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MUSCLE AND NMJ DISORDERS Flashcards

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1
Q

What is a myopathy?

A

A disease of muscle in which the muscle fibres do not function properly, resulting in muscular weakness

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2
Q

Inherited myopathies?

A

Muscular dystrophies
Inherited biochemical defects causing myopathy e.g. glycogen storage diseases, mitochondrial myopathy

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3
Q

Acquired myopathies?

A

Polymyositis and dermatomyositis
Drugs e.g. statins, fibrates, steroids, antipsychotics, colchicine
Infections e.g. HIV, influenza, EBV
Alcoholism abuse
Endocrine disorders - thyroid, parathyroid, pituitary or adrenal dysfunction
Systemic inflammatory conditions - SLE, RA, scleroderma, Sjögren, sarcoidosis
Electrocute imbalance

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4
Q

What is the clinical spectrum of statin-induced myopathy?

A

Myalgia
Myositis
Rhabdomyolysis

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5
Q

Clinical features of statin-induced myopathy?

A

Fatigue
Muscle pain
Muscle tenderness
Muscle weakness
Nocturnal cramping
Tendon pain

Symptoms proximal, generalised and worse with exercise

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6
Q

What is myalgia?

A

Muscle pain

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7
Q

What is myositis?

A

A group of rare inflammatory conditions that cause muscle weakness

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8
Q

Most common types of myositis?

A

Dermatomyositis
Polymyositis

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9
Q

What is dermatomyositis?

A

An autoimmune, inflammatory disorder causing symmetrical, proximal muscle weakness and characteristic skin lesions
May be idiopathic, associated with connective tissue disorders or underlying malignancy

Its polymyositis with skin involvement

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10
Q

Which malignancies is dermatomyositis most commonly associated with?

A

Ovarian
Breast
Lung

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11
Q

Which patients with dermatomyositis are most likely to have an underlying malignancy?

A

If the patient is older
(Screen for underlying malignancy folllowing a diagnosis of dermatomyositis)

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12
Q

Skin features of dermatomyositis?

A

photosensitive erythematous rash
macular rash over back and shoulder
heliotrope rash in the periorbital region
Gottron’s papules - roughened red papules over extensor surfaces of fingers
‘mechanic’s hands’: extremely dry and scaly hands with linear ‘cracks’ on the palmar and lateral aspects of the fingers
nail fold capillary dilatation

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13
Q

Presentation of dermatomyositis and polymyositis?

A

Gradual onset over weeks-months, symmetrical, proximal muscle weakness (tends to be neck, shoulder and pelvis first)
Causes diffiuclties standing from a chair, climbing stairs or lifting overhead
May be myalgia in 33%

Others:
Raynauds
Respiratory muscle weakness, interstitial lung disease
Dysphagia and dysphonia

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14
Q

Investigations for dermatomyositis?

A

Elevated creating kinase
High ESR

Autoantibodies:
ANA - 80% positive
Antibodies to aminoacyl-tRNA synthetases in 30%

Malignancy screen for adults - CT chest/abdomen/pelvis
Electromyograhy and muscle biopsy may be required

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15
Q

Management of polymyositis and dermatomyositis?

A

Physiotherapy and OT to help with muscle strength and function
Corticosteroids

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16
Q

What is Polymyositis?

A

An autoimmune inflammatory condition of muscles
May be idiopathic, associated with connective tissue disorders or malignancy

Dermatomyositis is a variant of the disease where skin manifestations are prominent

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17
Q

Pathophysiology of polymyositis?

A

T-cell mediated cytotoxic process directed against muscle fibres

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18
Q

Age and gender for polymyositis?

A

Middle aged
Female:male 3:1

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19
Q

Investigtaions for polymyositis?

A

Elevated CK
Muscle enzymes e.g. LDH, AST and ALT will also be elevated
EMG and muscle biopsy
Anti-synthetase antibodies

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20
Q

What are muscular dystrophies?

A

Genetic conditions that cause gradual weakening and wasting of the muscles

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21
Q

Types of muscular dystrophies?

A

Duchennes muscular dystrophy
Beckers muscular dystrophy
Myotonic dystrophy
Facioscapulohumeral muscular dystrophy
Oculopharyngeal muscular dystrophy
Limb-girdle muscular dystrophy
Emery-Dreifuss muscular dystrophy

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22
Q

What is Gower’s sign?

A

How children with proximal muscle weakness use a specific technique to stand up from a lying position

They get onto their hands and knees, push their hips back and up and then shift their weight backwards and transfer their hands to their knees
Whilst keeping their legs mostly straight they walk with their hands up their legs to get their upper body erect
This is because the muscles around the pelvis are not strong enough to get their upper body erect without the help of their arms

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23
Q

Management of muscular dystrophy?

A

No curative treatment
Management is aimed at allowing the person to have the highest quality of life for the longest time possible - usually involves OT, PT, medical appliances, surgical and medical management of complications e.g. spinal scoliosis and HF

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24
Q

Cause of Duchenne muscular dystrophy?

A

Defective been for dystrophin (the protein that helps hold muscles together) on the X-chromosome

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25
What pattern of inheritance if Duchennes muscular dystrophy and why?
X-linked recessive This is because it’s caused by defective dystrophin on the X-chromosome
26
Male vs female presentation of duchennes muscular dystrophy?
Female carriers of the condition do not usually notice any symptoms - this is because they have 2 X chromosomes. This means if they have children they have a 50% chance of being a carrier if female or having the condition if male Males will be symptmatic
27
Symptoms and signs of duchennes muscualr dystrophy?
Progressive proximal muscle weakness from 5 years - typically starts around pelvis Usually wheelchair bound by 12 Calf pseudohypertrophy Gowers sign Intellectual impairment in 30%
28
Investigations for duchenne muscular dystrophy?
Raised CK Genetic testing for definitive diagnosis
29
Which heart condition is duchenne muscular dystrophy associated with?
Dilated cardiomyopathy
30
Prognosis of duchenne muscular dystrophy?
most children cannot walk by the age of 12 years patients typically survive to around the age of 25-30 years Main cause of death is cardio-respiratory failure
31
How can we slow the progression of duchenne muscular dysophy?
Steroids may improve muscle strength and function for 6 months-2 years Ataluren is a newer med that can be given to children 2 or older who can walk Creative supplementation can improve muscle strength
32
What type of mutation occurs in duchenne muscular dystophy?
Frameshift mutation in the dystrophin gene resulting in 1 or both of the binding sites being lost
33
What type of mutation occurs in Becker muscular dystophy?
Non-frameshift insertion in the dystrophin gene resulting in both bindings sites being preserved = a milder form than duchenne as dystrophin minatians some of its function
34
Important features of Beckers muscular dystrophy?
Clinical symptms and signs develop after 10 years of age Intellectual impairment is much less common than beckers muscular dystrophy Some patients require wheelchairs in late 20s or 30s, whilst others can with with assistance into later adulthood Often live into their 40s or beyond
35
What is myotonic dystophy? Presentation?
A genetic condition causing progressive msucle weakness and wasting, prolonged muscle contractions, cataracts and cardiac arrhythmias Presents in adulthood
36
What is facioscapulohumeral muscular dystrophy? Presentation?
A muscular dystrophy that presents in childhood Causes weakness around the face that progresses to the shoulders and arms A classic initial symptom is sleeping with their eyes slightly open and weakness in pursing their lips e.g. unable to blow their cheeks out without air leaking from mouth
37
What is oculopharyngeal muscular dystrophy? Presentation?
A muscualr dystrophy that usually presents in late adulthood with weakness of ocular muscles and pharynx Typically presents with bilateral ptosis, restricted eye movement and swallowing problems It can affect the muscles around the limb girdles to a varying degree
38
How does limb-girdle muscular dystrophy present?
In teenage years with progressive weakness around the hips and shoulder (limb girdles)
39
How does emery-Dreifuss muscular dystrophy present?
Presents in childhood with contractures, most commonly in the elbows and ankles This shortening of muscles and tendons restricts the range of movement in limbs Patients also suffer with progressive weakness and wasting of muscles, starting with upper arms and lower legs
40
Structure of muscles
Each muscle is surrounded by the epimysium Within each muscle, fascicles (bundles of muscle fibres) are bound together by the perimysium Each muscle fibre is surrounded by endomysium
41
What is the synaptic end bulb?
The nervous system component of the neuromuscular junction - its where the tip of the axon terminal enlarges and terminates close to the muscle fibre
42
What is the motor end plate?
The muscular component of the neuromuscular junction
43
Neurotransmitter for neuromuscular junctions?
Acetylcholine
44
Outline how transmission of ACh across the synaptic cleft occurs?
ACh is stored in vesicles in synaptic end bulb As the electrical signal approaches the synaptic end bulb it stimulates the inflow of Ca2+by opening voltage-gated channels in the cell membrane of the neurone The increase of Ca2+ causes synaptic vesicles to move towards and fuse with the neuron’s cell membrane. Once fused, synaptic vesicle exocytose the ACh into the synaptic cleft ACh then moves across the cleft towards the motor end plate of the muscle fiber The binding of 2 molecules of ACh to an acetylcholine receptor open the ion channel in the receptor and allows influx of Na+ into the muscle fibre This initiates an action potential that travels towards the ends of the muscle fibre to cause contraction
45
What is lambert-Eaton myasthenic syndrome?
An autoimmune condition affecting the neuromuscular junction
46
Cause of lambert-Eaton syndrome?
Most commonly it occurs with small cell lung cancer, and to a lesser extent, breast and ovarian cancer as a paraneoplastic syndrome It may occur independantly as an autoimmune disorder
47
Pathophysiology of Lambert-Eaton syndrome?
Antibodies against voltage-gated Ca2+ which target and damage the calcium channels in presynaptic membranes of the neuromuscular junctions This means less ACh can be released into the synapse = weaker signal and reduced muscle contraction
48
Presentation of Lambert-Eaton syndrome?
Proximal muscle weakness but repeated muscle contraction leads to increased muscle strength Limb-girdle weakness Reduced or absent reflexes Autonomic symptoms: blurred vision, dry mouth, impotence, difficulty micturition
49
Diagnosis of Lambert-Eaton syndrome?
Nerve conduction studies to show after exercise, muscle action potentials increase Chest CT to look for lung cancer
50
Management of Lambert-Eaton syndrome?
Treating underlying malignancy if present Immunosuppression e.g. prednisolone or azathioprine 3,4-diaminopyridine is being trialled IV immunoglobulin therapy and plasma exchange may also be beneficial
51
What is myasthenia gravis?
An autoimmune disorder resulting in insufficient functioning acetylcholine receptors Causes muscle weakness that progressively worsens with activity and improves with rest
52
Men vs women prevalence of myasthenia gravis?
Typically affects women under 40 more and men over 60 more Overall women:men 2:1
53
Antibodies in myasthenia gravis?
Antibodies to acetylcholine receptors in up to 90%
54
Associated disorders to myasthenia gravis?
Thymomas - 15% Autoimmune disorders e.g. pernicious anaemia, autoimmune thyroid, SLE, RA Thymic hyperplasia in up to 70%
55
Pathophysiology of myasthenia gravis?
Acetylcholine receptor antibodies bind to postsynaptic acetylcholine receptors, blocking them and preventing stimulation by acetylcholine The more receptors used during muscle activity, the more they become blocked With rest, receptors are cleared and symptoms improve The antibodies also activate the complement system which can lead to cell damage at the post synaptic membrane, further worsening symptms
56
Presentation of myasthenia gravis?
Muscle fatigability Diplopia - Extraocular muscle weakness Proximal muscle weakness - face, neck, limb girdle e.g. diffiuclty climbing stairs or raising hands above head Ptosis - eyelid weakness Dysphagia Fatigue in jaw when chewing
57
How can you elicit fatiguability in the muscles?
Repeated blinking will exacerbate ptosis Prolonged upward gazing will exacerbate diplopia on further testing Repeated abduction of 1 arm 20 times will result in unilateral weakness when comparing sides
58
Investigations for myasthenia gravis?
Single fibre electromyography - high sensitvity CT thorax to exclude thymoma CK - will be normal Antibodies to ACh receptors Tensilon test
59
What is tensilon test and why is it not commonly used anymore?
Giving IV edrophonium (a reversible acetylcholinesterase inhibitor). This temporarily reduces the muscle weakness This has a risk of cardiac arrhythmias
60
Management of myasthenia gravis?
Long-acting acetylcholinesterase inhibitors e.g. pyridostigmine Immunosuppression will eventually need to be used in addition. Usually prednisolone - this suppresses production of antibodies Thymectomy - can improve symptoms even in pt without a thymoma
61
What is a myasthenic crisis?
A potentially life-threatening complication of myasthenia gravis that causes an acute worsening of symptoms such as respiratory muscle weakness which can lead to respiratory failure Often triggered by another illness e.g. RTI Pt may require NIV or mechanical ventilation
62
Management of a myasthenic crisis?
Plasmapheresis - removal of plasma which contains the antibodies IV immunoglobulins
63
Exacerbating factors for myasthenia gravis?
Exertion During the day Drugs: Penicillamine Quinidine, procainamide Beta blockers Lithium Phenytoin Antibiotics: gentamicin, macrolides, quinolones, tetracyclines
64
What is congenital myasthenic syndrome?
An inherited neuromuscular disorder caused by defects of several types at the NMJ There are many causes e.g. acetylcholine receptor deficiency or choline acetyltransferase deficiency
65
What causes botulism?
Clostridium botulinum - a gram positive anaerobic bacillus that produces botulinum toxin which blocks release of acetylcholine
66
Where can you get clostridium botulinum from?
Eating contaminated food e.g. tinned food IV drug use
67
Features of botulism?
Fully conscious with no sensory disturbance Flaccid paralysis Diplopia Ataxia Bulbar palsy
68
What is bulbar palsy?
A set of symptoms and signs linked to the impaired function of cranial nerves 9, 10, 11 and 12 Causes tremulous lips, weak and wasted tongue, drooling due to dysphagia, absent palatal movements, dysphonia due to vocal cord paralysis, articulation diffiuclties due to dysarthria
69
What is a myeloradiculopathy?
Disorders that affect the spinal cord and the nerve roots exiting the spinal cord E.g. compression of spinal cord by herniated disc
70
What is a ganglionopathy?
Disorder of the ganglion (collection of nerve cell bodies outside the CNS)
71
Anatomical sites that can cause weakness if disease?
Anterior horn cell Peripheral nerve Neuromuscular junction Muscle
72
Anterior horn cell lesions in general give rise to what symptoms?
Weakness Muscle wasting Fasciculations Can be focal but more typically widespread
73
Where does weakness typically affect in myopathy vs peripheral neuropathy?
Peripheral neuropathy - distal Myopathy - proximal
74
Neuromuscular junction lesions in general give rise to what symptoms?
Fatiguable weakness improved by rest
75
Congenital anterior horn cell disorders
Familial motor neuron disease Familial spinal-muscular atrophy
76
What is poliomyelitis?
An infectious disease caused by a poliovirus of the anterior horn cells Can affect motor cranial nerves A small proportion may go on to develop post-poliomyelitis syndrome years after. Causes muscle fatigue, decreased endurance
77
Why type of nerve disorder does a brachial plexus injury cause (broad term!)?
A polyradiculopathy
78
What is erb’s palsy?
A superior trunk injury (C5 and C6) Occurs in newborns e.g. after traction injuries Causes the water tip position - shoulder adducted and internally rotated with the elbow extended and pronated, wrist flexed
79
What is klumpke’s palsy?
Lower trunk injury (C8-T1) Occurs in newborns usually following traction injury Causes paralysis of intrinsic hand muscles, flexors of risk and fingers = claw hand Causes C8-T1 dermatology distribution numbness Involvement of T1 may result in horners syndrome
80
Axonal vs demyelinating neuropathies on nerve conduction studies
Axonal - reduction in amplitude Demeylinating - reduction in conduction velocity by >50%
81
Types of demyelinating polyneuropathy?
Inflammatory demyelinating polyneuropathy Immune-mediated demyelinating polyneuropathy Paraproteinaemia e.g. myeloma
82
Acute polynueropathies?
Acute inflammatory and immune mediated demyelinating polyneirothy and other types e.g. Guillain barre syndrome Diphtheria Porphyria Toxins e.g. thallium Tick bite Paraneoplastic syndromes - rare
83
Chronic polyneuropathy causes?
Deficiencies e.g. B12 Alcohol Heavy metals and solvents Drug toxicity Uraemia Diabetes Vasculitis Cryoglobulinaemia Sarcoidosis Peripheral vascular disease Lyme disease Carcinomatous meningitis Critical illness neuropathy e.g. in ICU for a long time
84
What is the hanging jaw sign?
Inability to hold the jaw open due to weakness in facial muscles Seen in myasthenia gravis
85
Presentation of steroid induced myopathy?
Symmetrical pelvic girdle muscle weakness Quadriceps wasting May have gait changes e.g. Trendelnburg gait

MUSCULOSKELETAL (13 decks)

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