Disorders of muscle Flashcards
What are fasciculations?
Visible, fast, fine, spontaneous muscle twitches
What are some causes of fasciculations?
Physiological - Stress, caffeine, fatigue
Denervated muscle due to hyper excitability
Motor neurone disease
What is myotonia?
Failure of a muscle to relax after use
(Locking, sticking or cramping of the muscle)
What are some causes of myotonia?
Chloride and sodium channelopathies
What are some things examined for in muscle examination?
Inspection
Palpation
Strength testing
Fatiguability
How is muscle strength graded?
MRC muscle power grading:
- 0 – no movement at all
- 1 - flicker of movement when attempting to contract muscle
- 2 – some muscle movement if gravity removed but none against gravity
- 3 - movement against gravity but not against resistance
- 4 – movement against resistance but not full strength
- 5 – normal strength
What are some inflammatory myopathies?
Polymyositis
Dermatomyositis
Inclusion body myositis
What is polymyositis?
Idiopathic inflammatory myopathy that causes symmetrical, proximal muscle weakness
What is dermatomyositis?
Clinically similar to polymyositis but also has typical cutaneous manifestations
Describe the aetiology of polymyositis and dermatomyositis
- Idiopathic, autoimmune
- Higher prevalence in females (2:1)
- Peak incidence age 40-50
Describe the pathophysiology of dermatomyositis and polymyositis
- T cell mediated process against (unidentified) muscle antigens
- CD8+ T cells and macrophages surround, invade and destroy healthy, non-nectrotic muscle fibres
What are some symptoms of polymyositis?
- Symmetrical, proximal muscle weakness in the upper and lower extremities
- Insidious onset, worsening over months
- Often specific problems e.g. difficulty brushing hair, climbing stairs
- Myalgia in 25-50% (usually mild)
What are some signs of polymyositis?
- Muscle wasting
- Confrontational testing - direct testing of power
- Isotonic testing - 30 second sit to stand
What are some skin symptoms of dermatomyositis?
Gottron’s sign
Shawl sign
Heliotrope rash
What is shown?
Gottron’s sign
What is shown?
Shawl sign
What is shown?
Heliotrope rash
What are some lung symptoms of polymyositis?
- Interstitial lung disease (10% of patients, especially those positive for anti-Jo-1 antibody)
- Respiratory muscle weakness
What are some oesophageal symptoms of polymyositis?
Dysphagia (Poor prognostic sign)
What are some cardiac symptoms of polymyositis?
Myocarditis
What are some systemic features of polymyositis?
Fever
Weight loss
Raynaud’s phenomenon
Inflammatory arthritis
What are some investigations required in polymyositis
Bloods
Electromyography (EMG)
MRI
Muscle biopsy
What bloods are required in polymyositis?
CK
Inflammatory markers
Electrolytes, Calcium, PTH, TSH
Autoantibodies
What are some autoantibodies found in polymyositis?
Non-specific = ANA, anti-RNP
Specific = Anti-Jo-1, anti-SRP
What will show on MRI in polymyositis?
Show signal intensity abnormalities due to muscle inflammation, oedema, fibrosis and calcification
What will muscle biopsy show in polymyositis?
Perivascular inflammation and muscle necrosis
What is 1st line treatment of polymyositis?
Prednisolone (Reducing dose)
What are some 2nd line treatments of polymyositis?
- Immunosuppression - azathioprine/methotrexate/ciclosporin
- IV Ig
- Biological therapy e.g. rituximab (B cell depleting therapy)
What are some possible complications of polymyositis?
Increased risk of malignancy (Especially in males over 45)
What are some cancers that have an increased risk in polymyositis?
Ovarian, breast, stomach, lung bladder and colon cancers