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