Muscle and Nerve disease Flashcards
What neurotransmitter is released at the neuromuscular junction?
Acetyl-choline (ACh)
Binds to the ACh receptor
What are the typical symptoms for a patient with muscle disease?
Symptoms:
- SOB/Dyspnoea - due to weakness of respiratory muscles
- Dysphagia/Aspiration - weakness of bulbar muscles
- Cardiomyopathy
- Cramp, pain, stiffness
- Myoglobulinuria
What typical signs are present with muscle disease?
- Wasting / Hypertrophy:
- Inspection of patient
- Normal or reduced tone and reflexes
- Motor weakness - but not Sensory weakness:
- Tests such as pinprick test will be normal
- Tests of power etc will show weakness
How would you investigate a patient with possible muscle disease?
History and Examination
Creatine Kinase (CK) - marker of muscle breakdown & damage. Also used for MI, acute Kidney injuries etc
EMG - Electromyography
Muscle biopsy
Genetic testing
Why is Electromyography a useful investigation for Muscle disease?
Effective at evaluating and recording the electrical activity produced by skeletal muscles
Will measure the action potentials produced by motor neurones
What information is gained from taking a muscle biopsy?
Structure
Biochemistry
Inflammation
What aspects of muscle function can be affected in congenital/genetic muscle diseases?
Structural - Muscular dystrophies
Contractile - Congenital myopathies
Coupling - Channelopathies
Energy - Abnormalities of enzymes/mitochondria
What are the 4 main categories of acquired muscle diseases?
Metabolic - Involving Ca2+, K+
Endocrine - Thyroid, adrenal, Vitamin D
Inflammatory muscle disease
Iatrogenic - from medications such as steroids, statins
What are muscular dystrophies?
A group of Inherited muscle diseases in which there is increasing weakening and breakdown of skeletal muscles over time
There is no cure for MD thus treatment is therapy is generally aimed at improving quality of life
In muscular dystrophies - what causes the muscles to weaken and atrophy?
Normally - the dystrophin protein links intracellular actin to the DAP complex in the cell membrane. The DAP is in turn linked to the extracellular matrix. This is to stabilize the sarcolemma.
In MD - no/abnormal dystrophin protein - no support - everything wilts and sarcolemma breaks. This allows Creatine Kinase to escape from the cell and Ca2+ entry to cells
Contrast the short-term and long-term effects on the muscle in muscular dystrophies such as DMD
In the short term:
- Muscle regeneration takes place to try and combat the cell death
- This leads to Some fibres becoming very large compared to others - giving a varied size of muscle fibres
In the Long term:
- Muscle atrophies
- Infiltration of fat and fibrotic tissue
Identify the labels in this diagram of the dystrophin-associated protein complex and all that stuff
What patients are most likely to have muscular dystrophies?
Younger or older onset
More common in males (although depends on specific type of MD)
What are the main types of Muscular dystrophy?
Dystrophinopathies - mutation of dystrophin gene:
- Duchenne’s (DMD) - most common
- Becker’s (BMD)
Other:
- Facioscapulohumeral MD
- Oculopharyngeal MD
- Limb girdle MD
- Myotonic dystrophy (cataracts)
What presentation is typical to:
A) Facioscapulahumeral MD
B) Oculopharyngeal MD
C) Limb-girdle MD
A) Develops at young age - weakness in skeletal muscles of face, scapula and upper arms
B) Adult onset - Weakness of upper eyelids & throat. Presents with ptosis & dysphagia
C) Any age - Weakness of skeletal muscles of arms & legs
What are channelopathies and how do they present?
Disorders of Ca2+, Na+, K+ & Cl- channels
Often paroxysmal symptoms - eg periodic paralysis / myotonia (delayed relaxation after contraction)
Partially treatable
Describe what a metabolic myopathy is
Disorders corresponding to energy production - characterized by mitochondrial problems
Exercise-induced:
- Early = disorders of carbohydrate metabolism
- Late = disorders of lipid metabolism
Partially treatable
What are the 2 main types of inflammatory myopathies (myositis) and their basic differences?
Polymyositis & Dermatomyositis (DM)
Polymyositis causes muscle weakness, usually in the muscles closest to the trunk of your body. Dermatomyositis causes muscle weakness, plus a characteristic skin rash.
In essence: Dermatomyositis = Polymyositis (muscle involvement) + skin involvement
