4.3 Standard Neurological Testing

Why Standard Neurological Testing Matters

The standard neurological screening examination localizes a lesion to a specific spinal nerve root, a peripheral nerve, the spinal cord, or a site above the cord, by combining motor (myotome), sensory (dermatome), and reflex (deep tendon reflex) findings into one coherent clinical picture. Part III vignettes consistently reward candidates who integrate all three data types to name a single level or lesion, rather than treating each finding as an isolated fact.

Myotomes: Testing Motor Nerve Roots

A myotome is the group of muscles primarily innervated by a single spinal nerve root. Because most muscles receive contributions from more than one root, myotome testing uses a resisted, isolated joint action that best isolates the dominant root for that muscle group, and strength is graded on the 0-5 Manual Muscle Testing (MRC) scale:

Dermatomes: Testing Sensory Nerve Roots

A dermatome is the skin area supplied primarily by a single spinal nerve root. Dermatomes are tested with light touch and pinprick, comparing side to side and level to level, using consistent anatomical landmarks:

The saddle distribution (S2-S4) is a critical exam landmark: saddle anesthesia combined with bowel or bladder dysfunction and bilateral leg weakness defines cauda equina syndrome, a surgical emergency that must never be treated as routine radiculopathy.

A key discriminator tested repeatedly on Part III is dermatomal versus peripheral nerve sensory patterns. A dermatomal (nerve root) lesion produces a broad band of sensory change that crosses multiple peripheral nerve territories, following the segmental map above. A peripheral nerve lesion instead produces sensory loss confined to that specific nerve's own cutaneous territory, which typically does not correspond neatly to any single dermatome. Recognizing this distinction is what separates a radiculopathy from a focal neuropathy or nerve entrapment on the exam.

Deep Tendon Reflexes (DTRs)

DTRs are graded 0 to 4+: 0 = absent (areflexia), 1+ = diminished (hyporeflexia), 2+ = normal, 3+ = brisk (hyperreflexia), and 4+ = very brisk with sustained clonus. A depressed or absent reflex generally localizes to that specific nerve root or a peripheral nerve/lower motor neuron problem, while an exaggerated reflex with spread to adjacent muscles suggests loss of descending upper motor neuron inhibition.

Upper Motor Neuron vs. Lower Motor Neuron Lesions

Recognizing this table cold is essential: a vignette describing spasticity, hyperreflexia, and a positive Babinski points toward a central lesion (spinal cord, brain), while flaccidity, hyporeflexia, fasciculations, and focal atrophy point toward a nerve root, plexus, peripheral nerve, or anterior horn cell problem.

Pathological Reflexes

• Babinski sign: Stroke the lateral plantar surface of the foot from heel to toes. Positive = extension of the great toe with fanning of the other toes. Normal in infants under roughly 1-2 years (immature corticospinal myelination); a pathological upper motor neuron sign in any older child or adult.
• Hoffmann's sign: Flick the distal phalanx of the patient's flexed middle finger downward. Positive = reflexive flexion/adduction of the thumb and index finger. Suggests a cervical cord upper motor neuron lesion.
• Clonus: Rapidly and forcibly dorsiflex the ankle and sustain the pressure. Positive = rhythmic, oscillating contraction/relaxation of the calf muscles (typically defined as sustained beyond 3-4 beats).
• Oppenheim's sign: Firmly stroke down the anteromedial border of the tibia. Positive = the same extensor toe response as Babinski; used as an alternate elicitation method.
• Chaddock's sign: Stroke the skin below the lateral malleolus around to the lateral foot. Positive = the same extensor toe response as Babinski; useful when the plantar surface itself is too sensitive or ticklish to test directly.

Sensory Testing Modalities and Their Pathways

Pain (pinprick) and light touch/temperature travel primarily through the spinothalamic tract (the anterolateral system), which crosses to the opposite side of the spinal cord within one or two levels of entry. Vibration and proprioception (joint position sense) travel through the dorsal (posterior) columns, ascending on the same side and crossing only much higher, in the medulla. This anatomical split explains dissociated sensory loss patterns seen in certain cord lesions — for example, Brown-Sequard syndrome (cord hemisection) produces ipsilateral loss of vibration and proprioception together with contralateral loss of pain and temperature below the level of the lesion, because the two pathways cross the midline at very different levels.

Two-point discrimination tests higher-order, cortical sensory integration and fine discrimination rather than a single peripheral pathway, and is typically reduced earliest in peripheral neuropathies and dorsal column lesions, before cruder touch sensation is lost.

Bringing It Together

Part III neurological vignettes are built to be solved by combining findings, not by any single isolated sign. A patient with weak resisted wrist extension (C6 myotome), diminished thumb/index sensation (C6 dermatome), and a depressed brachioradialis reflex (C6) all point to the same C6 nerve root, and the exam expects the candidate to recognize that convergence rather than analyzing each finding as if it belonged to a different level.