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 palsies. In 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

Bell’s Palsy [Facial Nerve Palsy] (OSCE Guide)

Facial nerve palsy can be either UMN type or LMN type. It can be unilateral or bilateral. The most common scenario would be LMN type unilateral facial nerve palsy (Bell’s Palsy) you would encounter at the exam. LMN lesions affect both upper & lower parts of the face in contrast to the UMN lesions.

You should be thanking your destiny if you got Bell’s palsy as one of your cases at the exam because it is one of the easiest short cases you would ever get at the neurology station. Though it is a pretty straightforward case, just diagnosing Lower Motor Neuron (LMN) type of facial nerve palsy may not be enough for you to acquire higher marks. Always think about the possible aetiology & try to localize the site of the lesion whenever possible once you detect LMN type of facial nerve palsy.

The general instruction would be to “Examine the lower motor crannial erves” or “Examine the motor cranial nerves”. Always follow the instruction of the examiner.

BELL’S PALSY – EXAMINATION

DIAGNOSE BELL’S PALSY

• Facial asymmetry (involving affected half of the face – both upper & lower parts)
• Delayed / Absent Blinking of one eye (affected side)
• Loss of facial expressions
• Drooping of the corner of the mouth (affected side)
• Deviation of the mouth to the opposite side when the patient is asked to clench teeth.
• Widened palpebral fissure (affected side)
• Flattened nasolabial fold (affected side)

LOCALIZE THE LEISON

1. At Parotid gland (Parotid Neoplasm)

• Palpate the gland enlargement (Neoplasia).
• Elicit parotid tenderness (Parotitis).
• Look for surgical scars on the parotid gland (Previous Surgery).

2. At External Acoustic Meatus (Ramsey Hunt Syndrome, Infection)

• Look for vesicles in external auditory canal & soft palate.
• Look for pus discharge from the ear.

3. At Middle Ear (CSOM, Cholesteatoma)

• Look for hyperacusis – A tuning fork would sound louder in the affected ear.

4. At Internal Acoustic Meatus (Acoustic Neuroma)

• Look for hearing impairment (Associated 8th nerve palsy when entering together with the facial nerve at internal acoustic meatus).

5. At Cerebellopontine Angle (CP angle tumour)

• Associated 5th nerve palsy – Look for ipsilateral facial numbness along with hearing impairment (8th nerve palsy), 6th nerve may also be involved.
• Ipsilateral Cerebellar Signs.

6. At pons (Pontine infarction / Hemorrhage)

• Associated 6th nerve palsy (Lateral Rectus Palsy) of the affected side. Check eye movements.

Facial Nerve Palsy (Bell’s Palsy) – CASE PRESENTATION

This patient is having left side facial asymmetry involving both upper and lower parts of the face. There is absent blinking of the left eye. The mouth is deviated to the right side when an attempt to clench the teeth. There is reduced facial expressions with widened palpebral fissure and flattened nasolabial fold on the left side.

The parotid gland is not enlarged or tender. There is a vesicular rash involving the left external auditory meatus and soft palate. Other cranial nerve examination is unremarkable.

He is having left LMN type Facial nerve palsy secondary to reactivation of Varicella-Zoster Virus; that is Ramsay-Hunt Syndrome.

FREQUENTLY ASKED QUESTIONS

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

Carpal Tunnel Syndrome (OSCE Guide)

The examination of hand for neuropathies is commonly encountered at OSCE stations. One of the most common scenarios would be carpal tunnel syndrome.

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

CARPAL TUNNEL SYNDROME – EXAMINATION

Usually, the command is to examine the hands of the patient, but sometimes you might be given a clue like “This lady presented with tingling sensation in her hands”. The disease is often bilateral.

1. Ask the patient to spread out the hands for you.
2. Look for,
   • Wasting of thenar muscles.
   • Scar of a previous carpal tunnel decompression surgery.
3. Examine the functions of the muscles supplied by the Median nerve.
   • Abductor Pollicis Brevis – Ask the patient to place the dorsum of the hand on a flat surface and lift the thumb towards the ceiling against resistance (Pen touch test).
   • b. Opponens Pollicis – This muscle is usually not tested as it may also be supplied by the ulnar nerve ( an anatomical variation).
4. Examine the sensory distribution.
   • There is an area of sensory loss over the palmar aspect of the lateral three and a half fingers.
   • However, the sensation over the thenar eminence is preserved.
5. Special Signs to elicit,
   • Tinel’s Test – Tap over the flexor aspect of the wrist over the midline. If the patient feels a tingling sensation over the distribution of the median nerve, the test is positive.
   • Phalen’s Test – Ask the patient to flex the wrists maximally and keep for one minute. If the patient feels pain in the hands, the test is considered positive.
6. Try to identify a probable aetiology.
   • Obesity.
   • Hypothyroidism – Goiter? Facial puffiness? Loss of lateral third of eyebrows?
   • Rheumatoid arthritis – Shawn neck deformity? Boutnier’s deformity? Z thumb?
7. Offer assessment of the patient’s quality of life (QOL).
   • Nocturnal and early morning worsening of symptoms.
   • Effects on occupation or activities of daily living (eg: Washing clothes).

PRESENTATION

This patient who presented with tingling sensation of hands has bilateral thenar muscle wasting but there is no wasting of hypothenar eminence or dorsal guttering. There are no visible surgical scars, suggestive of previous carpal tunnel decompression surgery. Her opposition of the thumbs is weak and the pen touch test is positive, but there is no weakness in finger adduction or extension. There is an area of sensory loss over the palmar aspect of the lateral three and a half fingers and no other areas of sensory loss. Tinel’s test and Phalen’s test are positive. So my tentative diagnosis is bilateral Carpal Tunnel Syndrome (CTS) and I would like to assess her functional disability and probable aetiology.

FREQUENTLY ASKED QUESTIONS

Radial Nerve Palsy (Saturday Night Palsy)

Radial Nerve Palsy – Overview

Radial nerve palsy (Saturday night palsy) is one of the common clinical presentations. The radial nerve is one of the three major peripheral nerves of the upper limb. It supplies the extensor aspect of both arm and forearm. It innervates triceps and all the muscles in the posterior aspect of the forearm which are responsible for extension of the elbow and the wrist, fingers, and supination of the forearm.

Radial nerve – Origin, course, and branches

It originates in the axilla as the terminal continuation of the posterior cord of the brachial plexus carrying its all five nerve root values from C5 to T1.

Then it passes posterior to the axillary artery to enter the anterior compartment of the arm crossing the inferior border of the teres major muscle. After a short course, radial nerve leaves the anterior compartment of the arm accompanying the profunda brachii artery to enter its posterior compartment. Here the nerve directly lies on a diagonal groove on the shaft of the mid humerus (Spiral Groove) running from medial to lateral. 

Reaching the lateral side of the arm, it pierces the lateral intramuscular septum to re-enter the anterior compartment of the arm in between brachialis and brachioradialis muscles. Then it enters the forearm passing anterior to the lateral epicondyle of the humerus and immediately divides into two branches, namely deep branch and superficial branch. 

The deep branch of the radial nerve enters the posterior compartment of the forearm piercing the supinator muscle where it is termed posterior interosseus nerve for the remainder of its course. 

Out of the four sensory branches of the radial nerve, three of them arise in the upper arm descends downwards. They are namely, lower lateral cutaneous nerve of the arm, posterior cutaneous nerve of the arm and posterior cutaneous nerve of the forearm. The fourth branch is the terminal continuation of the radial nerve itself as the superficial branch of the radial nerve which is the only branch of radial nerve crosses which the wrist joint.

Innervation

Motor

 The radial nerve itself innervates all three heads of the triceps in the arm and extensor carpi radialis longus and brachioradialis muscles. It supplies the supinator muscle while piercing through it and the remainder of the muscles are innervated by the posterior interosseous nerve.

Sensory

Cutaneous branches of the radial nerve supply the skin of the lower lateral arm, dorsal aspect of the arm, forearm and the lateral three and a half fingers. However, there is a significant overlap of sensory innervation from the adjacent nerves except in the dorsal aspect of 1^st webspace of hand.

Radial Nerve Palsy – Sites of Injury

The clinical presentation of radial nerve palsy is different depending on the site of the lesion. It is susceptible to injury commonly at four sites.

In Axilla

Due to its close relationship to proximal humerus and shoulder joint, the radial nerve is liable for injury in axilla by shoulder dislocation and fractures involving the proximal humerus. It may also be damaged falling asleep one’s hand hanging over the arm of a chair compressing the radial nerve at axilla for a prolonged duration (Saturday night palsy) or by a badly fitting crutch (Crutch palsy). 

The extension of the forearm at the elbow is totally lost as the triceps is denervated completely when the nerve is damaged at the axilla. Obviously, the wrist extensors in the forearm are also paralyzed resulting in wrist drop due to unopposed activity of intact flexor muscles.

As all four of the sensory branches are affected in this case, there will be a widespread sensory loss affecting the lateral aspect of the arm, posterior aspect of arm and forearm and the dorsal aspect of lateral three and a half fingers of the hand and palm.

In Radial Groove

Here the nerve lies directly on the humerus as it winds around it and susceptible for damage in fractures involving midshaft of the humerus.

The forearm extension is only weakened (in contrast to total paralysis) due to triceps’ partially intact innervation. The branches for long head & lateral head of the muscle are given off proximal to the spiral groove resulting in incompletely denervated muscle. Only its medial head loses the nerve supply. There will be wrist drop deformity owing to loss of motor supply to wrist extensors as the deep branch of the radial nerve is affected.

Since the sensory branches to arm & forearm are given off in the upper arm, they remain intact. The only branch to be affected is the superficial branch of the radial nerve which in turn results in sensory loss over the dorsal surface of the lateral three and a half fingers which is more marked over the 1^st webspace.

In Distal Forearm

Here the nerve lies close proximity with the radial neck and can be easily damaged in posterior dislocation of elbow joint and fractures involving the head & neck of the radius.

Even though most of the muscles in the posterior compartment of the forearm are affected which are innervated by the deep branch of the radial nerve, surprisingly the wrist drop deformity does not occur. It is due to intact extensor carpi radialis longus which is innervated by the main branch of the radial nerve itself before its division hence unaffected in the injury. This muscle alone can maintain the wrist in extension though there is some degree of weakness.

As the superficial branch of the radial nerve is unaffected there will be no sensory loss.

At the Neck of the Radius

The superficial branch of the radial nerve can be damaged due to direct trauma causing soft tissue injuries in the forearm such as stabs or lacerations.

The only branch may be involved is the superficial branch of the radial nerve which is purely sensory. The patient will have no motor weakness and there will be sensory loss over the lateral three and a half finger of the affected hand