Muscle disorders

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Information about Muscle disorders

Published on October 28, 2018

Author: drpriya07


1. Muscle disorders Dr Anu Priya J

2. Muscle disorders  Diseases affecting neuromuscular junction • Myasthenia gravis • Lambert-Eaton syndrome  Effects of denervation of muscle • Fibrillation • Fasciculation • Muscle atrophy • Denervation hypersensitivity  Muscle dystrophies  Muscle hypertrophy  Metabolic myopathies  Muscle paralysis

3. Myasthenia gravis • Myo=muscle; asthenia=weakness; gravis= serious Pathogenesis • Autoimmune disease • Formation of circulating antibodies which destroy the nicotinic Ach(acetylcholine) receptors on the postsynaptic membrane of neuromuscular junction Clinical features • Skeletal muscles are weak & fatigued • Rare, serious & sometimes fatal

4. Myasthenia gravis Investigations • Radioimmunoassay – Ach receptor antibodies detected in 90% of patients • Histology – decreased number of subneural clefts, widening of the synaptic cleft, hyperplasia of thymus gland.

5. Myasthenia gravis Treatment • Neostigmine – drug of choice – reversible AchE inhibitor • Immunosuppression – suppress antibody production – steroid - high dose of cortisol • Thymectomy – as excessive synthesis of thymic hormone is one of the contributing factors • Plasmapheresis

6. Lambert-Eaton syndrome • Autoimmune disease • Autoantibodies against one of the voltage gated calcium channels in the nerve ending at neuromuscular junction • Decreased calcium influx at the synaptic knob that causes Ach release, leading to decreased acetylcholine release • Muscle weakness

7. Fibrillation • In the intact body, skeletal muscle contracts only if its motor nerve supply is stimulated • Destruction of this nerve supply leads to abnormal excitability of the muscle & fine, irregular contractions of the individual fibres called fibrillation

8. Fibrillation • Fibrillation is seen for several weeks after injury, and then ceases as the muscle cells atrophy. • Fibrillation also ceases if the motor nerve regenerates.

9. Fibrillation • Due to denervation hypersensitivity • Classical picture of LMN lesion • Such contractions are not visible grossly, but fibrillation potentials can be recorded by EMG using needle electrodes.

10. Fasciculations • Jerky, visible contractions (twitching) of groups of muscle fibres • As a result of pathological, spontaneous discharge of spinal motor neurons • Seen in diseases affecting the anterior horn cells • Example : Poliomyelitis

11. Muscle atrophy • Atrophy/ Muscle wasting • When there is permanent loss of nerve supply to a muscle, the muscle shows flaccid paralysis & atrophy.

12. Muscular dystrophy • Term used to denote a group of degenerative diseases that cause progressive weakness of skeletal muscle. • Mild or severe or fatal depending on the type of muscular dystrophy • Causes – depends on the type of muscular dystrophy; mostly genetic - mostly mutations in the genes coding for the various components of the dystrophin- glycoprotein complex. • Dystrophin gene is one of the largest in the body, & mutations can occur at many different sites in it.

13. Muscular dystrophy Duchenne muscular dystrophy • X linked recessive disease; males affected • Mutation in the gene coding for dystrophin- glycoprotein complex • Serious form of muscular dystrophy; usually fatal by the age of 30 • Dystrophin protein is absent from the muscle

14. Muscular dystrophy Duchenne muscular dystrophy • Typical feature – the child uses his hands to climb up, while getting up from the floor. • Wheelchair by age 12 • Fatal by age 30

15. Muscular dystrophy Duchenne muscular dystrophy • Progressive muscle weakness, that becomes apparent by age 4 • Muscle hypertrophy especially calf & pelvifemoral muscles • Cardiomegaly

16. Muscular dystrophy Duchenne muscular dystrophy • Enlargement occurs due to gradual degeneration & necrosis of muscle fibers that are replaced by more fibrous & fatty tissue.

17. Muscular dystrophy Becker muscular dystrophy • X linked genetic disease • Mutation in the gene coding for dystrophin- glycoprotein complex • Milder form of muscular dystrophy; not very fatal • Dystrophin protein is present in the muscle but altered or reduced in amount

18. Muscular dystrophy Other muscular dystrophies • Mutations in the gene coding for titin, desmin, sarcoglycans & other components of the dystrophin-glycoprotein complex, etc.,

19. Normal protein

20. Mutation

21. Breakage in cell membrane following muscle contractions

22. Entry/leakage of calcium from ECF to ICF

23. Calcium activates proteases that breakdown proteins in the muscle

24. Action of proteases in normal levels

25. When protease conc inc

26. Leakage of CK – inc CK

27. Males affected

28. Metabolic myopathies • Mutations in genes that code for enzymes involved in the metabolism of carbohydrates, fats, and proteins to CO2 and H2O in the muscle and production of ATP • Exercise intolerance and possibility of muscle breakdown due to accumulation of toxic metabolites • Ex: McArdle’s disease

29. Muscle channelopathies • Calcium release channels – RYR – malignant hyperthermia

30. Muscle sprain • Due to overstretching or forced extension of an active muscle. • Often during sports activity or physical labor • Injury at the myotendinous junction or separation of the fibers • Pain, soreness, weakness & swelling • Treat – ice packs, rest, immobility • Drugs for pain relief • Surgery – if required, to correct the damage

31. Muscle cramp • Generation of nerve action potential at a very high rate • Painful condition • Involuntary tetanic contraction of the skeletal muscle • Mechanism: Electrolyte imbalances in the ECF surrounding both the muscle and nerve fibers • Excessive exercise or persistent dehydration • Other causes of electrolyte disturbances

32. EMG • The process of recording the electrical activity of muscle • Electromyography • Surface or needle electrodes • Study the activation of motor units Uses: • Diagnosis of certain muscle disorders. Example: Fibrillation potentials – can be recorded using EMG; not visible grossly over the muscle. • Research

33. Thank you

34. Denervation hypersensitivity • Seen following nerve injury • Increased number and sensitivity of receptors in the postsynaptic membrane following denervation • The muscle becomes hypersensitive to the neurotransmitter substance that is released by its nerve terminals

35. • Muscle rigor gan ebk pg 122 • Myotonia

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