Dermatomyositis; inclusion body myositis Flashcards
Describe the innervation of skeletal muscle [1]
Motor unit: formed of one motor neuron innervating mutliple muscle fibres
Describe happens when muscle fibres become deinnervated [1]
All muscle fibres innervated by a damaged motor unit undergo atrophy
Damaged: arrow
How does body adapt to damaged muscle fibres? [1]
Neighbouring muscle motor units can innervate damaged muscle fibres
Describe what a target fibre is [1]
Why does a target fibre arise? [1]
Describe the apperance [1]
When a damaged muscle is re-innervated; nuclei of muscle moves centrally and causes the production of new actin and myosin fibres
Occurs due to satellite cells differentiating and proliferating
Describe a scenario when a fast muscle fibre become a slow muscle fibre? [1]
How does this appear histologically? [1]
Re-innervation of muscle fibre occurs: fast muscle fibre is re-innervated by a slow muscle fibre
Causes a grouping of fast and slow muscle fibres (usually they’re seperate)
Describe the effect of fibres becoming grouped due to re-innervation on motor neurons [2]
Puts stress onto the remaining motor neurons that are left
If motor neurons die: group atrophy occurs
Which are the slow & fast fibres in this stain? [2]
Slow fibres (Type 1): more mitochondria - darker stain
Fast fibres (Type 2): less mitochondria - light stain
Which fibres are affected first in motor neuron disease? [1]
Type 1 / slow fibres (with more mitochondria)
Type 1: darker
Describe a myopathic reason for infantile hypotonia [1]
A few massive hypertrophic fibres alongside many very small fibres
Describe a myopathic reason for infantile hypotonia [1]
A few massive hypertrophic fibres alongside many very small fibres
Describe the two types of infantile myopathic hypotonia from congenital fibre type disproportion [2]
Congenital fibre type disproportion:
* Large type 1 muscle fibres
* Small type 2 muscle fibres
OR
* Small type 1 muscle fibres
* Large type 2 muscle fibres
Describe the effects of infantile myopathic hypotonia by the time the children have grown to 2 [2]
By the age of 2:
* hypotonia has mostly dissapeared
* have reduced exercise resilience
Describe the pathophysiology of sarcopenia
- 0.5 - 1% of muscle mass is lost each year after age of 50; 3-5% if inactive
- Muscle replaced with fat
- No difference in men and women
- Causes an increase likelihood of fractures
- Impaired balance
After taking a history, what would you do to assess muscle disorders? [2]
Biopsy
EMG
Which muscle fibres degenerate more in sarcopenia? [1]
Generally, a significant decline of type II, but not type I muscle fibers are observed in sarcopenic patients
How does an EMG present with patients who have myopathy?
Compared to healthy and neuropathy patients [2]
In myopathic motor units, the number of functional muscle fibers is reduced. Therefore motor unit action potentials (MUAPs) are smaller in amplitude and duration. Because of the asynchronous firing of affected muscle fibers, the morphology of MUAPs become polyphasic.
Whats the difference betwen polymyostis and dermatomyositis? [1]
Basically the same, but dermatomyositis patients also present with a rash
How does a patient with dermatoymositis present? [4]
Rash around eyes
Peri-orbital oedema
V sign of neck due to increased photosynsetivity
Gottron’s sign
How does a biospy from a patient with polymyositis / dermatomyositis present? [1]
- (some have subclinical muscle involvement)
- Muscle generally not involved; CD8 T cells cells infiltrate the periphery of the muscle fasicle
- Central nuclei
- Variation in fibre size
Describe the effect of CD8 infiltration in dermatomyositis [1]
CD8 T cells bind to MHC 1 to create: CD8-MHC1 complex
How do skin lesions differ between caucasian and black patients? [1]
Caucasian: Purple in colour; peri orbital oedema: aka Heliotrope rash
Black: paler red rash
How do skin lesions differ between caucasian and black patients? [1]
Caucasian: Purple in colour; peri orbital oedema: aka Heliotrope rash
Black: paler red rash
Which leg muscle is particularly affected in inclusion body myositis? [1]
Quadriceps atrophy
Wrist and finger flexor atrophy
Describe histology of body inclusion myositis [2]
Muscle fibres contain empty vacuoles and clumps of empty material that contain amyloid like material
What histological staining can you conduct for body inclusion myositis? [1]
Congo red: amyloid goes red
How does early DMD appear histologically? [3]
Fibre size variation
endomysial & perimysium fibrosis
Degenerating muscle fibres undergoing myophagocytosis
How does late DMD appear histologically? [2]
Loss of muscle; atrophy of fibres and death - replaced with fibrotic material and fat
How do statins affect 10% muscle? [2]
Rhabdomyolysis; get vacuoles in type 2 muscle fibres
Name and describe how two therapeutic drugs cause myopathy [2]
Corticosteroids; cause dose dependent type 2 atrophy
Hydroxychloroquine: not dose dependent atrophy; lysosomes damaged
Hydroxychloroquine causing lysosome damage
