Pathology of the Musculoskeletal System PDF

# Pathology of the Musculoskeletal System ## Introduction * **Higher Colleges of Technology** * **Systemic Pathology** * **2019-2020** ### Skeletal Muscle Structure * **Skeletal:** * Elongated myofiber cells * Multinucleated cells (100-300) * Nucleus remains peripheric * Non bran...

# Pathology of the Musculoskeletal System ## Introduction * **Higher Colleges of Technology** * **Systemic Pathology** * **2019-2020** ### Skeletal Muscle Structure * **Skeletal:** * 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) * **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 ### 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 mitochondria. * **Type II:** White, Fast twitch and fast fatigue. Energy comes from glycolysis. Two subtypes. ### 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 * 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 ### Skeletal Striated Muscle Disease * Development disease * Degenerative disease * Inflammatory disease * Neoplasia ### Possible Clinical Signs * Atrophy * Hypertrophy * Swelling * Weakness * Pain * Muscle spasm * Abnormal gait ### Disease Portal Entries For Skeletal * Wounds * Intramuscular injections * Bone fracture creating trauma * External pressure * Blood pathogens, toxins, autoantibodies... * Inflammatory ### Developmental Abnormalities * **Atrophy (3 types):** * Denervation atrophy * Disuse atrophy * Malnutrition atrophy * Hypertrophy * Muscle degeneration and necrosis * Calcification ### Muscle Repair: Regeneration * Macrophages clean the cell debrids within * Sarcolemmal tubes (Endoysium+ basal lamina)> Scaffold for the myoblasts. They prevent fibroblasts to mix with them. * Myoblasts undergo mitosis>creation of new sarcomeres * If sarcolemmal tubes break, fibrosis develops ### Degenerative Alterations * **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 * **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 * **Muscle degeneration and necrosis:** * Sequel to myofiber injury * Can be reversible to a point of 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. * **Calcification:** * Deposition of Ca++ * Common to muscle degeneration and necrosis * Calcified fibers look granular and bluish granules resembling bacteria * Special stain ### Myopathies * **Nutritional:** * White muscle disease (Nutritional myodegeneration) * **Metabolic:** * Porcine stress syndrome * **Exertional:** * 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 * 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 * Hemorrhage * Tendon rupture * Tying Up: * 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 * 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 * **Traumatic:** * Ischemic necrosis of ventral lymph muscles due to recumbence * Disease/ anesthesia * Mainly in mature animals (bigger mass) * Vicious circle: * Prostration * Injury * Ischemia * Venous occlusion * Compression * Muscle injury * Edema * Very weak animals or not able to stand, with extensive scars. The affected muscle will repair partially. * Crush syndrome: * Acute degenerative myopathy * All species * Severe trauma of a muscle group * Usually kidneys affected as well * Post anesthesia 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 ### Myositis * **Viral:** * Foot and mouth disease (Skin pathologies) * **Parasitic:** * Trichinosis (Trichinella): * Zoonotic disease * Consumption of incomplete cooked meat (pork, aquatic mammals) * Adult lives in the small intestine> Larva migrates to the tissues * Larvae encysts in the muscle for years * 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. * Sarcocystosis: * Zoonotic disease * Ruminants, horses (Intermediate host). Definitive (carnivores) * Cyst contains trillions of parasites * Usually no inflammatory response in the muscle. * Important general signs> Abortion * **Idiopathic-immune mediated:** * Masticatory muscle myositis * Myasthenia gravis * Rhabdomyoma and rhabdomyosarcoma * ### Bacterial Myositis * Black leg (Symtomatic anthrax, emphysematous gangrene): * Acute fatal: _Clostridium_ chauvoei * Infection: Soil containing spores * Spores in the GIT/liver * Muscle injury: Change of local environment edema, myonecrosis, emphysema toxemia * Pathology: * Large masses of muscles (Pectoral, pelvic, crural, scapular...) * Muscles are black, with gas (emphysema) * Odor * Subcutaneous edema