Myopathies Flashcards
What are myopathies characterised by?
Prominent symmetrical proximal weakness and absent sensory changes
What are good questions to assess proximal weakness?
Legs: climbing stairs, stand from sit
Arms: reach above head, wash hair
What are the common medications causing neuropathy?
- Steroids
- Statins
- Anti-retrovirals
- Thyroxine
- Fibrates
- Cyclosporine
- Ipecac
Common drugs (i.e. non-prescription) causing myopathy?
- Ethanol
- Cocaine
- Heroin
What are the inherited myopathies?
DYSTROPHIES: -Myotonic dystrophy -Facio-scapulo-humeral dystrophy -Duchenne's dystrophy -Becker's dystrophy -Limb-Girdle dystrophies -PROMM METABOLIC: -McArdle's -CPT ION CHANNEL MUTATIONS: -Periodic paralyses (Hypo K+, Hyper K+, paramyotonia)
What are the acquired myopathies?
- DRUG: EtOH, statins
- ENDOCRINE/METABOLIC: hypothyroidism, hypokalemia
- INFLAMM: polymyositis, dermatomyositis, inclusion body myositis
Genetic mutation in myotonic dystrophy?
Unstable trinucleotide repeat in DMK gene (protein kinase) on Chr 19
Myotonic dystrophy inheritance pattern?
AD
Genetic mutation in Duchenne’s muscular dystrophy?
Loss of dystrophin gene on X chromosome
Ix in myopathy assessment?
- Electrophysiology (needle EMG)
- CK
- Genetic testing
- Muscle biopsy
Muscle biopsy features of muscular dystrophies?
- Varying muscle fibre size
- Regenerating and degenerating fibres
- Increased fibrosis
What are the special stains used to identify muscle membrane proteins in myopathy investigations?
- Dystrophin: Duchenne’s, Becker’s
- Dysferlin: limb girdle dystrophies
- Sarcoglycans: Limb girdle dystrophies
Pathophysiolgy of PM/DM?
Inflammatory cell infiltrate:
PM: CD8 mediated muscle necrosis found in adults
DM: B cell and CD4 immune complex mediated peri-fascicular vascular abnormalities
What is idiopathic inflammatory myopathy?
Autoimmune disease characterised by proximal muscle weakness +/- pain
Pathophysiology of inflammatory myopathy?
Muscle becomes damaged by a non-suppurative lymphocytic inflammatory process
How is idiopathic inflammatory myopathy characterised?
- Polymyositis and dermatomyositis
- Inclusion body myositis
Features of inclusion body myositis?
- Age >50y
- Slowly progressive
- Suspect when pt unresponsive to Rx
- Distal + proximal weakness
Biopsy features of inclusion body myositis?
- Vacuoles in cells on biopsy
- Biopsy positive for inclusion bodies
What are the criteria for PM/DM?
Probable if 3+, definite if 4+
- Symmetric proximal muscle weakness
- Elevated muscle enzymes
- EMG changes
- Muscle biopsy
- Typical rash of dermatomyositis
Typical site involvement in DM/PM?
Typical involvement of shoulder girdle and hip girdle
Which enzymes are elevated indicating PM/DM?
Increased CK, aldolase, LDH, AST, ALT
EMG changes of PM/DM?
Short polyphasic motor units, high frequency repetitive discharge, insertional irritability
Muscle biopsy features of PM/DM?
- Segmental fibre necrosis
- Basophilic regeneration
- Perivascular inflammation (DM)
- Enomysial inflammation (PM)
- Atrophy
Signs and symptoms of PM/DM?
- Progressive symmetrical proximal muscle weakness over w–> m
- Dermatological fx of DM
- CV: dysrhythmias, CHF, conduction defect, ventricular hypertrophy, pericarditis
- GIT: oropharyngeal and lower oesophageal dysphagia, reflux
- Pulmonary: weakness of resp muscles, ILD, aspiration pneumonia
