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| + | ==Degeneration== |
| + | [[Image:Degenerate muscle fibres.jpg|right|thumb|100px|<small><center>Degenerate muscle fibres (Image sourced from Bristol Biomed Image Archive with permission)</center></small>]] |
| + | |
| + | *Different types of degeneration |
| + | *May, or may not, be reversible |
| + | *Cloudy swelling, hydropic, vacuolar, granular and fatty change |
| + | *Occur following many different types of insult and are usually '''segmental''' |
| + | *If regeneration does not occur after formation of small vacuoles, [[Muscles - degenerative#Necrosis|necrosis]] follows |
| + | **Vacuolation -> floccular degeneration -> granular degeneration -> [[General Pathology - Degenerations and Infiltrations#Hyaline Degeneration|hyaline]] and [[Zenker degeneration|Zenker’s degeneration]] |
| + | *[[General Pathology - Degenerations and Infiltrations#Vacuolar Degeneration|'''Vacuolar degeneration''']]: |
| + | **Due to swelling of organelles or due to glycogen or fat accumulation |
| + | **May be caused by hypokalaemia, hyperkalaemia or necrosis |
| + | *Histologically: |
| + | **Swollen |
| + | **Hypereosinophilic |
| + | **Lost cross striations |
| + | |
| + | |
| + | ===Calcification=== |
| + | |
| + | *Due to: |
| + | **Old age - myofibres |
| + | **Following necrosis - [[General Pathology - Pigmentation and Calcification#Dystrophic|dystrophic calcification]] |
| + | ***May be visible grossly as white foci |
| + | |
| + | |
| + | ===Ossification=== |
| + | |
| + | *Metaplasia of muscle to bone |
| + | *'''Localised''' |
| + | **Only in single muscle or a single group of muscles |
| + | **May be associated with trauma |
| + | **Seen in horses and dogs |
| + | **Histologically: |
| + | ***Central zone - proliferating undifferentiated cells and [[General Pathology - Chronic Inflammation#Fibroblasts|fibroblasts]] |
| + | ***Middle zone - [[Bones - normal#Normal structure|osteoblasts]] depositing osteoid and bone |
| + | ***Outer zone - [[Bones - normal#Bone organisation|trabecular bone]] remodelled by [[Bones - normal#Normal structure|osteoclasts]] |
| + | *'''Progressive''' (fibrodysplasia ossificans progressiva) |
| + | **In connective tissue associated with skeletal muscle |
| + | **Secondary involvement of muscle tissue |
| + | **In pigs and cats |
| + | **Histologically: |
| + | ***Bundles of dense fibrous connective tissue |
| + | ***May contain accumulations of cartilage, bone or calcium |
| + | **Hyperplastic connective tissue -> compression of adjacent skeletal muscle -> [[Muscles - degenerative#Atrophy|atrophy]] |
| + | |
| + | |
| + | ===Pigmentation=== |
| + | |
| + | *[[General Pathology - Pigmentation and Calcification#Lipofuscin|'''Lipofuscin''']] |
| + | **Wear and tear pigment accumulating in secondary lisosomes -> converted into compact residual bodies |
| + | **Due to old age, past or recent cachexia or starvation |
| + | **Mostly stored in skeletal muscle of old high producing dairy cattle |
| + | **Masseters and diaphragm mainly involved |
| + | **No clinical importance |
| + | **Histologically: |
| + | ***Rounded yellow to brown granules at both poles of nucleus of the skeletal myofiber |
| + | *[[General Pathology - Pigmentation and Calcification#Melanin|'''Melanin''']] |
| + | **As part of congenital melanosis of calves in fascial sheaths and epimysium |
| + | **Grossly - black foci |
| + | *'''Myoglobin''' |
| + | **After extensive muscle necrosis - '''rhabdomyolysis''' |
| + | **Leaks to adjacent tissue after sudden injury |
| + | *May also be present after some types of intramuscular injections e.g. iron dextran or tetracycline |
| + | |
| + | |
| + | ==Necrosis== |
| + | |
| + | *Necrosis of an entire myofibre is uncommon |
| + | *Segmental necrosis is more typical |
| + | *Muscle cell contents may leak into the blood if the cell membrane is damaged |
| + | *Creatine kinase (CK) is an enzyme which leaks following injury |
| + | **Used to measure the extent of muscle damage |
| + | *Often is followed by [[Muscles - normal#Regeneration|regeneration]] |
| + | *Histologically: |
| + | **Hyaline hypercontracted fiber rounded at cross-section and increased diameter and eosin staining |
| + | ***May also be an artifact due to hypercontraction of normal fibres at fixation |
| + | **Fragmenting portions of fibre -> floccular or granular |
| + | **Normal portion of fibre may detach from necrotic part -> retraction caps |
| + | **Infarction may cause '''discoid degeneration''' - necrotic fibres detach at '''Z lines''' |
| + | **May [[Muscles - degenerative#Calcification|mineralise]] |
| + | *[[Zenker degeneration|'''Zenker's degeneration''']] - secondary to systemic disease |
| + | **Scattered small segments of necrosis and fast regeneration |
| + | **Sacrolemmal tubes are intact |
| + | |
| + | |
| + | ==Atrophy== |
| + | [[Image:Atrophic muscle fibres.jpg|right|thumb|100px|<small><center>Atrophic muscle fibres (Image sourced from Bristol Biomed Image Archive with permission)</center></small>]] |
| + | |
| + | *Decreased myofibre or whole muscle diameter |
| + | *Myofibrils removed by disintegration -> sacrolemma too large -> forms folds |
| + | *Caused by: |
| + | **<u>'''Disuse'''</u> (e.g. fracture, failure to use limb, recumbency) |
| + | ***Slower than denervation atrophy |
| + | ***Reversible unless too prolonger or severe to cause loss of myofibres |
| + | **<u>'''Denervation'''</u> |
| + | ***Any interference or damage to its nerve supply results in muscle atrophy |
| + | ****Can be rapid - over 50% of muscle mass may be lost in a few weeks e.g. roarer horses with [[Larynx Degenerative - Pathology#Laryngeal hemiplegia|laryngeal hemiplegia]] |
| + | ***May be reversible if innervation re-established |
| + | ***Histologically: |
| + | ****Fibres become rounded in cross section unless compressed by normal fibres |
| + | ****Increased concentration of nuclei as they take much longer to disintegrate |
| + | ****Fibrous stroma of epimysium and endomysium condenses -> more prominent |
| + | ****End result in muscle consisting of almost only fibrous tissue |
| + | ***Sometimes replaced by fat tissue -> increased size of muscle = ''pseudohypertrophy'' |
| + | ***Muscle may have a mixture of atrophied and [[Muscles - hyperplastic and neoplastic#Hypertrophy|hypertrophied]] (due to increased work load) fibres if some motor units are not damaged |
| + | **<u>'''Metabolisation of muscle protein'''</u> for nutrients during: |
| + | ***Malnutrition, cachexia, senility |
| + | ***Gradual onset except for some febrile diseases causing cachexia |
| + | ***Postural muscles are not affected, sometimes even [[Muscles - hyperplastic and neoplastic#Hypertrophy|hypertrophy]] |
| + | ***Histologically: |
| + | ****Some nuclei disappear as myofibre volume is decreased |
| + | ***Grossly: |
| + | ****Smaller, darker, thinner muscles |
| + | |
| + | |
| + | ==Toxic myopathy== |
| + | |
| + | *'''Plants''' |
| + | **E.g. ''Cassia occidentalis'' (coffee senna), ''Karwinskia humboldtiana'' (coyotillo), ''Eupatorium rugosum'' (white snakeroot), cotton seed |
| + | **Lesion an skeletal and cardiac muscle |
| + | **Grossly: |
| + | ***Pale areas with ill-defined borders |
| + | ***May involve very extensive [[Muscles - degenerative#Necrosis|necrosis]] |
| + | **Histologically: |
| + | ***Segmental necrosis, no calcification |
| + | ***[[Muscles - normal#Regeneration|Regeneration]] may occur in surviving animals |
| + | *'''Drugs''' |
| + | **E.g. corticosteroids, cholinesterase inhibitors, vincristine, dimethyl sulfoxide (DMSO) |
| + | **'''Monensin''' is a coccidiostat toxic to horses, donkeys, zebras, cattle, sheep, dogs and birds |
| + | ***Causes muscle necrosis in heart and skeletal muscle |
| + | ***Grossly: |
| + | ****Pale streaks, mostly in hind limbs |
| + | ***Histologically: |
| + | ****[[Muscles - degenerative#Necrosis|Segmental necrosis]] |
| + | ****Possibly [[Muscles - normal#Regeneration|regeneration]] in surviving animals |
| + | ***Can cause rapid onset recumbency and potentially death |
| + | ***Usually due to mixing errors in feed |
| + | **Also from intramuscular injections, e.g. oxytetracycline, lidocaine, chloramphenicol, produce local necrosis |
| + | ***As [[Muscles - normal|satellite cells]] are destroyes, repair is via fibrosis with some [[Muscles - normal#Regeneration|budding]] |
| + | *'''Chemicals''' |
| + | **Iron injections can cause local myonecrosis |
| + | *'''Mycotoxins''' |
| + | **Metabolites cause persistent tremors |
| + | **Lesions in skeletal muscle only, possibly secondary to sustained contractions (similar to [[Muscles - degenerative#Exertional myopathies|exertional myopathy]]) |
| + | **Histologically: |
| + | ***Tiny foci of [[Muscles - degenerative#Necrosis|segmental necrosis]] |
| + | |
| + | |
| + | ==Endocrine myopathy== |
| + | |
| + | *[[Adrenal Glands - Pathology#Adrenal Hyperfunction|Hyperadrenocorticism]] |
| + | **Muscle weakness is a clinical sign |
| + | **-> [[Muscles - degenerative#Atrophy|muscle atrophy]] |
| + | ***Type II myofibre atrophy is non-specific |
| + | ***Type IIB myofibre atrophy is preferential in hyperadrenocorticism |
| + | *[[Thyroid Gland - Pathology#Hypothyroidism|Hypothyroidism]] can cause muscle atrophy |
| + | |
| + | |
| + | ==Nutritional myopathy== |
| + | [[Image:White muscle disease.jpg|right|thumb|100px|<small><center>White muscle disease (Image sourced from Bristol Biomed Image Archive with permission)</center></small>]] |
| + | [[Image:White muscle disease histo.jpg|right|thumb|100px|<small><center>White muscle disease (Image sourced from Bristol Biomed Image Archive with permission)</center></small>]] |
| + | |
| + | = [[White muscle disease|'''White muscle disease''']] |
| + | *Very important economic disease of sheep, cattle and pig |
| + | *Caused by: |
| + | **Deficiency of selenium, vitamin E or both |
| + | **Exacerbated by rapid growth, unaccustomed exercise or other dietary factor |
| + | *Pathogenesis: |
| + | **Oxygen free radicals (OFR) can damage cell membranes |
| + | **Vitamin E usually mops up OFRs |
| + | **Selenium as part of glutathione peroxidase neutralises effects of OFRs |
| + | **If Vit E or Se are deficient -> the balance shifts to membrane damage, calcium entry and mitochondrial damage -> cell swells and dies -> segmental muscle [[Muscles - degenerative#Necrosis|necrosis]] |
| + | *Grossly: |
| + | **Lesions are bilaterally symmetrical in hard working muscles (vary with species) |
| + | **Early lesions are pale areas and streaks |
| + | ***Difficult to see especially in pale muscles |
| + | **Later becoming calcified necrotic areas |
| + | ***More obvious |
| + | **Pigs also have lesions in their [[Myocardial - Pathology#Hyaline degeneration|heart]] and [[Liver - general pathology#Hepatosis dietica|liver]] |
| + | *Histologically: |
| + | **[[Muscles - degenerative#Necrosis|Segmental necrosis]] +/- [[Muscles - degenerative#Calcification|calcification]] and [[Muscles - normal#Regeneration|regeneration]] |
| + | **Multifocal and multiphasic lesions |
| + | |
| + | ==Exertional myopathies== |
| + | |
| + | *Caused by intensive and exhaustive activity of major muscle masses |
| + | *Glycogen used up -> local heat and lactic acid -> muscle degeneration |
| + | *Other forms include '''capture myopathy''', racing greyhounds, sheep chased by dogs |
| + | |
| + | |
| + | ===Equine rhabdomyolysis=== |
| + | |
| + | *'''Azoturia''' (Monday morning disease) |
| + | **Acute |
| + | **Due to exercise following a prolonged period of rest |
| + | **Clincal signs: |
| + | ***Unable to move |
| + | ***Sweating |
| + | ***Tremors |
| + | ***Swollen and hard lumbar, gluteal and femoral muscles |
| + | **Myoglobin leaks from muscle cells -> leaks into urine -> urine is dark red/brown (myoglobinuria) -> damages renal tubules |
| + | **Grossly: |
| + | ***Salmon pink muscles -> dark, moist, swollen +/- pale streaks |
| + | **Histologically: |
| + | ***Segmental myofibre [[Muscles - degenerative#Necrosis|necrosis]] |
| + | ****Multifocal and monophasic, but may be multiphasic if repeated bouts |
| + | ***Both, type IIA and IIB fibres affected; type IIB preferentially affected in acute disease |
| + | ***Minor inflammatory reaction and calcification |
| + | |
| + | *'''Tying-up''' |
| + | **Similar to azoturia but much milder |
| + | **Grossly - normal muscle |
| + | **Histologically - same as azoturia |
| + | |
| + | |
| + | ===Porcine stress syndrome=== |
| + | |
| + | *='''Malignant hyperthermia''' |
| + | *Pigs, dogs, humans |
| + | *Possibly a cellular defect resulting in high intacellular calcium ion concentration |
| + | **-> Activates myofibrillar ATPase -> rapid intracellular glycolysis -> increase in body heat -> denature protein -> cell death -> leakage of cellular content -> oedema |
| + | *Grossly: |
| + | **Muscles are pale, soft and exudative |
| + | *Histologically: |
| + | **Segmental hypercontraction |
| + | **Monophasic, multifocal [[Muscles - degenerative#Necrosis|segmental necrosis]] |
| + | *Inherited |
| + | *Triggered by halothane anaesthesia, stress of handling, transportation or slaughter |
| + | |
| + | |
| + | ==Neuromuscular junction diseases== |
| + | |
| + | ===Aquired myasthenia gravis=== |
| + | |
| + | *See [[Muscles Developmental - Pathology#Myasthenia gravis (MG)|congenital MG]] |
| + | |
| + | |
| + | ===Botulism=== |
| + | |
| + | *Caused by: |
| + | **Ingestion of [[Clostridium species|''Clostridium botulinum'']] toxin which inhibits acetyl choline release |
| + | *Diagnosis by demonstration of toxin in faeces, ingested material or serum |
| + | |
| + | |
| + | ==Circulatory disturbances== |
| + | |
| + | ===Congestion=== |
| + | |
| + | *Localised or generalised stasis -> dark red muscle |
| + | *E.g. in ruminal tympany ([[Forestomach - Nutritional Pathology#Bloat/ Tympany|bloat]]) - congestion of muscles cranial to thoracic inlet |
| + | *May resemble haemorhage grossly |
| + | |
| + | |
| + | ===Ischaemia=== |
| + | |
| + | *Firstly [[Muscles - degenerative#Necrosis|segmental necrosis]] |
| + | *-> death of satellite cells |
| + | **Causes [[Muscles - normal#Regeneration|regeneration]] but myoblast precursors have to be recruited from viable fibres |
| + | *-> death of all cells |
| + | *Mostly healed by fibrosis and scar formation |
| + | *May attempt regeneration by [[Muscles - normal#Regeneration|budding]] |
| + | Main causes: |
| + | *'''Vascular occlusion''' |
| + | **Infarction from embolism is rare due to collateral circulation |
| + | **Extension of infarcts depends on size of vessels occluded |
| + | ***Small capillaries -> segmental [[Muscles - degenerative#Necrosis|necrosis]] |
| + | ***Large arteries -> whole muscle areas, including sattelite cells, are killed |
| + | **Healed by fibrosis |
| + | **May be due to: |
| + | ***Blockage of iliac arteries by aortic-iliac thrombosis in horses |
| + | ***Blockage of aortic bifurcation in cats |
| + | ***[[Dirofilaria immitis|''Dirofilaria immitis'']] arteritis in dogs |
| + | ***Vasculitis due to [[Reoviridae#Bluetongue Virus|bluetongue virus]] in sheep |
| + | ***[[General Pathology - Haemorrhage#Purpura haemorrhagica|'''Equine purpura haemorrhagica''']] |
| + | ****Non-contagious, sporadic |
| + | ****Grossly: |
| + | *****Subcutaneous oedema |
| + | *****Scattered haemorrhagic foci throughout skin and muscles |
| + | *****Vasculitis -> infarcts of muscles |
| + | ****May cause myoglobinuria if extensive |
| + | ****Possibly immune mediated |
| + | ****In horses post [[Streptococci|streptococal]] infection, especially [[Respiratory Bacterial Infections - Pathology#Strangles|strangles]] |
| + | *'''External pressure''' |
| + | **During prolonged recumbency, e.g. anaesthesia, inability to rise, or due to too tightly fitting bandages or casts |
| + | **Post anaesthesia myopathy especially in horses |
| + | ***Dorsal recumbancy -> gluteals and longissimus ischaemia |
| + | ***Lateral recumbancy -> triceps brachii, pectoralis, deltoideus and brachiocephalicus ischaemia |
| + | **Caused by pressure on muscle > perfusion pressure of capillaries |
| + | **Downer cows - vetral recumbency -> ischaemia of pectoral muscles and muscles of limbs tucked under the animal |
| + | **Pregnant ewes with twins or triplets -> internal abdominal oblique muscle ischaemic necrosis -> potential rupture |
| + | *'''Muscle swelling''' where it cannot expand |
| + | **E.g. supracoracoid muscle infarction in some breeds of turkeys after flapping their wings |
| + | ***Surrounded by inelastic fascial sheath and bone |
| + | |
| + | ==Trauma== |
| + | |
| + | *Due to: |
| + | **Direct transection of myofibres |
| + | **Compression of myofibres |
| + | **Secondary from haemorrhage (bruising) |
| + | ***May increase muscle pressure -> [[Muscles - degenerative#Ischaemia|ischaemia]] -> [[Muscles - degenerative#Necrosis|necrosis]] |
| + | **Partial rupture - ''e.g.'' of diaphragm in road traffic accident |
| + | **Complete rupture - ''e.g.'' quadriceps of racing greyhounds |
| + | **Myorrhexis (tearing) - ''e.g.'' slippery floor causing 'splits' in cattle -> adductor muscle tear |
| + | *Healing is by [[Muscles - normal#Regeneration|regeneration]] |
| + | *Fibrosis (scarring) will compromise function |
| + | *During [[Bones Fractures - Pathology|fractures]], fragments may cause further trauma if moved |