
• Rebound test: Suddenly release flexed arm against examiner's resistance; cerebellar disease = delayed check/overshoot

• Heel-shin test: Heel placed on opposite knee, run smoothly down shin to ankle; cerebellar disease = ataxic, irregular path
• Foot tapping: Tap foot rapidly on examiner's hand
• Toe-finger test

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IV. REFLEXES

A. Deep Tendon Reflexes (Muscle Stretch Reflexes)

• 0 = Absent
• 1+ = Present only with reinforcement (Jendrassik maneuver - clasp hands and pull)
• 2+ = Normal
• 3+ = Brisk (may be normal)
• 4+ = Very brisk with clonus (pathological - UMN)

B. Plantar Response (Babinski Sign)

• Stroke the lateral aspect of sole from heel toward ball and across to big toe
• Normal (flexor response): Plantar flexion of toes
• Abnormal (Babinski sign, extensor response): Dorsiflexion of big toe ± fanning of other toes = damage to corticospinal tract (UMN)
• Withdrawal response: Quick withdrawal of whole foot (not Babinski)
• Triple flexion response: Flexion of hip, knee, dorsiflexion of foot (pathological, similar significance to Babinski)

• Oppenheim: Knuckle pressed firmly down the shin
• Gordon: Squeezing the calf
• Chaddock: Lateral aspect of dorsum of foot from lateral malleolus forward
• Bing: Prick dorsum of foot with pin

C. Superficial Reflexes

• Abdominal reflexes: Stroke skin from lateral to midline in each quadrant; reflex absent ipsilateral to pyramidal lesion; absent bilaterally in obese patients (less reliable)
• Cremasteric reflex: Stroke inner thigh; cremasteric muscle contracts, scrotal sac rises; Lost in UMN lesions, ipsilateral cord/root lesion
• Anal reflex: Perianal skin scratch; anal sphincter contracts; Loss = S3-S5 lower motor neuron
• Bulbocavernosus reflex: Squeeze glans penis/tap pubic symphysis; contraction of bulbocavernosus; Loss = sacral cord/conus lesion

D. Primitive (Pathological) Reflexes

• Grasp reflex: Stimulate palm; involuntary grasping (frontal lobe lesion)
• Palmomental reflex: Scratch thenar eminence; ipsilateral chin muscle contracts (frontal lobe)
• Snout reflex: Tap philtrum; pursing of lips (bilateral frontal disease)
• Glabellar tap: Repeated taps on glabella; normal = habituates after 2-3 taps; Parkinson's = does not habituate (Myerson's sign)
• Rooting and sucking reflexes: Normally present in infants; return in severe dementia/frontal lobe disease

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V. SENSORY EXAMINATION

A. Primary (Modality-Specific) Sensations

B. Cortical Sensory Modalities

• Stereognosis: Identify common objects (key, coin, pen) placed in hand without looking
• Graphesthesia: Identify numbers or letters written on palm
• Two-point discrimination: Minimum distance for perceiving two distinct touch stimuli; fingertip normal = 2-5 mm; loss = parietal lesion
• Sensory extinction (double simultaneous stimulation): Touch both sides simultaneously; patient reports only one side (extinction/neglect = parietal lobe, usually non-dominant)
• Point localization: Patient points to where examiner touches with eyes closed

C. Patterns of Sensory Loss

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VI. GAIT AND STATION

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VII. SCREENING NEUROLOGICAL EXAMINATION (Quick Reference)

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VIII. SPECIAL EXAMINATION CONSIDERATIONS

Meningeal Signs

• Neck stiffness (Nuchal rigidity): Passive neck flexion resisted; chin-to-chest test; indicates meningeal irritation (meningitis, subarachnoid hemorrhage)
• Kernig's sign: Flex hip to 90° then extend knee - resistance/pain at <135° = positive
• Brudzinski's sign: Passive neck flexion causes involuntary hip and knee flexion
• Jolt accentuation: Horizontal head rotation at 2-3 Hz worsens headache = meningitis

Signs of Raised Intracranial Pressure

• Papilloedema on fundoscopy
• Sixth nerve palsy (false localizing sign)
• Cushing's triad: bradycardia, hypertension, irregular respiration

Upper vs Lower Motor Neuron Differentiation

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Sources

• Adams and Victor's Principles of Neurology, 12th Edition - Chapter 1 (Approach to the Patient with Neurologic Disease), pp. 18-21
• Bradley and Daroff's Neurology in Clinical Practice - Chapter 1 (Neurological Examination), Table 1.1
• Harrison's Principles of Internal Medicine, 22nd Edition - Mental Status Examination section

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What's inside (12 pages)