Neuropathies and Myopathies

Question 1

Which nerve roots are involved in the median nerve and what muscles do they innervate?

Answer 1

Median Nerve C6-T1
Nerve of precision grip innervating the muscles: LOAF two lumbricals, opponene policis, abductor policis brevis and flexor policis brevis.

Question 2

What can cause a palsy of the median nerve?

Answer 2

Causes include carpal tunnel syndrome and wrist injuries.

Question 3

How does a median nerve palsy present?

Answer 3

• At the wrist – wasting and weakness of thenar eminence and sensory loss over the radial 3.5 fingers
• Anterior interosseous nerve lesion – weakness of flexion of the distal phalanx of the thumb and index finger
• Proximal lesions – show combined effects

Question 4

How does an ulnar nerve palsy present?

Answer 4

Ulnar Nerve C7-T1
Presentation – weakness/wasting of the hypothenar eminence. Weakness of medial wrist flexors, interossei (cannot cross fingers), medial two lumbricals (causing an ulnar claw), 5th digit abduction and 4tha and 5th DIP flexion. Sensory loss over medial 1.5 fingers and ulnar side of the hand.

Question 5

How is an ulnar nerve palsy managed?

Answer 5

Management – rest and avoiding pressure, night time soft elbow splinting. Surgery may be helpful if this fails. Causes are entrapment at the elbow, wrist injuries and elbow crutch pressure.

Question 6

How is the radial nerve often damaged?

Answer 6

Radial Nerve C5-T1

Often damaged by compression against the humerus.

Question 7

Which muscles does the radial nerve innervate?

Answer 7

BEAST brachioradialis, extensors, abductor pollicis longus, supinator and triceps.

Question 8

How does a radial nerve palsy present?

Answer 8

Presentation – wrist and finger drop when elbow flexed, and arm pronated. Sensory loss can vary, generally the back of the palm but most reliable site is the anatomical snuff box.

Question 9

What causes axillary nerve palsies?

Answer 9

Causes – fracture/dislocation of head of humerus or brachial neuritis.

Question 10

How does axillary nerve palsy present?

Answer 10

Causes wasting of the deltoid and weakness of shoulder abduction with sensory loss over the regimental badge area.

Question 11

How do brachial plexus palsies often occur?

Answer 11

Cause – trauma, radiotherapy, prolonged weakening of a heavy rucksack, cervical rib, thoracic outlet compression. Often damaged due to poor practice in labour or from pulling a child up a cure/swinging them between parents.

Question 12

How does a phrenic nerve palsy present?

Answer 12

C3, 4 and 5 keep the diaphragm alive. Lesions will cause orthopnoea with a raised hemidiaphragm on CXR.

Question 13

What causes phrenic nerve palsies?

Answer 13

Causes – lung cancer, TB, paraneoplastic syndromes, myeloma, thymoma, cervical spondylosis, thoracic surgery, infections (HZV, HIV, Lyme’s) and muscular dystrophies.

Question 14

What is meralgia paraesthetica?

Answer 14

Lateral Cutaneous Nerve of Thigh L2-L3
Meralgia paraesthetica – lateral burning thigh pain from entrapment under the inguinal ligament. Causes include obesity and tight underclothing.

Question 15

What causes sciatic nerve damage and how does it present?

Answer 15

Sciatic Nerve L4-S3
Damaged by pelvic tumours or fractures to pelvis or femur. Lesions affect the hamstring and all the muscles below the knee (foot drop) with loss of sensation below the knee laterally.

Question 16

How does femoral nerve palsy present and what often causes it?

Answer 16

Wasting of quadriceps with weakness of knee extension. Area of sensory loss is over the quadricep and anterior lower leg. Usually occurs due to diabetic amyotrophy.

Question 17

How is the common peroneal nerve often damaged?

Answer 17

Common Peroneal nerve L4-S1
Originates from the sciatic nerve just above the knee and is often damaged as it winds round the fibular head (trauma and sitting crossed legs).

Question 18

How does common peroneal nerve palsy present?

Answer 18

Signs – foot drop, weak ankle dorsiflexion/eversion, sensory loss over dorsal foot and lateral lower leg. Causes include trauma or compression at fibular neck.

Question 19

How does a tibial nerve palsy present?

Answer 19

Tibia Nerve L4-S3
Originates from the sciatic nerve just above the knee. Lesions lead to an inability to stand on tiptoe (plantarflexion), invert the foot or flex the toes with sensory loss over the soles.

Question 20

What runs through the carpal tunnel?

Answer 20

Median nerve and 9 tendons run through the space called the carpal tunnel in the wrist.

Question 21

What is carpal tunnel syndrome?

Answer 21

Compression is common, especially in women as their wrists are smaller but tendons similar size.

Question 22

How does carpal tunnel syndrome present?

Answer 22

Aching pain in the hand and arm, especially at night
Paraesthesia in the thumb, index and middle finger relieved by dangling/shaking
Sensory loss, weakness and wasting of thenar eminence
Light touch, 2-pointdiscrimination and sweating may be impaired

Question 23

What can trigger carpal tunnel syndrome?

Answer 23

Anything that causes swelling: myxoedema, prolonged flexion, acromegaly, myeloma, local tumours, RA, amyloidosis, pregnancy and sarcoidosis

Question 24

How do you test for carpal tunnel syndrome?

Answer 24

Neurophysiology helps to confirm the lesion site and severity
Maximum wrist flexion for 1min (Phalen’s test) may elicit signs
Tapping over the nerve induces tingling (Tinel’s test)

Question 25

How is carpal tunnel syndrome managed?

Answer 25

Splinting
Local steroid injection
Decompression surgery

Question 26

What would suggest a presentation is as a result of a myopathy rather than a mononeuropathy?

Answer 26

Clinical signs and symptoms in favour of myopathy
• Gradual onset of symmetrical proximal weakness
• Specific muscle groups affected
• Preserved tendon reflexes
• No parasthesia or bladder problems
• No fasciculation

Question 27

What aspects to a presentation can help differentiate the causes of myopathy?

Answer 27

• Rapid onset – toxic, drug or metabolic myopathy or neuropathy
• Excess fatigability – myasthenia
• Spontaneous pain at rest and local tenderness – inflammatory myopathies
• Pain on exercise – ischaemia or metabolic myopathy
• Firm muscles (fat or connective tissue) – pseudo hypertrophic muscular dystrophies

Question 28

How should myopathies be investigated?

Answer 28

CRP, ESR, CK, AST and LDH
EMG – electromyography
Muscle biopsy and genetic testing

Question 29

What are muscular dystrophies?

Answer 29

Group of disease with progressive muscle degeneration and weakness within certain muscle groups. Primary problem usually in the muscle membrane and the muscle may become hard due to fat or connective tissue infiltrate.

Question 30

What is DMD?

Answer 30

Most common dystrophy, X linked recessive, presents at 4yrs of age with clumsy walking, difficulty standing and respiratory failure. Pseudohypertrophy is seen especially in the calves. Will have a high CK.

30% of patients have intellectual impairment. Non-functioning dystrophin. Muscle biopsy for diagnosis.

No treatment, a few live beyond 20yrs but most don’t

Question 31

What is Gower’s sign?

Answer 31

Gower’s sign – child uses arms to stand up from squatted position - indicative of DMD

Question 32

What is Becker’s Muscular dystrophy?

Answer 32

Similar to Duchenne’s but with milder symptoms, at a later age and with a better prognosis. Much less common to have intellectual impairment. Autosomal Dominant, partially functioning dystrophin. Muscle biopsy for diagnosis.

Question 33

What is facioscapulohumeral muscular dystrophy?

Answer 33

Almost as common as DMD, onset 12-14yrs, presenting with difficulty puffing out cheeks and raising arms above head. Foot-drop, scapular winging and scoliosis. Fewer than 20% need a wheelchair by age 40.

Question 34

What is myotonic dystrophy?

Answer 34

Tonic muscle spasms (myotonia). Long chains of central nuclei can be demonstrated within muscle fibres on biopsy. Two main types MD1 and 2 both due to trinucleotide repeats.

Question 35

Describe DM1 and DM2

Answer 35

DM1 is more common and more severe presenting between 20-40yrs with distal weakness (hand/foot drop), weak sternomastoid and myotonia. Facial weakness and muscle wasting give a long haggard appearance. Also develop cataracts, male frontal baldness, diabetes, testis/ovary atrophy, cardiomyopathy and reduced cognition.

DM2 – distal weakness more prominent and severe congenital form not seen.

Question 36

What is inclusion body myositis?

Answer 36

Spontaneous muscle pain at rest and local tenderness on palpation. This is the most common example occurring usually age >50. Weakness starts in the quads, finger flexors or pharyngeal muscles. Response to treatment is poor and most progress over a decade to require assistance with ADL.

Question 37

What is polymyositis?

Answer 37

Symmetrical, proximal, progressive muscle weakness and autoimmune mediated striated muscle inflammation giving muscle pain and joint pain.

Question 38

What is dermatomyositis?

Answer 38

In Dermatomyositis associated with a Macular lilac purple heliotrope rash around the eyes with associated oedema. Treat with prednisolone.

Can be a paraneoplastic syndrome associated with lung, breast ovary and GI cancers.

Question 39

What causes mostly motor polyneuropathies?

Answer 39

LMN
Can be mostly motor 
•	Guillain Barre syndrome 
•	Charcot Marie tooth 
•	Lead poisoning

Question 40

What can cause a mixed sensory and motor polyneuropathy?

Answer 40

Alcohol abuse

Question 41

What causes a mostly sensory polyneuropathy?

Answer 41

Mostly sensory 
Glove and stocking distribution, burning/numb and progressive*
•	Diabetic neuropathy 
•	Renal Failure
•	Leprosy 

*Whereas mononeuropathies are usually shooting/tingling, dermatomal or asymmetrical and are sudden or progressive

Question 42

How does an obturator nerve palsy present?

Answer 42

Controls thigh adduction and sensation to the medial thigh. Can be damaged in anterior hip dislocation.

Question 43

How does a superior gluteal nerve palsy present?

Answer 43

Involved in Hip abduction and has no sensory input. Can be damaged in misplaced IM injections, hip surgery, pelvic fracture, and posterior hip dislocation. Injury results in positive Trendelenburg sign.