Oculomotor Nerve Palsy (OSCE Guide)

6/03/2020

Oculomotor Nerve Palsy (OSCE Guide)

Oculomotor nerve (CN III) palsy is a common short case at the neurology station and it is usually evident with a distant because of unilateral complete ptosis.

As the name implies, the oculomotor nerve supplies the majority of the extraocular muscles apart from Lateral Rectus (supplied by VI nerve) and Superior Oblique (supplied by IV nerve). In addition, it supplies Levator Palpebrae Superioris muscle of upper eyelid and Sphincter Pupillae muscles which is responsible for pupillary constriction. This innervation is vital for understanding the clinical signs in III CN palsy, namely ptosis (often complete), dilated pupil and ophthalmoplegia.

There are two clinical entities, “Medical” and “Surgical” third nerve palsiesIn a case of Surgical third nerve palsy, you are expected to do an extended examination to clinically locate the site of nerve compression to obtain full allocated marks.

OCULOMOTOR NERVE PALSY – EXAMINATION

DIAGNOSE THE THIRD NERVE PALSY

1. Unilateral Ptosis (Often Complete Ptosis)

This is obvious! You have to manually and gently elevate the upper eyelid when you carry on your examination to look for ophthalmoplegia.

2. Divergent Strabismus

Due to Medial Rectus palsy and unopposed action of Lateral Rectus supplied by the VI nerve.

In fact, the eye will be “Down & Out” because the Superior Oblique (supplied by IV nerve) is unantagonized by the paralyzed Superior Rectus, Inferior Rectus and Inferior Oblique muscles.

3. Ophthalmoplegia

Impaired adduction of eye due to paralysis of Medial Rectus.

4. Mydriasis (Dilated Pupil)

Due to the involvement of the parasympathetic nerve supply from the Edinger-Westphal nucleus. These fibers are located superficially, thus in external compression, they are affected first, making the pupil dilated.

  • Surgical Third Nerve palsy – When Pupil is affected (dilated)
  • Medical Third Nerve palsy – When pupil is spared.
5. Loss of Accommodation Reflex

Due to the involvement of the Ciliary muscle.

LOCALIZE THE LESION

This is especially important when the pupil is affected (Surgical Third Nerve palsy) which would indicate an external compression of the Oculomotor nerve somewhere along its cause. You should do a targeted neurological examination to find out the possible location of the nerve.

1. At Midbrain – Contralateral Hemiplegia (Weber Syndrome)

Due to the involvement of Corticospinal tracts usually due to a Brainstem infarction.
Sometimes associated with tremor and involuntary movements (Benedikt Syndrome) when the red nucleus of the midbrain is involved.

2. After emerging from Midbrain – Isolated Surgical Third Nerve Palsy

It is seen without the involvement of other adjacent nerves. Here, the nerve is in close relationship with the posterior communicating artery and can be compressed with aneurysms of the above-mentioned artery.

3. At Cavernous Sinus – Associated IV & VI Nerve Palsies and Sensory Loss in V1 & V2.

At the cavernous sinus the oculomotor nerve is closely related to Trochlear and Abducens nerves and ophthalmic and Maxillary branches of Trigeminal nerves. Those nerves are affected together in case of Cavernous sinus thrombosis.

4. At Orbit – Associated IV & VI Nerve Palsies and Sensory Loss in V1 (NOT V2).

At the orbit, the Maxillary branch of the Trigeminal nerve is not in close relationship with the Oculomotor nerve, hence unaffected. It can occur in intraorbital cellulitis.


OCULOMOTOR NERVE PALSY – CASE PRESENTATION

This patient has right complete ptosis and a divergent strabismus at neutral position. The right eye movements are impaired especially the adduction and it is fixed in down & out position. The right pupil is fixed and dilated. The accommodation reflex of the right eye is lost.

On my extended limited neurological examination, there are no associated IV or VI nerve palsies on the right side. There is no sensory deficit over the areas supplied by the maxillary and ophthalmic divisions of the Trigeminal nerve. The patient is having left hemiplegia. There are no hand tremors or involuntary movements.

So, my diagnosis is right oculomotor nerve palsy secondary to brainstem (midbrain) stroke. So, this is a case of Weber Syndrome.


FREQUENTLY ASKED QUESTIONS

1. From where the Oculomotor nerve originate?

It arises from the anterior aspect of the midbrain and originates from two nuclei. • Oculomotor nucleus – Originates at the level of the superior colliculus. • Edinger-Westphal nucleus – supplies parasympathetic fibres via the ciliary ganglion.

2. Describe the anatomical pathway of the Oculomotor nerve?

It originates at the midbrain at the level of superior colliculus —> passes between superior cerebellar and posterior cerebral arteries —> pierces the dura matter anterior and lateral to the posterior clinoid process —> transverses the cavernous sinus —> divides into two branches (Superior and inferior) at the orbit.

3. What are the structures supplied by the Oculomotor nerve?

◦ Superior branch supplies the superior rectus and levator palpebrae superioris. ◦ Inferior branch divides into three divisions and supplies to medial rectus, inferior rectus, inferior oblique and ciliary ganglion (Sphincter pupillae & Ciliary muscle)

4. What are the eponymous syndromes associated with oculomotor nerve palsy?

1. Weber Syndrome – Third nerve palsy + Contralateral Hemiplegia 2. Benedikt Syndrome – Third nerve palsy + Contralateral Involuntary Movements

5. What are the causes of oculomotor nerve palsy?

1. Brainstem Tumours 2. Brainstem Strokes (Ischemic/ Haemorrhagic) 3. Brainstem Demyelination 4. Cavernous Sinus Thrombosis 5. Tentorial Herniation 6. Posterior Communicating Artery Aneurysms 7. Superior Orbital Fissure Lesions 8. Subacute Meningitis 9. Mononeuritis Multiplex (in Diabetes)

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Ulnar Nerve Palsy (OSCE Guide)

ulnar_nerve_palsy
1/03/2020

Ulnar Nerve Palsy (OSCE Guide)

The examination of hand for neuropathies is commonly encountered at OSCE stations. Ulnar Claw-hand is a very characteristic finding in Ulnar nerve palsy.

Firstly, introduce yourself and get consent before you proceed to examine the patient.


ULNAR NERVE PALSY – EXAMINATION

Given below is a targeted examination for Ulnar nerve palsy. But remember to examine other nerves (Median & Radial) to exclude multiple nerve involvement.

  1. Ask the patient to spread out the hands for you and try to spot diagnose the “Ulnar claw hand” (Clawing of the medial two fingers of the hand).
  2. Inspect carefully both the palmar and dorsal aspect of the hands and look for,
    • Wasting of hypothenar eminence (compare with the other side).
    • Dorsal guttering (due to wasted Interossei muscles) – Palpate the 1st finger web where the wasting is often obvious.
  3. Examine the functions of the muscles supplied by the Ulnar nerve.
    • Palmar Interossei – Ask the patient hold a card between two fingers while you attempt to pull it away using the same two fingers.
    • Dorsal Interossei – Ask the patient to keep the hand on a flat surface and spread out the fingers against resistance.
    • Adductor Pollicis – Ask the patient hold a paper between the thumb and the radial aspect of the index fingers while you attempting to pull it away. Flexion of the terminal phalanx of the thumb to hold the paper indicates a positive Froment’s sign.
  4. Examine the sensory distribution.
    • High lesions – There is an area of sensory loss over both palmar & dorsal aspects of the medial side of the hand and medial one and half fingers.
    • Low lesions – There is an area of sensory loss only over the palmar aspect of the medial side of the hand and medial one and half fingers.
  5. Try to identify a probable aetiology.
    • Look for depigmented anaesthetic patches and Ulnar nerve thickening at the elbow (Leprosy).
    • Look for scars on the forearm (trauma).
  6. Offer to assess the patient’s quality of life.

PRESENTATION

There is marked clawing of the ring and little fingers of the right hand and there is wasting of hypothenar eminence with dorsal guttering, but the thenar eminence is not affected. The actions of palmar and dorsal interossei are impaired and Froment’s sign is positive.

The opposition of the thumb and finger extension is intact. There is an area of sensory loss over the palmar aspect of the medial side of the hand and medial one and half fingers. There is no hypopigmented patches or ulnar nerve thickening and there are no visible scars on the forearm.

So my tentative diagnosis is right-sided Ulnar nerve palsy, probably a lower lesion.



FREQUENTLY ASKED QUESTIONS

1. What is “Clawing”?

It is the hyperextension of the metacarpophalangeal joints and flexion of proximal and distal interphalangeal joints.

2. Why does it occur?

It is due to paralyzed Interossei and Lumbricals with unopposed action of long flexors and extensors.

3. What is “Ulnar claw hand”?

The clawing is only obvious in medial two fingers (Because lateral two Lumbricals which are supplied by the median nerve are spared).

4. What is the “Ulnar paradox”?

Surprisingly, high division of the ulnar nerve (anywhere hand’s breadth above the wrist) causes less clawing than the lower lesions.

5. What is the anatomical basis of the Ulnar paradox?

In higher lesions the innervation to the medial half of Flexor Digitorum Profundus is also lost, causing less intense flexion of the fingers.

6. How do you differentiate?

From the degree of clawing and the area of sensory involvement (see examination).

7. What are the muscles that are innervated by the Ulnar nerve?

1. Flexor Carpi Ulnaris.
2. Medial half of Flexor Digitorum Profundus.
3. All Palmar Interossei.
4. All dorsal Interossei.
5. 3rd & 4th Lumbricals.
6. Adductor Pollicis

8. What is the basis of Forment’s sign?

The patient tries to compensate for the ‘lost’ adduction of the thumb by flexion of it (with Flexor Pollicis Longus which is supplied by the Median nerve).

9. What are the causes of Ulnar nerve palsy?

1. Leprosy (often bilateral).
2. Laceration over the wrist or anywhere along its course.
3. Fracture medial epicondyle.
4. Dislocation of elbow.
5. Cubital tunnel syndrome.
6. Degenerative arthritis.
7. Malunion of fractures of the lower end of the humerus (Tardae Ulna nerve palsy).

10. What are the surgical options for Ulnar nerve palsy you know of?

1. Ulnar nerve decompression.
2. Ulnar nerve anterior transposition.
3. Medial epicondylectomy.

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