Neurological Physical Examination Basics

The neurological physical exam is your foundational clinical detective tool. It allows you to localize a lesion within the nervous system—distinguishing between central and peripheral causes, identifying specific cranial nerves, or pinpointing spinal cord levels—long before imaging is ordered. Mastering this systematic approach transforms vague symptoms into a precise anatomical roadmap, guiding all subsequent diagnosis and management. For any pre-med or medical student, proficiency here is non-negotiable.

The Systematic Cranial Nerve Examination

A methodical approach from CN I to CN XII prevents crucial omissions. Think of it as a head-to-neck circuit check.

CN I (Olfactory): Test each nostril separately with a familiar, non-irritating substance like coffee or soap. Anosmia (loss of smell) can result from trauma, frontal lobe tumors, or neurodegenerative diseases like Parkinson's. Importantly, nasal congestion must be ruled out as a cause.

CN II (Optic): Assess visual acuity, visual fields by confrontation, and funduscopic examination. The afferent pupillary defect (Marcus Gunn pupil) is a critical finding: when a light is swung from the normal eye to the affected eye, both pupils dilate because the damaged optic nerve perceives less light.

CN III, IV, VI (Oculomotor, Trochlear, Abducens): These nerves control eye movements. Test the six cardinal positions of gaze. A CN III palsy causes ptosis, a "down and out" eye position, and pupillary dilation. Isolated CN IV palsy leads to difficulty looking down when the eye is turned inward (e.g., going down stairs). CN VI palsy results in an inability to abduct the eye.

CN V (Trigeminal): This nerve has both motor and sensory functions. Test light touch and pain sensation on the three divisions of the face (ophthalmic V1, maxillary V2, mandibular V3). Motor function is assessed by palpating the masseter and temporalis muscles while the patient clenches their jaw.

CN VII (Facial): Observe for asymmetry at rest and during movement. Test motor function by having the patient raise eyebrows, close eyes tightly, puff cheeks, and show teeth. A central lesion (e.g., stroke) typically spares the forehead due to bilateral innervation, while a peripheral lesion (e.g., Bell's palsy) affects the entire ipsilateral side.

CN VIII (Vestibulocochlear): Test hearing via finger rub or whisper. Assess balance, which integrates with cerebellar function. The Weber and Rinne tests use a tuning fork to differentiate conductive from sensorineural hearing loss.

CN IX & X (Glossopharyngeal & Vagus): These are tested together. Observe the palate's position at rest; it should be symmetrical. Have the patient say "ah" – the uvula should elevate midline. A unilateral lesion causes the uvula to deviate away from the side of the lesion. The gag reflex tests both sensory (CN IX) and motor (CN X) components.

CN XI (Spinal Accessory): Test the sternocleidomastoid by having the patient turn their head against resistance. Test the trapezius by having them shrug shoulders against resistance.

CN XII (Hypoglossal): Inspect the tongue for atrophy or fasciculations at rest. Have the patient protrude the tongue; it will deviate toward the side of a unilateral lesion.

Motor, Reflex, and Sensory System Assessment

This segment evaluates the pathways from the cortex down the spinal cord to the peripheral nerve and muscle.

Motor Strength Grading: Strength is graded on a standard five-point scale. This objective measure is crucial for tracking progression:

• 5/5: Full strength against resistance.
• 4/5: Movement against some resistance but less than full.
• 3/5: Can overcome gravity but not resistance (e.g., lifting arm off bed).
• 2/5: Can move only with gravity eliminated (e.g., sliding arm across bed).
• 1/5: Flicker or trace of contraction.
• 0/5: No muscle contraction.

Deep Tendon Reflexes (DTRs): These assess the integrity of the sensory neuron, spinal cord synapse, and motor neuron (the reflex arc). Grade them from 0 to 4+. Asymmetry is often more telling than absolute value. Key reflexes are biceps (C5, C6), triceps (C7), brachioradialis (C6), patellar (L4), and Achilles (S1).

The Babinski Sign: This is a critical test of upper motor neuron integrity. Using a blunt object, stroke the lateral sole of the foot from heel to ball, then curve medially. The normal response in adults is plantar flexion of the toes. An abnormal response, the Babinski sign, is characterized by dorsiflexion of the great toe and fanning of the others. It indicates a lesion in the corticospinal tract.

Sensory Modality Testing: Different pathways carry different sensations. Test key modalities systematically:

• Light Touch: Use a wisp of cotton.
• Pain and Temperature: Use a sterile pin and a cool tuning fork. These travel together in the spinothalamic tract.
• Vibration and Proprioception: Test with a 128-Hz tuning fork on bony prominences and by moving a patient's digit up/down. These travel in the dorsal columns.
• Map out any deficits in a "stocking-glove" pattern (suggestive of peripheral neuropathy) or a dermatomal pattern (suggestive of nerve root injury).

Coordination, Balance, and Gait

These functions integrate sensory input, cerebellar processing, and motor output. Abnormalities here are often glaring and highly localizing.

Cerebellar Function Tests:

• Finger-to-Nose Test: With the patient's eyes open, have them repeatedly touch their nose, then your finger, which you move. Look for intention tremor (worsening tremor as finger approaches target) and dysmetria (consistent overshoot or undershoot).
• Heel-to-Shin Test: With the patient supine, have them place one heel on the opposite knee and slide it smoothly down the shin to the ankle. Cerebellar disease causes a shaky, irregular motion.
• Rapid Alternating Movements: Have the patient pat their knee, alternating palm and back of hand, or tap their foot. Dysdiadochokinesia is a slow, clumsy, irregular rhythm.

The Romberg Test: This is a test of proprioception (sensory ataxia), not cerebellar function. Ask the patient to stand with feet together and eyes open, then close their eyes. Stand close to catch them. A patient with impaired proprioception will be stable with eyes open but sway or fall with eyes closed (a positive Romberg sign). A patient with cerebellar ataxia will sway regardless of vision.

Gait Observation: Simply watching a patient walk is profoundly informative. Note:

• Hemiparetic gait: Circumduction of a weak leg.
• Steppage gait: Excessive lifting of the knee (foot drop).
• Ataxic gait: Wide-based, unsteady, staggering.
• Parkinsonian gait: Shuffling, festinating (small, accelerating steps), decreased arm swing.

Common Pitfalls

1. Skipping the Funduscopic Exam: Failing to look at the optic disc can mean missing papilledema (a sign of elevated intracranial pressure) or other critical findings like retinal hemorrhages. It's a challenging skill but an essential one.
2. Misinterpreting Reflex Findings: Isolating a reflex grade without context is useless. Always compare side-to-side. Hyperreflexia (4+) suggests an upper motor neuron lesion, while absent reflexes (0) suggest a lower motor neuron or profound muscle disease. Remember that hyporeflexia can be normal in some elderly patients.
3. Incorrect Babinski Technique: Stroking too medially or too lightly can elicit a withdrawal response (a false negative). The stimulus must be firm enough and follow the proper lateral-to-medial path across the ball of the foot.
4. Overlooking Gait: Saving gait observation for last or skipping it if the patient is in bed is a major error. Gait integrates almost every part of the neurological exam. Always make a point to watch the patient walk, even a few steps.

Summary

• The neurological exam is a systematic, hypothesis-driven tool for localizing pathology within the nervous system, starting with a meticulous cranial nerve examination from I to XII.
• Motor strength is objectively graded on a 0-5 scale, deep tendon reflexes are assessed for symmetry, and the Babinski sign is a key indicator of upper motor neuron dysfunction.
• Sensory testing must evaluate distinct pathways (spinothalamic for pain/temperature, dorsal columns for vibration/proprioception) to localize lesions in the spinal cord or periphery.
• Cerebellar function is tested via coordination tasks like finger-to-nose and heel-to-shin, while the Romberg test specifically assesses proprioceptive (sensory) ataxia.
• Gait observation is a non-invasive yet high-yield component that provides an integrated view of motor, sensory, and cerebellar function.