Diagnostics & Procedures · Topic 8 of 19

Neurologic & Abdominal Exam: Cranial Nerves, UMN vs LMN, Meningeal & Peritoneal Signs

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Assessment · neurologic and abdominal exam

Neurologic & Abdominal Exam: Cranial Nerves, UMN vs LMN, Meningeal & Peritoneal Signs

Reflexes, tone and atrophy split upper from lower motor neuron lesions. Negative Kernig or Brudzinski signs do not exclude meningitis; guarding, rigidity and rebound mean peritoneal irritation.

01 · Localize the lesionUMN hyperreflexia; LMN atrophy, fasciculations

02 · Read the faceSpared forehead: central facial weakness

03 · Peritoneal signsGuarding, rigidity, rebound: peritoneal irritation

Upper or lower motor neuron lesion?

	Upper motor neuron	Lower motor neuron
Reflexes	Hyperactive	Diminished or absent
Tone	Increased	Decreased or absent
Atrophy	Absent (unless prolonged disuse)	Present
Fasciculations	Absent	Present

Motor exam and reflexes

Biceps reflex C5–C6, brachioradialis C6, triceps C7

Finger flexor reflex C8, knee L4, ankle S1

Record any reflex asymmetry

Babinski (great-toe extension, other toes fan): UMN lesion

Sustained ankle clonus: UMN lesion

Normal plantar response: great-toe flexion

Strength 3/5 moves against gravity only, not resistance

Pronator drift detects subtle weakness

Strength grades: 0 no contraction, 1 trace movement, 2 not against gravity, 3 against gravity only, 4 against some resistance, 5 full. Clasp-knife spasticity indicates a UMN lesion; lead-pipe rigidity, uniform through the range of motion and often with cogwheeling, suggests a basal ganglia disorder. Acute severe cord lesions first cause spinal shock (flaccid paresis, hyporeflexia, no extensor plantar response), evolving over days to weeks into spastic paresis with hyperreflexia and clonus.

Cranial nerves

Lower face weak, forehead and eye closure preserved: central

Forehead and eye closure included: peripheral VII lesion

Third nerve palsy: ptosis, diplopia, impaired adduction, vertical gaze

Third nerve palsy, dilated pupil points to aneurysm or transtentorial herniation compression

Third nerve palsy, spared pupil suggests ischemia (diabetes, hypertension)

Corneal reflex tests V sensation and the VII blink

Facial weakness: wisp felt on both sides, blink decreased

Tongue deviates toward a hypoglossal (XII) lesion

Jaw deviates toward a weak pterygoid (V)

Uvula lifts away from the paretic side (IX, X)

Weakness plus abnormal cranial nerve sign strongly suggests brainstem

Long-tract signs indicate an intra-axial lesion

Isolated cranial neuropathies are more often extra-axial

Merck: upper-face paralysis is more likely, not always, from a peripheral lesion than a central one. Occasionally a posterior communicating artery aneurysm spares the pupil. Long-tract signs: spasticity, sensory loss below the neck. Sixth nerve palsy weakens the lateral rectus, impairing abduction, and the eye may sit slightly adducted; causes include nerve infarction, Wernicke encephalopathy, trauma, infection and increased intracranial pressure. Don't over-call: brief fine nystagmus at end-lateral gaze, bilateral absent gag reflex (especially in older adults) and calf fasciculations in older adults can all occur without disease.

Sensory exam: localize the lesion

Spinothalamic tract: pain and temperature

Dorsal columns: position and vibration

Can't stand feet together, eyes closed (Romberg): impaired position sense

Single dermatome or nerve branch loss: root or nerve

Loss below a dermatomal level: spinal cord

Saddle loss: cauda equina, rectal tone (S2–S4) typically lax

Brown-Séquard: ipsilateral paresis, touch, position, vibration loss

Brown-Séquard: contralateral pain and temperature loss

Key sensory points: C6 thumb, T4 nipple line, T10 umbilicus

Key sensory points: L5 dorsum of foot (third MTP joint), S1 lateral heel

Brown-Séquard syndrome is a unilateral cord lesion. Romberg tests lower-limb position sense.

Meningeal signs

Kernig and Brudzinski have low sensitivity

Nuchal rigidity: resistance to neck flexion from meningeal irritation

Negative Kernig or Brudzinski signs do not exclude meningitis

One emergency department study: sensitivity about 55% (Kernig), 53% (Brudzinski) and 84% (jolt accentuation of headache), with specificity about 89–91% for Kernig and Brudzinski. Other series report sensitivity as low as 5%.

Peritoneal signs

Guarding, rigidity and rebound signal peritoneal irritation

Severe pain, lying as still as possible, silent abdomen suggests peritonitis surgical consult

See Acute Abdomen for urgent surgical consultation.

Abdominal patterns

Murphy sign: deep inspiration worsens RUQ palpation pain, halts inspiration

Murphy sign develops within hours in acute cholecystitis

Appendicitis: McBurney point tenderness

Appendicitis, Rovsing: RLQ pain with LLQ palpation

Appendicitis, psoas: pain on passive right hip extension

Appendicitis, obturator: pain on internal rotation of the flexed thigh

Shifting dullness and a fluid wave signal ascites

Ascites below 1500 mL may give no findings: normal exam doesn't exclude it

Bowel obstruction: distention, especially with scars, tympany, high-pitched rushes

That distention, tympany and rushes pattern strongly suggests bowel obstruction. Ecchymoses at the costovertebral angles (Grey Turner sign) or around the umbilicus (Cullen sign) suggest hemorrhagic pancreatitis but are not very sensitive.

Pearl

A forehead that still furrows, with eye closure preserved, means the facial weakness is central.