Conducting a CNS Bedside Examination

Also written as CNS exam, Neurological bedside exam.

A systematic bedside approach to assess consciousness, cranial nerves, motor and sensory function, and reflexes in low‑resource settings. Emphasises clinical reasoning, common tropical causes and what to do when investigations are unavailable.

Overview

The CNS bedside exam evaluates the brain and spinal cord in a patient lying in bed, using observation, simple tools and focused questioning. It guides urgent decisions when imaging or labs are limited.

• Four pillars: level of consciousness, cranial nerves, motor/sensory, reflexes.
• Always note the patient’s position, comfort and safety before starting.

Key concepts

Understanding the hierarchy of the nervous system helps you localise lesions and anticipate complications. In low‑resource hospitals, common infectious and vascular causes dominate.

• Cerebral hemispheres – higher functions, focal deficits.
• Brainstem – cranial nerves, vital functions, respiratory drive.
• Spinal cord – motor and sensory level, reflex changes.

Clinical relevance

A well‑performed exam can differentiate meningitis, cerebral malaria, tuberculous meningitis, stroke, and HIV‑related neuropathy, directing urgent therapy even without imaging.

• Altered consciousness + neck stiffness → suspect meningitis; give empiric antibiotics/antimalarials.
• Focal weakness + hypertension in a young adult → consider stroke; arrange urgent CT if possible.
• Progressive lower‑limb weakness with a sensory level → spinal cord compression; arrange urgent MRI or refer.

Exam pearls

Use a consistent sequence: consciousness → cranial nerves → motor → sensory → reflexes → coordination. Document findings precisely to track change.

• AVPU (Alert, Voice, Pain, Unresponsive) for rapid consciousness check.
• Pupillary size, symmetry and light reaction – assess midbrain.
• Gag reflex (CN IX/X) – check before oral medication.
• Motor strength graded 0‑5 in each limb; note any pronator drift.
• Plantar response – extensor (Babinski) suggests upper motor neuron lesion.

Investigations

Select tests that answer the clinical question raised by the exam. When a test is unavailable, rely on bedside clues and empirical treatment.

• Lumbar puncture: Is there meningitis or subarachnoid hemorrhage? CSF cell count, glucose, protein and microscopy guide antimicrobial choice.
• Rapid malaria test (RDT): Does the patient have cerebral malaria? Positive test directs immediate antimalarial therapy.
• Point‑of‑care glucose: Is altered consciousness due to hypoglycaemia? Low result mandates glucose administration.
• CT head (if available): Is there a space‑occupying lesion or bleed before lumbar puncture? Normal scan permits safe LP.

Management

Treat the underlying cause first, then provide supportive care and monitor neurological status closely.

• Empiric ceftriaxone + antimalarial for suspected meningitis in malaria‑endemic area.
• IV artesunate for confirmed cerebral malaria; monitor for seizures.
• Control blood pressure in stroke; avoid nitroprusside in patients with G6PD deficiency.
• Maintain airway, give oxygen, correct glucose, treat seizures with benzodiazepines.

Common mistakes

Errors often stem from skipping steps, misinterpreting reflexes, or overlooking reversible causes.

• Failing to assess blood glucose before attributing coma to CNS disease.
• Assuming a normal plantar response rules out upper motor neuron lesion – early Babinski may be absent.
• Neglecting to check for neck stiffness before lumbar puncture in a possible bleed.

Questions an examiner may ask

• A 28‑year‑old with fever, headache and a stiff neck is confused. What is your next step and why? — Perform a rapid malaria test and point‑of‑care glucose; if negative, start empiric ceftriaxone and arrange lumbar puncture if CT is unavailable.
• During a ward round you find a patient with left‑sided weakness and a GCS of 13. Which lesion localisation is most likely and what additional exam finding would confirm it? — Suggest right cortical stroke; look for right‑sided facial droop and extensor plantar response on the left.
• A patient with known HIV presents with progressive lower‑limb weakness and a sensory level at T8. What is the most urgent investigation and why? — Arrange urgent MRI of the spine (or refer for MRI) to rule out spinal cord compression from TB abscess; delay can cause permanent paralysis.
• You note a patient’s pupils are equal, 4 mm, and react sluggishly to light. What does this tell you about brainstem function? — Indicates possible diffuse brain injury; monitor for deterioration and consider neuroimaging.
• Why is it unsafe to perform a lumbar puncture in a patient with a focal neurological deficit and no CT scan? — The deficit may be due to a mass lesion; LP could precipitate herniation.
• A child with sickle cell disease presents with sudden severe headache and vomiting. What bedside test helps you decide on immediate management? — Check point‑of‑care glucose and perform a rapid malaria test; if both normal, treat as possible vaso‑occlusive crisis with analgesia and hydration while arranging CT if available.
• What is the significance of an extensor plantar response in a patient with altered consciousness? — Suggests an upper motor neuron lesion, often due to cortical or brainstem insult; guides imaging and urgent treatment.
• During examination you find a pronator drift on the right arm. How does this influence your differential? — Indicates subtle upper motor neuron involvement on the right; raises suspicion for left hemispheric lesion even if strength appears normal.

When to seek help

• Sudden loss of consciousness
• New focal neurological deficit
• Severe headache with vomiting
• Seizure lasting >5 minutes or status epilepticus

Quick questions

What does a unilateral dilated pupil indicate?

Possible third‑nerve palsy from uncal herniation; treat as a neurosurgical emergency.

Why is a bedside glucose check essential in any altered‑sensorium case?

Hypoglycaemia is rapidly reversible and can mimic stroke or meningitis.

Can a normal plantar response rule out an upper motor neuron lesion?

No; early lesions may not produce Babinski. Look for other signs such as spasticity.