Pathophysiology of Muscle Disorders in Horses

A set of flashcards covering key concepts related to the pathophysiology of muscle disorders in horses, including types of myopathies, their causes, clinical signs, and treatments.

What are the two main types of myopathies discussed in the lecture?

Exertional and Non-exertional myopathies.

What is 'tying up' also known as?

Sporadic rhabdomyolysis, monday-morning disease, or azoturia.

What causes sporadic rhabdomyolysis in horses?

Overexertion and dietary imbalances, such as low sodium, calcium, and vitamin E.

Which breeds are most commonly affected by PSSM-1?

Continental European draft breeds, especially Percheron and Belgian.

What is a common test to confirm PSSM?

Muscle biopsy to check if amylase successfully breaks down glycogen.

What is Recurrent Exertional Rhabdomyolysis (RER)?

An intermittent form of rhabdomyolysis linked to abnormal calcium regulation in myofibers.

Which hormone is linked to the increased risk of RER in horses?

Epinephrine (adrenaline).

What is HYPP and which breed is it associated with?

Hyperkalemic periodic paralysis, usually associated with Quarter Horses.

What are clinical signs of HYPP?

Sporadic stiffness, muscle tremors, weakness, breathing difficulties, and prolapse of the third eyelid.

What is myofibrillar myopathy?

A condition where the myofibril does not maintain the proper position for contraction.

What causes Non-Exertional immune-mediated myopathy?

It is usually associated with respiratory infections like Streptococcus or viral infections.

What is atypical myopathy associated with?

Ingestion of toxins from plants like box elder, which contain Hypoglycin A.

What is the mechanism behind atypical myopathy?

It inhibits the β-oxidation pathway, affecting aerobic metabolism.

What clinical signs are seen in horses with atypical myopathy?

Stiffness, muscle fasciculations, weakness, and myoglobinuria.

How is myonecrosis commonly caused in horses?

By Clostridial infections following injections or puncture wounds.

What are common clinical signs of myonecrosis?

Fever, stiffness, severe pain, and crepitation.

What are the main risk factors for polysaccharide storage myopathy (PSSM-1)?

Breed and exercising for more than 20 minutes in one session.

What is the primary genetic mutation causing PSSM-1?

A mutation in the GY1 gene affecting glycogen storage.

Which breed shows a high prevalence of PSSM-2?

Quarter Horses, with an approximate prevalence of 28%.

What is the significance of desmin proteins in myofibrillar myopathy?

Abnormal desmin proteins cannot support the Z-disk in the contractile apparatus.

What is the effect of low vitamin E intake in horses?

It leads to a poor antioxidant state, increasing muscle disorders.

What electrolyte imbalances are important for muscle contraction?

Sodium and calcium.

What is the role of the SERCA receptor in muscle function?

It allows removal of calcium from the sarcoplasm, leading to muscle relaxation.

What does a 'leaky' sodium channel cause in horses prone to HYPP?

Prolonged depolarization and abnormal action potentials in muscle cells.

How can exposure to toxic plants impact horse muscle health?

It can lead to rhabdomyolysis and muscle damage.

What is a classic clinical sign of toxic plant ingestion?

Rapid onset of muscle stiffness and weakness, sometimes with myoglobinuria.

What is the typical age range for diagnosis of PSSM-1 in horses?

4 to 8 years old.

What is the primary treatment for atypical myopathy?

To flush the system with fluids, although outcomes may vary.

What condition is PSSM-1 often confused with due to performance signs?

Sporadic rhabdomyolysis.

What should be considered when diagnosing muscle disorders?

Season, exercise routine, diet, and recent infections.

What is the recovery approach for recurrent exertional rhabdomyolysis?

Management of diet and exercise, focusing on gradual intensity increase.

What muscle condition may follow after an equine respiratory infection?

Immune-mediated myopathy or purpura hemorrhagica.

What are common signs of immune-mediated myopathy?

Lethargy and rapid muscle atrophy.

What significant risk factor increases the severity of muscle disorders?

Lack of proper pre-exercise conditioning.

What is the prevalent condition in draft horses related to exertional myopathies?

Polysaccharide storage myopathy (PSSM).

Which horse breeds are least affected by PSSM?

Light breeds like Standardbreds, Thoroughbreds, and Arabians.

How does a high potassium diet impact horses with HYPP?

It worsens their clinical signs.

Name an acquired condition that can lead to muscle atrophy.

Traumatic atrophy due to lack of innervation or immune-mediated myopathy.

What might you find in the clinical history of a horse with myonecrosis?

Recent dirty intramuscular injections.

What are the effects of severe muscle damage on a horse's performance?

Poor performance, reluctance to move, stiffness, and pain.

What is the importance of monitoring electrolyte levels in exercising horses?

To ensure proper muscle function and prevent exertional myopathy.

What is the recommended control for horses at risk of atypical myopathy?

Management of pasture access to prevent ingestion of toxic plants.

What is the therapeutic approach for immune-mediated myopathy?

Anti-inflammatories and managing underlying infections.

What role does calcium play in muscle contraction and relaxation?

Calcium release triggers contraction, while calcium removal allows relaxation.

What strategies can be employed to prevent myopathies in competitive horses?

Adequate training, nutritional management, and observation of early signs.

What should horse owners look for in performance indicators?

Monitoring changes in mobility, gait, activity level, and muscle condition.