Limb neuropathies

Question 1

What is carpal tunnel syndrome?

Answer 1

Carpal tunnel syndrome (CTS) is a collection of symptoms and signs caused by compression of the median nerve in the carpal tunnel.

Question 2

Epidemiology of carpal tunnel syndrome

Answer 2

• Most common mononeuropathy and entrapment neuropathy
• F>M: smaller wrists but same sized tendons as men
• Usually in those over 30 years

Question 3

Aetiology of carpal tunnel syndrome

Answer 3

• Repetitive stress injury e.g. typing
• Enforced flexion – e.g. Colles’ splint
• Obesity
• Pregnancy
• Underlying inflammatory conditions e.g. rheumatoid arthritis
• Myxoedema
• Diabetic neuropathy
• Acromegaly
• Neoplasms e.g. myeloma
• Benign tumours e.g. lipomas, ganglia
• Amyloidosis
• Sarcoidosis

Question 4

What is carpal tunnel syndrome caused by?

Answer 4

• compression of the median nerve.
• This typically happens as a result of inflammation of the nearby tendons and tissues, which creates local oedema or swelling which increases the amount of fluid in a very tight space, and essentially puts pressure on the median nerve.
• The median nerve and the nine tendons compete for space.

Question 5

What does the pressure initially do?

Answer 5

can cause a dull ache or discomfort in any of the areas of the hand that are innervated by the median nerve. Eventually this discomfort can lead to paraesthesia, which can extend up the forearm.

Question 6

What areas are affected by carpal tunnel syndrome?

Answer 6

The areas that are affected include the thumb, index finger, middle finger, and the thumb side of the ring finger, as they are the areas of skin innervated by the median nerve.

Question 7

In severe situations what else could happen in carpal tunnel syndrome?

Answer 7

• thenar muscles at the base of the thumb, and the abductor pollicus brevis can start to waste away.
• This happens because these muscles are innervated by the recurrent branch of the median nerve which arises from the median nerve after it passes through the carpal tunnel.
• So compression of the medial nerve will affect anything downstream of it.

Question 8

Why is the little finger not affected?

Answer 8

as it is supplied by the ulnar nerve, while the back of the hand is supplied by the radial nerve.

Question 9

Why is the palm unaffected?

Answer 9

as this is supplied by a superficial palmar branch of the medial nerve that is upstream of the carpal tunnel, rather than downstream.

Question 10

Clinical manifestations of carpal tunnel syndrome?

Answer 10

• Pain: worse at night after a day’s use of hands
• Numbness
• Paraesthesia: relieved by hanging hand over bed and shaking it (wake and shake)
• Muscle weakness in the hands
• Tinels, Phalens and Durkans sign: +ve
• Light touch, 2-point discrimination and sweating can be impaired
• DECREASED GRIP STRENGTH BIG ONE

Question 11

Investigations for carpal tunnel syndrome

Answer 11

• Clinical diagnosis based on presentation
• Examination:
  
  • Phalen’s maneuver: flex the wrists are far as possible and hold that position for a minute, this results in numbness in the areas of the hand innervated by the median nerve in people with carpal tunnel syndrome
  • Tinel’s sign: tap the transverse carpal ligament, this reproduces the symptoms of tingling or feelings of pins and needles in areas of the hand served by the median nerve
  • Durkan’s test: manually compressing the carpal tunnel with the thumb for 30 second, to reproduce symptoms of carpal tunnel
• Neurophysiology testing (electromyography): confirm lesion site and severity; can see slowing of conduction velocity in the median sensory nerves across the carpal tunnel

Question 12

What is the common peroneal nerve?

Answer 12

• terminal branch of the sciatic nerve that arises from L4-S2.
• It is also known as the common fibular nerve.
• The nerve arises from the sciatic nerve in the deep posterior thigh and then passes through the popliteal fossa.
• It then passes around the head of the fibula, which is a common site of compression leading to neuropathy.

Question 13

Sensory and moto function of superficial peroneal nerve

Answer 13

• Sensory: skin over the anterolateral aspect of the lower limb and dorsum of the foot
• Motor: muscles in the lateral compartment of the leg (fibularis longus and fibularis brevis)

Question 14

Sensory and motor function of deep peroneal nerve

Answer 14

Sensory: first dorsal webspace (i.e. between the big and second toe)

Motor: muscles in the anterior compartment of the leg (Tibialis anterior, extensor hallucis longus, extensor digitorum longus)

Question 15

Aetiology of common peroneal neuropathy

Answer 15

commonly due to trauma/injury to the knee (e.g. proximal fibular fracture, knee dislocation)

external compression such as a tight splint or cast, habitual leg crossing, or even abnormal positioning during general anaesthesia.

diabetes mellitus or vasculitis.

Question 16

What are the clinical features of common peroneal neuropathy?

Answer 16

characterised by ‘foot drop’ due to weakness of dorsiflexion at the ankle that may lead to the patient ‘catching their toe’ or ‘tripping’ when walking

sensory loss or paraesthesia over the dorsum of the foot and lateral shin. On examination, there is weak dorsiflexion and eversion of the ankle.

Question 17

What is the radial nerve?

Answer 17

continuation of the posterior cord of the brachial plexus (C5-T1).

Question 18

Where is the radial nerve found

Answer 18

Around the mid-humerus is a shallow depression known as the radial groove or spiral groove that the nerve runs along. As the nerve reaches the elbow is wraps around the humerus and passes anteriorly to the lateral epicondyle and through the cubital fossa to give off two terminal branches

Question 19

What are the 2 terminal branches of the radial nerve?

Answer 19

superficial sensory branch and deep motor branch.

Question 20

What does the radial nerve provide sensory innervation fro?

Answer 20

dorsal aspect of the radial (i.e. lateral) three-and-a-half digits of the hand (i.e. thumb, index, middle, and lateral half of ring finger).

Within the arms and forearm, sensory branches are given off that provide innervation for the skin on the posterior and outer surface of the arm and forearm.

Question 21

Which muscles does the radial nerve provide motor innervation for?

Answer 21

Triceps brachii
Extensor carpi radialis longus
Brachioradialis
Anconeus

Question 22

What does the radial nerve pass through to get into the forearm?

Answer 22

As the nerve passes through the cubital tunnel into the forearm it continues as the posterior interosseous nerve that provides innervation to the extensor muscles of the forearm

Question 23

What are the extensor muscles of the forearm that are innervated by the radial nerve (posterior interosseous nerve)

Answer 23

Extensor carpi radialis brevis
Supinator
Abductor pollicis longus
Extensor carpi ulnaris
Extensor digiti minimi
Extensor digitorum
Extensor indicis
Extensor pollicis brevis
Extensor pollicis longus

Question 24

Why is the raidal nerve particularly vulnerable to compression?

Answer 24

wraps around the posterior surface of the mid-humerus along the radial groove also known as the spiral groove. Classic causes of neuropathy here include a mid-humeral fracture or Saturday night palsy.

Question 25

Key presenting feature of radial neuropathy is?

Answer 25

key presenting feature in radial neuropathy is ‘wrist drop’ due to weakness of the forearm extensor muscles.

Question 26

What is saturday night palsy?

Answer 26

classic presentation commonly seen in patients who are heavily inebriated and place their arm over a chair (or another object) for an extended period of time leading to a pressure injury of the radial nerve

Question 27

what posterior interosseous syndrome?

Answer 27

due to compression of the posterior interosseous branch of the radial nerve. This is commonly due to:

• trauma
• repetitive pronation/supination activities
• space-occupying lesions

Question 28

Clinical features of radial nerve neuropathy

Answer 28

• Sensory loss and/or paraesthesia over the dorsum of the hand (may extend up posterior aspect of the forearm)
• Wrist drop
• Weakness in finger extension
• Weakness in brachioradialis (best assessed by testing forearm flexion against resistance with the forearm in a ‘banging the table’ position)

Question 29

What is the ulnar nerve?

Answer 29

continuation of the medial cord of the brachial plexus (C8-T1)

Question 30

Where is the ulnar nerve found?

Answer 30

The ulnar nerve lies medial to the brachial artery in the upper arm. At the elbow, the ulnar nerve passes between the medial epicondyle of the humerus and olecranon of the ulna. Posterior to the medial epicondyle the ulnar nerve is easily palpable.

Question 31

What are the 2 main tunnels that the ulnar nerve runs through that can lead to compression?

Answer 31

Cubital tunnel at the elbow: bordered by the medial epicondyle, olecranon and arcuate ligament (connects two heads of flexor carpi ulnaris)

Guyon’s (ulna) canal at the wrist: a groove between the pisiform carpal bone and the hook of hamate that are joined by the palmar carpal ligament

Question 32

Sensory function of the ulnar nerve

Answer 32

The ulnar nerve provides sensory function to the skin of both the palmar and dorsal aspects of the medial one-and-a-half digits and adjacent palm. In other words, the little finger and medial side of the ring finger.

It also provides sensation to the medial side of the dorsum of the hand.

Question 33

Motor function of the ulnar nerve

Answer 33

The ulnar nerve provides motor innervation to some muscles in the forearm:

• Flexor carpi ulnaris
• Flexor digitorum profundus (medial half)

Question 34

What intrinsic muscles of the hand does the ulnar nerve provide motor innervation for?

Answer 34

Hypothenar muscles: Opponens digiti minimi, abductor digiti minimi, flexor digiti minimi brevis
Interossei muscles
Medial two lumbricals
Flexor pollicis brevis
Adductor pollicis

Question 35

What is ulnar neuropathy often due to?

Answer 35

often due to compression at the elbow or wrist. Compression can occur anywhere along its course due to haematoma, trauma or tumour for example. Non-compressive aetiologies can include diabetes mellitus or vasculitis.

Question 36

Where is the ulnar nerve particularly vulnerable?

Answer 36

particularly vulnerable to compression around where it passes through the cubital tunnel.

The broad term ‘ulnar compression at the elbow’ is used to reflect that the nerve can be compressed anywhere along its course in the region and not just within the cubital tunnel

Question 37

Why might compression occur in the ulnar nerve?

Answer 37

• trauma (e.g. distal humerus fracture),
• prolonged elbow flexion,
• leaning on the elbow,
• osteophyte formation due to arthritis,
• or other mass lesions.

Question 38

What does ulnar neuropathy typically present with?

Answer 38

sensory changes in the distribution of the ulnar nerve with hand weakness due to loss of intrinsic muscle function.

Question 39

What is ulnar neuropathy characterised by?

Answer 39

• Sensory loss and/or paraesthesia: seen over the little finger and medial side of the ring finger
• Hand weakness (loss of dexterity, grip weakness)
• Muscle wasting: seen over the hypothenar eminence and/or interossei muscles
• Claw hand deformity (if severe): usually more pronounced with compression of the wrist

Question 40

What is claw hand?

Answer 40

refers to hyperextension of the 4th and 5th metacarpophalangeal joints with flexion at the interphalangeal joints. This is particularly noticeable when opening the hand and is due to loss of medial lumbrical function.

Question 41

What is ape hand?

Answer 41

failure of thumb opposition and abduction (due to median nerve neuropathy)

Question 42

What is the hand of benediction?

Answer 42

has been attributed to both ulnar and median nerve neuropathies
Ulnar: seen when trying to open the hand. Hyperextension at 4th/5th MCP joints with abnormal flexion in the IP joints
Median: seen when trying to close the hand. Abnormal flexion of the 2nd/3rd fingers

Question 43

Froment’s test for ulnar function

Answer 43

ask the patient to pinch a piece of paper between thumb and index finger. As the examiner pulls the paper away, if there is flexion of the distal phalanx of the thumb this suggests ulnar weakness. This is because flexion of the distal phalanx of the thumb is performed by the median-nerve inverted flexor pollicis longus

Question 44

Wartenbergs test for ulnar function

Answer 44

ask the patient to hold the fingers fully extended and close together (i.e. adducted). If the little finger drifts away this is positive. Due to weakness of the ulnar-nerve innervated third palmar interosseous muscle. Alternatively, ask the patient to pinch a piece of paper between the little finger and ring finger. The examiner should then attempt to pull the piece of paper away

Question 45

Michael is a 22-year-old male who is rushed into the emergency department after being stabbed several times in the back by a knife. You complete a full neurological examination which reveals left-sided loss of fine touch and vibration sensation, as well as right-sided loss of pain and temperature sensation. Which tract has been injured to lose fine touch and vibration?

Answer 45

Dorsal columns

The dorsal columns are made up of the gracile fasciculus and cuneate fasciculus, which are responsible for sensory ascending pathways. In stabbing injuries to the back, a patient can be left with Brown-Sequard syndrome which can result in the following;

1. Ipsilateral spastic paresis below lesion
2. Ipsilateral loss of proprioception and vibration sensation
3. Contralateral loss of pain and temperature sensation