Skeletal Muscle Flashcards by Stephanye Quinn

White Muscle Disease is caused by

Vitamine E / Se deficiency

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Pathogenesis of Malignant Hyperthermia

Inherited defect in skeletal muscle ryanodine receptor
Excessive Ca release and contraction when stimulated
Heat production and myocyte necrosis

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Disease

Exertional Rhabdomyolysis

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Disease

White Muscle Disease

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Causes of monophasic lesions of skeletal muscle

Trauma - will be focal

Exertion - Capture myopathy

Toxin - ionophores, plants

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MDx

Rhabdomyosarcoma

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Myocytes increase in size by

Addition of Myofilaments

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MDx

Diffuse eosinophilic myositis

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Disease

Splay Leg

Swimmer Syndrome

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T/F: Atrophy can be the result of another pathological process affecting the muscle

True

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MDx

Polyphasic myocyte degeneration and necrosis with dystrophic calcification

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What types of causes incite this pattern of degeneration and necrosis?

Polyphasic lesion causes:

Nutritional deficiency - Vitamin E/Se

Ongoing toxicities

Genetic defects in myocyte structure/metabolic elements

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Pathogenesis of Botulism

Decaying organic matter
Clostridium botulinum thrives and elaborates into environment
Ingested
Toxin inhibits Ach release from nerve terminals at neuromuscular junction
Progressive generalized paralysis with death by cardiorespiratory failure

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Disease

Compartment Syndrome

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Muscular Dystrophy

X linked inhereted myopathy reported in dogs and cats (especially goldens)

Defects in dystrophin gene - cytoskeleton protein

No treatment

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Pathological process that accounts for this appearance?

Degeneration / Necrosis

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Lesions caused by White Muscle Disease are seen in (Active/Inactive) Muscle

Active

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MDx

Focal Muscle Degeneration and Necrosis

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Disease

Black Leg

Clostridium chauvoie infection

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Why is it important to use special stains when diagnosising sarcomas?

To differentiate between sarcomas - each type behaves differently

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MDx

Atrophy

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Describe morphological problem

Muscle is pale, swollen and dry to the touch

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MDx

(Rear leg of dog)

Hemangiosarcoma

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MDx

Myocyte Hypoplasia

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Pathogenesis of Infarction

* Recumbancy * Increased intramuscular pressure * Poor perfusion * Ischemia * Infarction

Possible cause of eosinophilic myostis in a dog

Masticatory Myositis

Pathogenesis of Black Leg (Clostridium chauvoei infection)

* Ingestion of spores * Dissemination to muscle via blood * Latency * Tissue hypoxia/acidosis * Bacterial proliferation * Production of exotoxins * Myonecrosis and systemic endothelial damage * Death from septicemic shock

Exertional Rhabdomyolysis

Necrosis/lysis of skeletal muscle Ionic events of contraction can produce adverse environment May have underlying metabolic condition which predispose - polysaccharide storage disease

MDx

Intramuscular hemorrhage

What typically causes this pattern of necrosis?

Acute Toxicity Exertion

Cause

Damage to the Left Recurrent Laryngeal Nerve

T/F: Cuase of muscle injury can be determined by histopathology alone

False; supplemental tests and clinical history are usually required

Cause

Trauma - penetrating wounds, fractures

What do myofibers do when they are hurt?

Die Regenerate

MDx

Rhabdomyosarcoma

Morphological Diagnosis?

Muscle Infarct

Describe the lesion

Fibrosis and fiatty infiltration (steatosis) of skeletal muscle

Causes of myocyte hyperplasia

Double Muscling Inactivation of the regulatory gene myostatin - involved in myoblast cell progression to muscle fibers

MDx

Acute necrotic and hemorrhagic myositis

Disease

White Muscle Disease

Azoturia

Excess nitrogen in urine

MDx | (Rear leg of dog)

Rhabdomyosarcoma

Causes of myositis

Necrotic / hemorhhagic = Clostridium chauvoei, Clostridium septicum Suppurative - Pyogenic bacteria Lymphocytic - Immune- Mediated Eosinophilic - Active protozoal / parasitic infections, immune mediated Granulomatous

"Biochemical" pathological processes resulting in severe muscular clinical signs

Neuromuscular Junction Disorders Electrolyte Disorders Inherited disorders of Muscle Metabolism - Myotonias

What cell type do neoplasms with striaged muscle differentiation (rhabdomyoma/sarcoma) derive from?

Gross morphological diagnosis?

Skeletal muscle degeneration and necrosis Rhabdomyolysis

Fibrosis and fatty infiltration (steatosis) often develops in what chronic skeletal muscle condition

Atrophy

Causes of myocyte hypertrophy

Exercise conditioning Compensatory - decreased number/size of functional myocytes, increased load on remaining

Describe the lesion

Muscles are dark red, swollen, soft/friable/ palpable crepitus

MDx

Focal Suppurative myositis

Pathogenesis of Compartment Syndrome

* Rapid muscle growth * Period of increased circulation (exertional) * Muscle swelling confined by facia * Impedes blood supply * Ischemia * Infarction

What pattern of necrosis is this?

Monophasic

MDx

Chronic eosinophilic myositis and muscle atrophy

What pathological process could account for this appearance?

Degeneration and Necrosis Inflammation and Repair Circulatory Disorder

Disease

Splay Leg Swimmer Syndrome

Causes of skeletal muscle atrophy

Physiologic - disuse/aging Cachexia/ Malnutrition Endocrine disease - myocytes have surface receptors for hormones Denervation - myocyte maintencance requires trophic factors generated at neuromuscular junction - occurs quickly

Histological characteristics of myofiber regeneration

Internalization of nuclei Macrophage infiltrate

Histologic characteristics of myofibers that die

Vaculation of sarcoplasm Condensation of sarcoplasm Nuclear pyknosis Calcification

MDx

Focal monophasic myonecrosis

Disease

Laryngeal Paralysis

Pathogenesis of Polyphasic Skeletal Muscle Degneration caused by nutritional deficiency

* Vitamine E/Se Deficiency * Needed for enzymes like glutathione peroxidase / reductase * Lack of ability to scavange free radicals * Oxidative damage - lipoperoxidation of cell membranes * Myocyte injury

What is morphologically abnormal?

Decreased striations Necrosis Hypnotic nuclei Neutrophil infiltration

What 3 Pigments and tissue deposits are observed in skeletal muscle?

Lipofuscin Exogenous Pigments Dystrophic Calcification

MDx

Polyphasic monocyte degeneration and necrosis, chronic, with hypertrophy, atrophy and fibrosis

Capture Myopathy

Zoo and Wild Birds Due to exertion, stress during capture/handling/transport Anaerobic glycolysis leads to hyperthermia and metabolic acidosis

Endogenous Pigments seen in skeletal muscle

Hematogenous Pigments (Hemoglobin, Hemosiderin, Bilirubing, Porphyria) Melanin Lipofuscin

Type of skeletal muscle lesion

Monophasic Lesion

Pathological process to account for this appearance?

Disorders of Growth

T/F: Malignant hyperthermia is an example of a metabolic condition predisposing to necrosis

True