Dermatomyositis; inclusion body myositis Flashcards by patrick ellis

Describe the innervation of skeletal muscle [1]

Motor unit: formed of one motor neuron innervating mutliple muscle fibres

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Describe happens when muscle fibres become deinnervated [1]

All muscle fibres innervated by a damaged motor unit undergo atrophy

Damaged: arrow

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How does body adapt to damaged muscle fibres? [1]

Neighbouring muscle motor units can innervate damaged muscle fibres

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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

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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)

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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

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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

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Which fibres are affected first in motor neuron disease? [1]

Type 1 / slow fibres (with more mitochondria)

Type 1: darker

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Describe a myopathic reason for infantile hypotonia [1]

A few massive hypertrophic fibres alongside many very small fibres

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Describe a myopathic reason for infantile hypotonia [1]

A few massive hypertrophic fibres alongside many very small fibres

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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

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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

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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

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After taking a history, what would you do to assess muscle disorders? [2]

Biopsy
EMG

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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

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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.

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Whats the difference betwen polymyostis and dermatomyositis? [1]

Basically the same, but dermatomyositis patients also present with a rash

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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

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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

Which autoantibodies are present in polymyositis / dermatomyositis? [1]

What can be a trigger for this disease? [1]

Autoantibodies to anti nuclear antigens (ANA)
Associated with microbial infection

Describe the clinical features of polymyositis / dermatomyositis [2]

Symmetrical involvement of large proximal muscles of shoulders, arms and thighs
Serum creatine kinase raised - marker of disease

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

What is the outermost layer of skin called? [1]

**Stratum corneum**

Describe the change that occurs in subcutaneous calcifications [3]

Dermis-epidermal junction: **vacuoles develop, mucin deposite and calcifications**

Which antibody causes 20-40% liklihood of developing subcut. calcifications? [1]

**Anti-Jo1 antibody**

Describe treatment regime of dermatomyositis [4]

**Prednisilone** (type of corticosteroid): * 1 mg / kg per day until creatine kinase normal **Azthioprine** **Methotrexate** **Rituximab**

Describe the pathophysiology of inclusion body myositis [3]

Similar Alzeimers for your muscles: **amyloid; hyper-phosphorylated tau & APOE** in muscles

Which leg muscle is particularly affected in inclusion body myositis? [1]

**Quadriceps atrophy** **Wrist and finger flexor atrophy**

Describe the features of inclusion body myositis: - creatine kinase levels? [1] - Sex? [1] - Muscles affected? [2] - Which reflex is lost? [1]

* Mild **elevation** in **creatine kinase** * More common in **men** * Muscle weakness: **especially in finger and wrist flexors; knees extensors more than hip flexors** * **Quadricep reflex lost**

Which reflex is lost in body inclusion myositis? Bicep Tricep Quadricep Achilles

**Quadricep**

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**

Which muscular dystrophies are the most common? [2] Describe their inheritance [1]

**Duchenne & Becke Muscular Dystrophies**; **X-linked - recessive**

Describe pathophysiology of Duchenne MD [2] Which serum marker is raised in DMD? [1]

Healthy muscle: **dystrophin** is a ring around muscle fibre that connects the ECM to contractile apparatus so that endomesium moves with muscle Duchenne: **no muscle fibres with dystrophin**; causes elevated **creatine kinase**

Which muscle groups are most at risk in Duchenne MD? [2] What does this mean clinically? [2]

**Respiratory muscles & diaphragm**; die from resp. failure **Dilated cardiomyopathy occurs**; heart failure

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**

Treatment for DMD? [2]

**Prednisilone** Gene alterations

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

Which tissue is affected in fibromyalgia? [1] Which muscles are painful? [1] Which antibodies are present in 50% of patients? [1]

**Connective tissue damaged**; causes **widespread** **pain** in both sides and above & below waist axial skeleton pain **Antipolymer antibodies**

How do you diagnose fibromyalgia? [1]

Apply 2kg of pressure on 18 specific tender points in the body; **11/18 is a positive diagnosis**

Treatment options for fibromyalgia? [4]

**Amitriptyline** (TCA) **Fluxetine** (SSRI) **Exercise** **Complementary therapy**