Neuro Exam Qs Flashcards
What is the difference between medical and surgical third nerve palsy? Name some causes of each
A medical third nerve palsy classically spares the pupil, whereas a surgical third nerve palsy causes pupillary dilation. The pupil is usually sparred in medical causes because the fibres that control the pupil are contained within the outermost layer of the nerve, and are less prone to ischaemia than the inner parts of the nerve. In surgical/compressive causes, the whole nerve is involved.
Medical (classically pupil-sparing), M’s:
Microvascular ischaemia (diabetes)
Migraine
MS/autoimmune disorders
Surgical (classically painful), C’s:
Posterior Communicating artery aneurysm (classic cause)
Cavernous sinus lesion
Cancer (SOL)
Discuss how you would clinically distinguish between an LMN facial nerve lesion and a UMN facial nerve lesion, and comment on why they present differently
An UMN facial nerve lesion spares the forehead, because the nucleus controlling the upper part of the face has bilateral UMN innervation, whereas the lower part of the face has only contralateral UMN innervation.
A LMN facial nerve lesion causes weakness of the whole side of the face, because the LMN innervates the whole side. If this nerve is damaged, there is no innervation at all.
Please list three causes of a unilateral facial nerve lesion, and two causes of bilateral facial nerve lesions.
Causes of a unilateral facial nerve lesion:
- Bell’s palsy
- Ramsay Hunt syndrome
- SOL (e.g. acoustic neuroma, facial nerve tumour, meningioma)
- Lyme disease
- Nerve infiltration (TB, sarcoidosis, lymphoma)
- Parotid tumour/surgery
Causes of bilateral facial nerve lesions:
- Lyme disease
- Sarcoidosis
- Guillain-Barré syndrome
- Amyloidosis
What are the nerves involved in the gag reflex?
Afferent = CN 9 (sensory Glossopharyngeal)
Efferent = CN 10 (Motor vagus)
Describe the difference between afferent and efferent pupillary defects?
Afferent defect (sensory defect of the optic nerve) = pupils are symmetrical but when light is shone in the affected eye, neither pupil constrict = CN2 lesion
Efferent defect (motor, oculomotor nerve) = affected pupil is persistently dilated, whilst other is reactive to light being shone in either eye = CN3 lesion
What would be your differential diagnosis for a sensorimotor polyneuropathy?
Use ABCDE to list causes of a sensorimotor polyneuropathy:
- Alcohol
- B12/thiamine deficiency
- Charcot-Marie-Tooth, Carcinomas (paraneoplastic)
- Diabetes, Drugs (e.g. TB drugs, metronidazole/nitrofurantoin, vincristine/cisplatin, amiodarone)
- Every vasculitis (e.g. SLE, RA, polyarteritis nodosa) and some infections (e.g. herpes zoster, HIV, leprosy, syphilis)
Which conditions may result in a unilateral upper motor neurone lesion?
Work down (brain to cord):
Intracranial – stroke, SOL → hemisensory loss
Brainstem – stroke, SOL → may be crossed signs
Spinal cord – MS, infarct/haemorrhage, SOL, disc prolapse, trauma, syringomyelia, congenital → sensory-level/segmental sensory loss
What are the causes and clinical features of a Brown-Sequard syndrome?
A Brown-Sequard syndrome is caused by damage to one half of the spinal cord. It is characterised by loss of power and proprioception on the ipsilateral side, and loss of pain and temperature on the contralateral side.
This is because the spinothalamic tract decussates in the spine, whereas the other tracts decussate in the brainstem.
Clinical features of UMN lesion?
- Increased tone
- Spasticity
- Weakness
- Brisk reflexes, upgoing plantar reflex (babinski reflex)
Clinical features of LMN lesion
- Wasting and fasciculation
- Hypotonia
- Weakness
- Reduced reflexes
Nerve root when assessing power: Hip flexion?
L1 / L2
Nerve root when assessing power: Hip extension?
L5 / S1
Nerve root when assessing power: Knee flexion
L5 / S1
Nerve root when assessing power: Knee extension
L3 / L4
Nerve root when assessing power: Ankle dorsiflexion
(pushing ankle up)
L4
