Muscle and nerve disease Flashcards
(41 cards)
Describe excitation-contraction coupling.
It is a link between the AP generated in the sarcolemma and the start of a muscle contraction.
What is muscle?
An intricate machine designed to convert chemical energy to mechanical energy.
What are the common symptoms of muscle disease?
- weakness of skeletal muscle
- SOB (respiratory muscles)
- cardiomyopathy (Beckers MD starts with heart signs)
- poor feeding, failure to thrive and floppy (for children)
- cramp/pain
- myoglobulinuria (urine is black)
What are common signs of muscle disease?
- wasting/ hypertrophy/ pseudohypertrophy (muscle is replaced by fibrous tissue)
- normal/ reduced tone and reflexes
- motor weakness (NOT SENSORY)
What are the common investigations of muscle disease?
- history and examination
- CK (creatinine kinase - levels will be higher if muscle is being broken down)
- EMG (electromyogram - records the electrical impulses in muscle)
- muscle biopsy
- genetic testing
What are the classifications of muscle diseases?
- muscular dystrophies
- channelopathies
- metabolic muscle disease
- inflammatory muscle disease
- congenital myopathies
(all except inflammatory muscle disease are single gene defects)
What is abnormal in the muscular dystrophies?
Functional dystrophin and actin are needed for the contractile mechanism within the cell. Lots of different proteins work in sync to make this happen. In MD, dystrophin doesn’t work properly.
Give examples of muscular dystrophies.
- Duchenne’s MD (dystrophin is completely abnormal)
- Beckers MD (dystrophin is mildly abnormal)
- Myotonic dystrophy (most common form)
- Facioscapulohumeral MD
- Limb-girdle MD
Which genetic phenomenon is seen with myotonic dystrophy?
Anticipation - caused by triplet repeats and so symptoms become more and more apparent as more repeats are added on in each generation, so gets more severe.
What are the channelopathies?
Disorders of Na, Ca and Cl channels.
Give some examples of channelopathies.
- familial hypokalemic periodic paralysis: problem with contraction
- hyperkalaemia periodic paralysis: problem with contraction
- paramyotonia congenita: problem with relaxation
- myotonia congenita: problem with relaxation
What is metabolic muscle disease?
Disorders of carbohydrate or lipid metabolism. Also mitochondrial myopathies/cytopathies.
Give examples of metabolic muscle diseases.
Disorders of carbohydrate metabolism:
- McArdle’s: person finds it hard to exercise for the first min and so needs to consume sugar, then lipid metabolism takes over
- hard to get going
Disorders of lipid metabolism:
- during exercise they are fine for the 1st 10 mins as they are using carbohydrate metabolism, then they need to stop
- can only exercise in short bursts
Give 2 examples of inflammatory muscle diseases.
- polymyositis
- dermomyositis
What are the symptoms of inflammatory muscle disease?
- painful, weak muscles
- dermomyositis has a characteristic rash (heliptropic - eyes, fingers and elbows)
- any age
How are inflammatory muscle diseases investigated and treated?
Investigation:
- CK
- EMG
- biopsy (PM CD8 cells and DM Bcl/CD4 as humoral)
Treat with immunosuppression.
What is the normal process occurring at the NMJ?
- nerve releases ACh
- ACh binds to the AChR
- muscle contracts
- ACh broken down by acetylcholinesterase
Name 1 disorder of the NMJ.
Myesthenia Gravis.
What is the clinical presentation of MG?
FATIGUABLE WEAKNESS:
- limbs
- eyelids (ptosis)
- talking
- SOB
- diplopia
What causes MG?
Auto-antibodies block the AChR. When ACh comes along there’s not as many receptors for it to bind to as auto-antibodies are taking them all up.
What are the investigations for MG?
- AChR Ab (70% positive)
- Anti-MuSK Ab (30% positive)
- Neurophysiology (repetitive stimulation of the nerve will cause decrement)
- CT chest (as differential is malignant thymoma)
Diagnostic:
- Tensilon test: inject tensilon which blocks the anti-ACh Ab’s
How is MG treated?
Symptomatic:
- acetylcholinesterase inhibitor: prevents ACh breakdown so gives ACh time to find an AChR that hasn’t been taken upby autoantibodies
Immunosuppression:
- prednisolone and a steroid-saving agent like azathioprine so that less steroid can be used
–> use both
Why may MG present in the old and young?
Young: thymic hyperplasia
Old: malignant thymoma
–> thymectomy in females < 40 with malignant thymoma
What do peripheral nerves consist of?
- sensory axons: small fibres for pain and temp, large fibres for vibration sense and proprioception
- motor axons
- ANS
