Pathology of the Musculoskeletal System 2019-2020 PDF

1. Pathology of the Musculoskeletal system Systemic Pathology 2019-2020 Higher Colleges of technology INTRODUCTION: SKELETAL MUSCLE STRUCTURE Skeletal muscle - Elongated myofiber cells - Multinucleated cells (100-300) - Nucle...

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Pathology of the Musculoskeletal system Systemic Pathology 2019-2020 Higher Colleges of technology INTRODUCTION: SKELETAL MUSCLE STRUCTURE Skeletal muscle - Elongated myofiber cells - Multinucleated cells (100-300) - Nucleus remains peripheric - Non Branched, parallel arrangement - Connective tissue between - Sarcoplasm with a lot of myofibrils (striation pattern) INTRODUCTION: SKELETAL MUSCLE STRUCTURE Skeletal muscle - Nucleus remain peripheric - Each fiber is surrounded by a fine layer: Endomysium - Groups of fibers are surrounded by another layer: Perimysium - Spaces observed between fibers: Interstitium Perimysium Endomysium Nucleus Skeletal striated Cell INTRODUCTION: SKELETAL MUSCLE STRUCTURE Bone Perimysium Blood vessel Muscle Fiber Fascicle Tendon Epimysium Endomysium Muscle Epimysium Fiber Perimysium Muscle Fascicle Endomysium INTRODUCTION: SKELETAL MUSCLE STRUCTURE Skeletal muscle - Sarcomere: Basic anatomic and functional unit of the muscle INTRODUCTION: SKELETAL MUSCLE STRUCTURE Sarcomere Line Z Line Z INTRODUCTION: SKELETAL MUSCLE STRUCTURE Skeletal muscle motor unit INTRODUCTION: SKELETAL MUSCLE STRUCTURE Skeletal muscle fibers according to their metabolism, and contracting capacities Two types - Type I: Red (myoglobin), Slow twitch and slow fatiguing. Energy comes from oxidative metabolism. Many mytochondria - Type II: White, Fast twitch and fast fatigue. Energy comes from glycolysis. Two subtypes INTRODUCTION: SKELETAL MUSCLE STRUCTURE Type I fibers - Dark muscles (i.e. diaphragm and intercostal muscles) Type II fibers - Pale muscles (i.e. gluteal muscles) Histochemistry necessary to differentiate them. INTRODUCTION: SKELETAL MUSCLE STRUCTURE Muscle fibers - Pectoral muscles of chickens are rich in type II fibers contrary to their legs. - Long distance flying birds have pectoral muscles rich in type I fibers. Very efficient oxygen metabolism. - Distribution of fibers will affect the presence of one or other diseases. INTRODUCTION: SKELETAL MUSCLE FUNCTIONS Skeletal muscle functions - Posture and enabling movement for locomotion. - Precise movements (i.e. eyes) - Joint stability - Proprioception - Body protection - Stimulus for the blood vessels (Blood pumping against gravity) - Body homeostasis: Heat production  MUSCULOSKELETAL EXAMINATION Skeletal muscle examination - Color - Volume - Compare to the opposite side if bilateral - Texture - Appearance - Answer to stimulus - Histopathology  SKELETAL MUSCLE DISEASE Skeletal muscle Disease - Directly related to the peripheral nervous system - Muscle function/activity determined by the motor neuron responsible for its innervation - Two types of possible changes - Neuropathic: Failure in nerve signal transmission - Myopathic: Failure in the muscle cell metabolism or functions  SKELETAL MUSCLE DISEASE Possible Clinical signs - Atrophy - Hypertrophy - Swelling - Weakness - Pain - Muscle spasm - Abnormal gait  SKELETAL MUSCLE DISEASE Disease portal entries for skeletal muscle disease - Wounds - Intramuscular injections - Bone fracture creating trauma - External pressure - Blood pathogens, toxins, autoantibodies… - Inflammatory cells  SKELETAL MUSCLE DISEASE Skeletal muscle Disease - Directly related to the peripheral nervous system - Muscle function/activity determined by the motor neuron responsible for its innervation - Two types of possible changes - Neuropathic: Failure in nerve signal transmission - Myopathic: Failure in the muscle cell metabolism or functions  SKELETAL MUSCLE DISEASE A. Developmental abnormalities B- Degenerative alterations: Atrophy (3 types) - Denervation atrophy - Disuse atrophy - Malnutrition atrophy Hypertrophy Muscle degeneration and necrosis Calcification C- Muscle repair: Regeneration D- Myopathies E- Myositis  SKELETAL MUSCLE DISEASE A. Abnormalities of growth and development Arthrogryposis - Congenital in fetuses and stillborns. - Small limbs with rigid joints - Rigidity comes from muscular hypoplasia> lack of innervation during pregnancy. - Frequently seen in pathologies related to brain or spinal cord gestation alterations - Cause may be ingestion of toxicants (mother), viral infection (BVD) - Usually Dystocia due to the joint rigidity  SKELETAL MUSCLE DISEASE Abnormalities of growth and development Arthrogryposis  SKELETAL MUSCLE DISEASE A. Abnormalities of growth and development Myofibers Hypoplasia - Hind limbs affected - No muscular lesion - Less myofibers than expected (in number and diameter) - Flask limbs with lack of innervation as well. - Not to confuse with athrophy  SKELETAL MUSCLE DISEASE A. Developmental abnormalities B- Degenerative alterations: Atrophy (3 types) - Denervation atrophy - Disuse atrophy - Malnutrition atrophy Hypertrophy Muscle degeneration and necrosis Calcification C- Muscle repair: Regeneration D- Myopathies E- Myositis  SKELETAL MUSCLE DISEASE B. Degenerative Alterations I. Atrophy (3 types) i. Denervation atrophy - Lack of tonic stimuli - Localized loss of nerve function or loss of the entire motor unit. - 50% of the mass can be lost very quickly (few weeks) - Radial nerve damage due to trauma (camels, dogs) - Laryngeal hemiplegia (Left recurrent laryngeal nerve) - Usually not bilateral  SKELETAL MUSCLE DISEASE Degenerative alterations I. Atrophy (3 types) ii. Disuse atrophy - Intact innervation - Reduced movement because of pain - Typical from fracture, ankylosis, tenotomy. - Localized lesions to the affected structures  SKELETAL MUSCLE DISEASE Degenerative alterations I. Atrophy (3 types) ii. Malnutrition atrophy - Emaciation, cancer and chronic inflammatory disease - Muscle becomes the source of nutriments (proteins) - Starts after finishing the fat reserves - IL1 (cancer and chronic diseases) associated as cachected. - Nerve stimulus remains intact. - Generalized.  SKELETAL MUSCLE DISEASE A. Developmental abnormalities B- Degenerative alterations: Atrophy (3 types) - Denervation atrophy - Disuse atrophy - Malnutrition atrophy Hypertrophy Muscle degeneration and necrosis Calcification C- Muscle repair: Regeneration D- Myopathies E- Myositis  SKELETAL MUSCLE DISEASE Degenerative alterations II. Hypertrophy - Response to an increase in work demand - Genetic selection - Increase of size but not number - Formation of new myofilaments - Associated to steroidal drugs as well  SKELETAL MUSCLE DISEASE A. Developmental abnormalities B- Degenerative alterations: Atrophy (3 types) - Denervation atrophy - Disuse atrophy - Malnutrition atrophy Hypertrophy Muscle degeneration and necrosis Calcification C- Muscle repair: Regeneration D- Myopathies E- Myositis  SKELETAL MUSCLE DISEASE Degenerative alterations III. Muscle degeneration and necrosis - Sequel to myofiber injury - Can be reversible to a point of no return: Necrosis - Only detected in grossly severe lesions - Degenerated muscles appear pale (not confuse with anemia, fat or exsanguination) - Microscope: Loss of striations, rupture of fibers. Calcification - A: Normal Myofiber - B: Coagulation necrosis - C: Disolution of the necrotic segment (Macrophages) - D: Migration of satellite cells to the center - E: Formation of myoblasts - F: Regenerating myofiber SKELETAL MUSCLE DISEASE SKELETAL MUSCLE DISEASE SKELETAL MUSCLE DISEASE  SKELETAL MUSCLE DISEASE Degenerative alterations Muscle degeneration and necrosis - If there is release of myoglobin or haemorrhage> Darker - Animals prostrated several days> Ischemia> Necrosis - Cumulation of blood in the recumbent area - Called red imbibition.  SKELETAL MUSCLE DISEASE Degenerative alterations IV. Calcification - Deposition of Ca++ - Common to muscle degeneration and necrosis - Calcified fibers look granular and bluish granules resembling bacteria - Special stain  SKELETAL MUSCLE DISEASE A. Developmental abnormalities B- Degenerative alterations: Atrophy (3 types) - Denervation atrophy - Disuse atrophy - Malnutrition atrophy Hypertrophy Muscle degeneration and necrosis Calcification C- Muscle repair: Regeneration D- Myopathies E- Myositis  SKELETAL MUSCLE DISEASE C. Muscle repair Regeneration - Great regenerative capacity - 1. Macrophages clean the cell debrids within - 2. Sarcolemmal tubes (Endoysium+ basal lamina)> Scaffold for the myoblasts. They prevent fibroblasts to mix with them. - 3. Myoblasts undergo mitosis>creation of new sarcomeres - 4. If sarcolemmal tubes broken: Scar  SKELETAL MUSCLE DISEASE A. Developmental abnormalities B- Degenerative alterations: Atrophy (3 types) - Denervation atrophy - Disuse atrophy - Malnutrition atrophy Hypertrophy Muscle degeneration and necrosis Calcification C- Muscle repair: Regeneration D- Myopathies E- Myositis  SKELETAL MUSCLE DISEASE D. MYOPATHIES I. Nutritional - White muscle disease ( Nutritional myodegeneration) II. Metabolic - Porcine stress syndrome III. Exertional - Azoturia - Capture myopathy - Tying up - Compartment syndrome IV. Traumatic - Downer cow syndrome - Crush syndrome - Post-anesthetic  SKELETAL MUSCLE DISEASE I. NUTRITIONAL MYOPATHIES White muscle disease - Very common in farm animals - 50% mortality - Affects growing animals (less common in foals and goates - Associated to vit E/Se deficiency - Worsened by the environment and exercise - Nutrition and some toxics  SKELETAL MUSCLE DISEASE NUTRITIONAL MYOPATHIES White muscle disease - Occasionally in neonates - Related to the oxidation of cell membrane lipids Lack of Vitamin E + Se Lipoperoxidation by free radicals (Oxygenation/antioxidant) Influx of Ca ++ into the sarcoplasm and mitochondria Energy (Calcium removal) Exhaustion of the cell Degeneration of myofibers Necrosis  SKELETAL MUSCLE DISEASE NUTRITIONAL MYOPATHIES White muscle disease  SKELETAL MUSCLE DISEASE NUTRITIONAL MYOPATHIES White muscle disease histopathology  SKELETAL MUSCLE DISEASE II. METABOLIC MYOPATHY Porcine stress syndrome or Porcine Malignant Hyperthermia - Very important meat industry in Europe - Respiratory and metabolic acidosis - Myoglobinemia, Hyperkalemia, High blood lactate, Hyperthermia, cardiovascular collapse>Death - Inherited defect in storage and release of Ca++ - Denaturation of sarcoplasmic proteins - Muscles look pale and wet.  SKELETAL MUSCLE DISEASE III. EXERTIONAL MYOPATHIES - Group of muscular diseases after stenous exercise - Similar to WMD but affect major muscle masses (Type II fibers) - Rapid utilization of glycogen> Cummulation of lactic acid - Protein structure alteration - Loss of water - Interstitial Edema, Ischemia, degeneration, necrosis - Myoglobinemia, myoglobinuria i. Azoturia ii. Capture myopathy iii. Tying up iv. Compartment syndrome  SKELETAL MUSCLE DISEASE III. EXERTIONAL MYOPATHIES Azoturia (Monday morning disease, sacral paralysis, Tying Up) - Before it was thought related to a rich carbohydrates diet. - Now: Polysaccharide storage myopathy (PSSM). - Signs: - Muscle weakness - reluctance to move - Recumbence - diaphoresis, - Myoglobinuria - Renal failure - Acidosis - Extreme cases: Death  SKELETAL MUSCLE DISEASE III. EXERTIONAL MYOPATHIES Capture myopathy - Acute fatal myopathy of wild animals and birds - Preceded by chase struggle or transport - Pathogenesis similar to azoturia - Lesions observed: - Degeneration of the muscle - Hemorrage - Tendon rupture  SKELETAL MUSCLE DISEASE III. EXERTIONAL MYOPATHIES Compartment syndrome - Degeneration/necrosis of muscles surrounded by heavy aponeurosis - Typical of poultry - Muscular expansion in a non-expandable compartment - Vascular compression - Ischemia - Infarction of the muscle fibers  SKELETAL MUSCLE DISEASE IV. TRAUMATIC MYOPATHIES A. Downer Cow Syndrome - Ischemic necrosis of ventral limb muscles due to recumbence - Disease/anesthesia - Mainly in mature animals (bigger mass) Prostration - Vicious circle: Muscle Injury injury Very weak animals or Not able to stand Affected muscle will repair partially. Extensive scars Ischemia Edema Venous Compression occlusion  SKELETAL MUSCLE DISEASE TRAUMATIC MYOPATHIES Downer cow syndrome  SKELETAL MUSCLE DISEASE IV. TRAUMATIC MYOPATHIES B. Crush syndrome - Acute degenerative myopathy - All species - Severe trauma of a muscle group - Usually kidneys affected as well  SKELETAL MUSCLE DISEASE IV. TRAUMATIC MYOPATHIES C. Post-anesthetic myopathy - 3-6% of anesthetic cases - Severity varies from muscle swelling - Lameness to paresis - Possible renal failure and shock - Possible permanent loss of muscle function  SKELETAL MUSCLE DISEASE A. Developmental abnormalities B- Degenerative alterations: Atrophy (3 types) - Denervation atrophy - Disuse atrophy - Malnutrition atrophy Hypertrophy Muscle degeneration and necrosis Calcification C- Muscle repair: Regeneration D- Myopathies E- Myositis  SKELETAL MUSCLE DISEASE E. MYOSITIS - Bacterial - Black leg - Gas gangrene - Botulism* - Tetanus* - Viral - Foot and mouth disease (Skin pathologies) - Parasitic - Trichinosis - Cysticercosis - Sarcocystosis - Idiopathic-immune mediated - Masticatory muscle myositis - Myasthenia gravis - Neoplastic - Rhabdomyoma and rhabdomyosarcoma  SKELETAL MUSCLE DISEASE Bacterial Myositis - Black leg (Symtomatic anthrax, emphysematous gangrene) - Acute fatal : Clostridium chauvoei - Infection: 1 Soil containing spores Ingestion 2 Spores in the GIT/liver muscle - Then: 3 Muscle injury Change of local environment Germination Exotoxins edema Myonecrosis emphysema toxemia death Pathology - Large masses of muscles (Pectoral, pelvic, crural, scapular…) - Muscles are black, with gas (emphysema) - Odor - Subcutaneous edema  SKELETAL MUSCLE DISEASE Bacterial Myositis - Black leg (Symtomatic anthrax, emphysematous gangrene)  SKELETAL MUSCLE DISEASE Bacterial Myositis - Black leg (Symtomatic anthrax, emphysematous gangrene)  SKELETAL MUSCLE DISEASE Bacterial Myositis - Black leg (Symtomatic anthrax, emphysematous gangrene) - Histopathology: - Degeneration - Edema - Necrosis - Emphysema - Difficult to see bacteria  SKELETAL MUSCLE DISEASE Bacterial Myositis Gas gangrene (Malignant edema) - Fatal infection (Clostridium septicum, perfringens, chauvoei…) - Ruminants, horses and pigs. (Sometiemes horses) - Entrance through a wound - Spores are present in soil and feces - Anaerobic bacteria> Deep wounds with low oxygen tension - Affected areas cold (live animals) - Crepitation - Toxemia - Prostration - Death  SKELETAL MUSCLE DISEASE Bacterial Myositis Gas gangrene (Malignant edema) - Gas cumulation - Severe edema - Hemoraghe - Discoloration Diagnosis requires laboratory test  SKELETAL MUSCLE DISEASE Bacterial Myositis Gas gangrene (Malignant edema) - Gas cumulation - Severe edema - Hemoraghe - Discoloration Diagnosis requires laboratory test  SKELETAL MUSCLE DISEASE Parasitic Myositis Trichinosis (Trichinella spiralis) - Zoonotic disease - Consumption of incomplete cooked meat (Pork, acuatic mammals) - Adult lives in the small intestine > Larvae migrates to the tissues - Larvae encysts in the muscle for years  SKELETAL MUSCLE DISEASE Parasitic Myositis Cysticercosis (Cysticercus ovis, bovis, cellulosae) - Zoonotic disease. - Cysticercus is larval stage of a taenia (Platyhelminth). - Adult lives in the small intestine (Carnivore) > Larvae lives in the muscle of an intermediate host (Ruminants). - Sometimes migration to the brain> Neurocysticercosis.  SKELETAL MUSCLE DISEASE Parasitic Myositis Sarcocystosis (Sarcocystis spp) - Zoonotic disease. - Ruminants, horses (Intermediate host). Definitive (carnivores) - Cyst contains trillions of parasites - Usually no inflammatory response in the muscle - Important general signs> Abortion  SKELETAL MUSCLE DISEASE Idiopathic – immune mediated myositis Masticatory muscle myositis - Dogs and bovines - Swollen painful jaws> Atrophy if persistent - Blood eosinophilia - Pathogenesis not completely understood (Allergy/Hypersensitivity - Bilateral lesions with infiltration of eosinophils in jaw muscles  SKELETAL MUSCLE DISEASE Idiopathic – immune mediated myositis Myasthemia gravis - Sporadic from dogs and cats - Weakness and severe muscular fatigue after mild exercise - No big microscopic changes - Megaesophagus, dysphagia, aspiration pneumonia… - Two types: Hereditary (reduced ACh receptors) Acquired: (antibodies against ACh receptors) - Treatment with Neostigmine (Anticholinesterase drugs) https://youtu.be/3bQXBT8iVys Before treatment https://youtu.be/JapOIFuVoNs After treatment  SKELETAL MUSCLE DISEASE Neoplasia - Primary - Rhabdomyoma/Rhabdomyosarcoma - Fibroma/Fibrosarcoma - Lipoma/Liposarcoma - Hemangioma/Hemangiosarcoma - Lymphoma/Lymphosarcoma - Secondary - Metastasis of sarcomas, carcinomas