Neuromuscular disorders

Question 1

History Taking

Answer 1

• defects in neurological action - motor (weakness), sensory (peripheral sensory nerve disorders), autonomic (postural hypotension)
• anatomical distribution (legs vs arms, prox. vs distal, symm vs asymm, specific nerve roots or root distrib.)
• Temporal course (disease course, age of onset, daily variability/fatigue)

Question 2

Examination

Answer 2

• tone
• power
• Coordination
• Reflexes
• Sensation

Question 3

What do we see in musclar disease (myopathy)?

Answer 3

• weakness - usually proximal
• weakness leads to wasting
• reflexes are normal (except in a severely wasted muscle)
• Sensory - normal
• Creatinine kinase will be high in blood
• Electromyography - gives myopathic picture

Question 4

Is it a genetic disease?

Answer 4

- family history?
>family members may be affected but not manifesting or diagnosed yet
>De novo mutations
>pentrance
- slow progression over years
- limb deformities?

Question 5

What are some examples of genetic myopathies?

Answer 5

• muscular dystrophies
• Duchenne
• Becker
• Myotonic
• Facioscapulohumeral

Question 6

Duchenne muscular dystrophy

Answer 6

• mutation in dystrophin gene (Xp21)
• onset age - 3-5 (start having difficulty walking)
• proximal weakness
• lose walking in early teens
• problems - scoliosis, resp. failure, cardiomyopathy
• usually die in 20s
• Get pseudo-hypertrophy of the calves (actually fatty deposits)

Question 7

Duchenne’s - What is Gower’s manouever?

Answer 7

• when they try to stand up, they have profound weakness around the hips and so have to use arms to prop themselves up, then use knees - rather than just using hip flexors

Question 8

Duchenne’s - Genetics

Answer 8

• dystrophin one of the largest genes
• gives the linkage between sarcolemmal cytoskeleton and ECM
• Deletions with frameshift = duchenne
• Deletions without frameshift = Becker

Question 9

Duchenne vs Becker

Answer 9

• Duchenne = frameshift deletion leads to non-functional protein
• Becker = non-frameshift deletion leads to reduced function protein
• Becker’s is much milder

Question 10

Give some examples of other myopathies

Answer 10

• Acquired inflammatory myopathies - polymyositis, dermatomyositis, inclusion body myositis
• endocrine, GI, paraneoplastic, renal, toxic, infections, iatrogenic (steroids)

Question 11

Neuromuscular junction disorder

Answer 11

- inherited
> Congenital myasthenic syndromes (caused by mixture of diseases)
- acquired
> myasthenia gravis
>botulism (mimics MG)

Question 12

What is myasthenia gravis?

Answer 12

• droopy eyelids
• difficulty raising arms, breathing, swallowing
• Caused by antibodies which block AChR

Question 13

Neuromuscular junction disorder characteristics

Answer 13

• fatigable weakness
• usually proximal then distal
• extraocular muscles and face often involved (droopy eyelids and blurred vision)
• Normal reflexes and sensations
• Normal creatinine kinase
• electromyography - decrement on repetitive stim.

Question 14

Neuropathy characteristics

Answer 14

• weakness usually distal, commonly proximal if root or plexus, may be cranial neuropathy (extraocular eye movement and facial nerve)
• Early wasting
• reflexes reduced or absent
• pain may occur from sensory tests
• Creatinine kinase may be elevated slightly
• Electromyography gives a neurogenic picture

Question 15

What is the pattern of disease?

Answer 15

- Anatomical distribution?
> Focal? - mononeuropathy, Radiculopathy
>multifocal? - multiple mononeuropathies, polyneuropathy
- Symmetrical
>proximal?
>distal?

Question 16

Type of motor affected?

Answer 16

• motor
• sensory - large fibres (Aa, Ab - JPS,vibration), small fibres (Ad, C - pain,temp)
• autonomic - small fibres

Question 17

Pathological clasification

Answer 17

• Axonal neuropathies (80% with over 80 causes)
• Demyelinating neuropathies (20% with about 20 causes - mostly genetic or inflammatory)
• mixed
• can only be classified in biopsy or nerve conduction study

Question 18

What is ulnar nerve palsy?

Answer 18

• all intrinsic muscles of the hand except LOAF muscles
• lose grip, tingling, pain, hand weakness
• leads to claw deformity

Question 19

What is mononeuropathy?

Answer 19

• Traumatic
• entrapment of:
  > median nerve = carpal tunnel
  > ulnar nerve (elbow or wrist) = handlebar neuropathy
  > radial nerve = saturday night palsy, handcuff neuropathy
  > common peroneal nerve = foot drop

Question 20

Polyneuropathies

Answer 20

• affect multiple nerves
• acquired
• inflammatory, metabolic/endocrine, from drugs, toxins ot infections

Question 21

What is Charcot-Marie-Tooth disease?

Answer 21

• hereditary polyneuropathy
• commonest genetic neurological disorder
• Prevalence = 1/2500
• Inherited - most common cause is duplication of 17p22.
• presentation - childhood onset, progressive muscle and sensation loss, distal wasting, pes cavus (high arched feet)
• CMT1 - demyelinating ~60%
• CMT2 - axonal ~30%
• ~10% mixed

Question 22

Plexopathy

Answer 22

• usually post-infective/traumatic

- constellation of symptoms dependent on location and extent of plexopathy

Question 23

Erb’s palsy

Answer 23

• upper trunk of brachial plexus - lose C5/C6 muscles
• arm adducted (abducters weak)
• Elbow extended (flexors weak)
• wrist pronated (supinators weak)
• wrist flexed (extensors weak)

Question 24

Radiculopathy - nerve roots

Answer 24

• common causes = arthritis, prolapsed disc
• radicular (nerve root) pain
• if severe > weakness and wasting

Question 25

Motor neurone disease

Answer 25

- Primary degeneration of motor neurons in the CNS and PNS - can be genetic or acquired - affects MNs in anterior horn and motor strip - affects control of all voluntary muscles except ocular and bladder - fatal within 5 years