Pathology of the Musculoskeletal System 2 - Muscles PDF

Preview

Summary

Rute...

Description

Pathology of the Musculoskeletal System 2 - Muscles Explain the sequence of events in Myofiber necrosis and healing Response to Insult - Fibre swelling, eosinophilia, loss of striation - Fragmentation - coagulative necrosis + calcification - Macrophages - Satellite Cell (stem cell) Hypertrophy + Migration - Satellite Cell differentiation → Myoblasts → Fusion → Myotubes - Reformation of Plasmalemma - Nuclei return to periphery - Cross-striations reappear Large defect → Filled with Fibre = Scar Plasmalemma damage → Leak of enzymes (CK and AST) Myofiber Degeneration - Single Injury → Focal Monophasic Degeneration - Single Insult (Toxin, Chemical, Metabolic event) → Multifocal Monophasic Degeneration - Repeated Injury (same site) → Focal Polyphasic Degeneration - Repeated Insult (Toxin, Nutritional, Genetic) → Multifocal Polyphasic Degeneration Differentiate between various causes of skeletal muscle atrophy Adaptation - Atrophy - Denervation → no contraction stimulus - Rapid atrophy all of innervated myofibers - Myofibers shrink → Nuclei left - Patchy or Diffuse - depends on compensation by other nerves - Disuse - e.g. E.g. Lameness, immobilisation, recumbency - Muscle not exposed to repeated tension - Rapid decrease in size - Reversible - Metabolic Muscle Atrophy - Malnutrition, Cachexia, Senility - Wasting dz - e.g. parasitism, neoplasia - Catabolism of muscle - reserving nutrients for vitals - Neoplasia - Circulating cytokines (e.g. TNF-a) - Consume nutrients or muscle directly - Chronic inflammatory environment → increased energy demand

-

-

Endocrinopathies - Direct/Indirect - Hyperadrenocorticism - Hypothyroidism - Generalised Muscle Atrophy → Weakness, distended abdomen, megaoesophagus Hypertrophy - Increased demand - Ddx = Lipomatous pseudohypertrophy (bovine) - Increased muscle mass but replacement is with Adipose - Genetic

List examples and compare between degenerative, inflammatory, congenital, endocrine and metabolic myopathies List some causes of paralysis Congenital - e.g. X-Linked Muscle Dystrophy - Golden and Labrador Retrievers - Female Carrier → Compensation by healthy X - Males → CS = Stiff, Exercise intolerance, Difficulty swallowing - Lack of Dystrophin → Repeated episodes of Myonecrosis → Fibrosis - Affects cardiac muscles → HF - Dx = Increased CK, AST Vascular Disorders = Ischaemia - Vessel Occlusion - Capillary anastomoses + contralateral circulation = compensatory - Causes - Thromboembolism (Iliac trifurcation in cats) - Vasculitis - Heartworm - Compression - E.g. Downer cow, Post anaesthetic myopathy (horses) - External pressure on capillaries > perfusion pressure - Compartment Syndrome - Swelling of vigorously exercised muscle in non-expandable compartment (fascia or bone) - Increased intramuscular pressure → vascular occlusion - E.g. Green Muscle Dz (turkeys, chickens) - Supracoroid muscles Nutritional - Deficiency of Selenium +/- Vitamin E - White Muscle Disease - Herbivores (esp. young) - CS = Weak, Stiff gait, Suckling problems, Dysphagia - Gross = Bilaterally symmetrical pallor

Toxic -

Microscopic = Multifocal Polyphasic. Basal lamina intact → regeneration possible

E.g. Botulism (flaccid paralysis) - Clostridium Botulinum exotoxin - Horses and Birds - Routes - Ingestion of preformed toxin in feed - Growth of spores within GIT (shaker foals) - Wound infection - Toxin enters bloodstream → targets nervous system → Prevents ACh release from presynaptic vesicles - Fatal - E.g. Tetanus (spastic paralysis) - Clostridium tetani → Tetanospasmin - Horses - Spore growth in anaerobic wound → Tetanospasmin enters bloodstream → targets nervous system → No release of inhibitory neurotransmitter (Glycine + GABA) Inflammation - Bacterial Myositisides - Portals - Direct - e.g. FB - Haematogenous - Extension or local infection - Suppurative = Pyogenic Bacteria (e.g. Strep equi, Corynebacterium pseudotuberculosis, Trueperella pyogenes, Pasteurella multocida) - (Sero)Haemorrhagic = Toxins - Blackleg (Clostridium chauvoei) - Beef cattle - Malignant Oedema (Clostridium septicum) - Gaseous Gangrene - Clostridium perfringens Type A - Clostridium novyi Type A → Big Head in Rams - Granulomatous - Actinomyces bovis → Lumpy Jaw - Actinobacillus lignieresii → Wooden Tongue - Viral Myositisides - Vasculitis → Infarction - e.g. Bluetongue - Direct Multifocal necrosis - e.g. Enteroviruses, FMD - Parasitic - Immune Mediated - E.g. Masticatory Muscle Myositis - GSD - Circulating Abs to Type 2M Myosin (unique to masticatory muscles)

-

Acute = Swelling + Pain Chronic = Muscle atrophy Histopathology = Eosinophils, Plasma cells, Lymphocytes, Macrophages, Fibrosis

Neoplasia - Uncommon - Rhabdomyomas = Benign - Dog → Larynx - Cattle/Pigs → Heart - Rhabdomyosarcoma = Malignant - Younger animals? - Locally invasive, rapid growth, central necrosis - Associated tissues - e.g. Fibrosarcoma (cat), Haemangiosarcoma, Infiltrative Lipoma - Metastatic - e.g. Lymphoma, Melanoma...