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Year 4 - PAN > Neurology - Diseases of muscles > Flashcards

Neurology - Diseases of muscles Flashcards

1
Q

3 classes of muscle disease

A
  1. ) Neurogenic
  2. ) Myopathy
  3. ) Disorders of NMJ
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2
Q

What are neurogenic muscle diseases?

A

Muscles diseases caused by damage to muscle innervation

Can occur due to damage to UMNs (brainstem and spinal cord) or LMNs (nerve roots and peripheral nerves)

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3
Q

What is fibre type grouping?

A

Loss of normal mosaic arrangement of muscles fibres due to re-inervation by non damaged motor neurones

In certain long standing neurogenic muscle diseases - e.g. peripheral neuropathy - damage to motor neurones leads to neurogenic atrophy of all fibres innervated by that neurone

Atrophied fibres can be re-inervated by axons from other motor neurones supplying adjacent fibres - this changes the fibre type of muscle

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4
Q

Examples of neurogenic muscle diseases

A
  1. ) Motor neurone disease
  2. ) Spinal muscular atrophy
  3. ) Peripheral neuropathies
  4. ) Misc spinal disorders
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5
Q

Motor neurone disease

A

= Progressive degenerative disease affecting anterior horn cells in the spinal cord

This causes denervation atrophy and LMN signs (i.e. fasciculations and weakness)

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6
Q

What is spinal muscular atrophy and what gene is involved?

A

= common autosomal recessive disorder
It is caused by homozygous loss of the survivor motor neurone gene 1

Present in 4 main forms - types 1-3 all affect infants and children, while type 4 occurs in adults and has slower progression with variable disability

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7
Q

What misc spinal disorders can cause neurogenic muscle disease?

A
  • Poliomyelitis
  • Syringomyelia
  • Degenerative diseases of the vertebral column (e.g. prolapsed disc, osteoarthritis)

All of these diseases affect the anterior horn cells or ventral nerve root

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8
Q

Name the 5 main types of myopathy

A

Myopathy - disease affecting muscles

  1. ) Muscular dystrophies
  2. ) Inflammatory myopathies
  3. ) Congenital myopathies
  4. ) Metabolic myopathies
  5. ) Toxic myopathies
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9
Q

Muscular dystrophy

A

= group of inherited disorders characterised by muscle fibre destruction

Muscle innervation is usually normal

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10
Q

Duchenne muscular dystrophy

A

X linked disorder affecting males
Caused by loss or reduction in the dystrophin gene product - protein normally present between muscle cell membrane and cytoplasm
Loss of dystrophin causes disruption of cell membrane and unregulated calcium influx - muscle damage

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11
Q

What is the usual presentation of Duchenne muscular dystrophy?

A

Normally presents between ages 2-4 years
Proximal muscle weakness + pseudo hypertrophy of the calves
Patients struggle to climb stairs, walking and rising from the floor (children with DMD will often use their hands to “climb up their legs” = Gower’s sign)

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12
Q

What enzyme is raised in DMD?

A

Serum creatinine phosphokinase (CPK) is raised in the early stages of the disease and in female carriers

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13
Q

Prognosis in DMD

A

Most patients die before aged 20 from cardiomyopathy (also occurs as part of the disease)

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14
Q

Why is DMD also called pseudo hypertrophic muscular dystrophy?

A

Based on biopsy findings of DMD:

  • Irregular sized diameter muscle fibres
  • Fibres showing hyaline degeneration with attempts at regeneration
  • Muscle mass replaced by adipose and connective tissue which contributes to pseudo hypertrophy
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15
Q

Becker muscular dystrophy

A

Also an X linked disorder with similarities to Duchenne muscular dystrophy

But onset is later and progress is slower so many patients survive to adulthood

Allelic variant of DMD - involves deletions of p21 region on X chromosome

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16
Q

What is Limb-girdle dystrophy?

A

Also called Erb dystrophy
Rare autosomal recessive disorders
Usually present at 20-40 years with pelvic girdle weakness and later on shoulder girdle

Biopsy findings are similar to DMD

17
Q

Fascioscapulohumeral dystrophy

A

= Rare autosomal dominant disease affecting both sexes equally
Usually presents in childhood with shoulder and facial weakness and characteristic scapular “winging”

Biopsy shows slowly progressive dystrophy with lymphocytic infiltration

18
Q

What is myotonic dystrophy?

A

= Rare autosomal dominant condition caused by unstable CTG repeat in cAMP dependent protein kinase on chromosome 19

19
Q

Presentation of myotonic dystrophy

A

Usually presents between 15-40 with weakness and wasting of facial, pelvic girdle and proximal limb muscles

Myotonia (persistence of muscle contraction after voluntary action has ceased) is common

Patients also exhibit other systemic disorders - e.g. cataract, gonadal atrophy, and diabetes

20
Q

What agents can cause inflammatory myopathy?

A

Muscles can be involved in a number of infections

  • Bacteria - e.g. clostridia, strep
  • Viruses - e.g. coxsackie B
  • Parasites - toxoplasma, trichinella
21
Q

Polymyositis

A

= most common inflammatory disease affecting muscle

Most commonly occurs in adults - F>M
Associated with collagen vascular diseases (e.g. SLE) or cancer

Patients usually present with weakness, pain and swelling of proximal muscles

22
Q

Dermatomyositis

A

= Microangiopathy affecting skin and muscle

Complement deposition causes capillary lysis and muscle ischaemia

23
Q

Treatment of polymyositis and dermatomyositis

A

Muscle injury is caused by clonally expanded CD 8 T cells (biopsy shows lymphocyte and macrophage infiltrate)

Mechanism of antigen sensitivity is unknown

Treat with immunosuppressives (e.g. steroids, azathiaprine)

24
Q

Inclusion body myositis

A

Type of inflammatory myopathy
Most common in elderly patients and resembles polymyositis but does not respond to steroids

Fibres show inflammation and fibrous necrosis with vacuoles and filamentous intracellular inclusion bodies

25
Q

What are congenital myopathies?

A

These are very rare and occur as inherited disorders
Characterised by hypotonia and flaccidity at birth
Many prove fatal

Hypotonia is also associated with cerebral palsy, Downs syndrome and hypothyroidism

26
Q

Metabolic myopathies

A

Muscles involvement occurs in a number of inherited metabolic disorders mostly with other systemic symptoms - e.g. stroke like symptoms and lactic acidosis in mitochondrial cytopathy

2 examples:

i) Malignant hyperthermia - autosomal dominant condition causes abnormal sensitivity to anaesthetic agents causing fatal hyperpyrexia on exposure
ii) Endocrine myopathies

27
Q

What are the 2 patterns of myopathy caused by alcohol?

A
  1. ) Acute alcoholic myopathy - results from bouts of heavy drinking and causes acute fibre necrosis. Myoglobin released from muscles causes AKI
  2. ) Subacute alcoholic myopathy - occurs in chronic alcoholics. It causes proximal muscle weakness and atrophy with selective loss of type 2b fibres
28
Q

Myasthenia gravis

A

Autoimmune disease affecting neuromuscular transmission

Number of post synaptic acetylcholine receptors is reduced and patients have high anti-AChR antibodies

29
Q

What other condition is associated with myasthenia?

A

Thymoma (10% of patients)

30
Q

Clinical presentation of myasthenia

A

Painless muscular weakness by repetitive or sustained contraction

Most commonly affecting face and eyes - bilateral ptosis and diplopia

Dysarthria and dysphagia can occur

Proximal muscles more affected than distal, and upper limbs more affected than lower

31
Q

Examination findings in myasthenia

A

Weakness on sustained contraction is most common

There is no wasting or LMN signs and reflexes are intact

32
Q

How is a patient with myasthenia diagnosed?

A
  • Serum anti-AChR antibody titre
  • Edrophonium (tennsilon test) = short acting acetylcholinesterase inhibitor produces temporary increase in synaptic ACh levels - rapid, transient improvement in clinical features
  • EMG
  • TFTs
  • CT thorax - thymoma
33
Q

What treatment options are available for MG?

A
  1. ) Long acting, oral anti cholinesterase - e.g. pyridostigmine or neostigmine
  2. ) Corticosteroids - alternate day regime should be started at a low dosage as there is a risk of increasing weakness in early stages
  3. ) Immunosuppression with azathioprine (useful as steroid sparing)
  4. ) Thymectomy at ANY age increases chance of remission
  5. ) Plasmapheresis - intractable cases
34
Q

What antibiotics should be avoided in MG?

A

Certain antibiotics such as aminoglycosides can precipitate neuromuscular blockade especially if there are administered by rapid IV injection

35
Q

Differentials to consider in MG

A

Other causes of ptosis
Muscular dystrophies
Familial hypokalaemic paralysis

36
Q

What is the Eaton-Lambert myasthenic syndrome?

A

Paraneoplastic syndrome
Antibodies (usually against small cell carcinoma of the bronchus) block calcium channels in presynaptic terminals which inhibits ACh release

37
Q

How does Eaton-Lambert differ from MG?

A

In Eaton-Lambert the eyes are not usually as affected, proximal muscle weakness is common and strength is initially increased by repetitive movement

38
Q

Treatment for Eaton-Lambert

A

Diamondpyridine - blocks presynaptic potassium efflux thus potentiating Ca channel opening and ACh release

Year 4 - PAN (43 decks)

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