NAVLE Musculoskeletal

Equine Myositis and Myopathy Study Guide

Equine myopathies and myositis represent a diverse group of muscle disorders that are frequently encountered in equine practice and constitute a significant portion of NAVLE examination content.

Overview and Clinical Importance

Equine myopathies and myositis represent a diverse group of muscle disorders that are frequently encountered in equine practice and constitute a significant portion of NAVLE examination content. These conditions range from acute exertional rhabdomyolysis ("tying up") to inherited metabolic disorders and toxic myopathies. Understanding the pathophysiology, clinical presentation, diagnosis, and management of these conditions is essential for veterinary practice.

The term rhabdomyolysis refers to the breakdown of skeletal muscle fibers with release of intracellular contents (myoglobin, creatine kinase, electrolytes) into the bloodstream. This can occur sporadically or as a chronic, recurrent condition with underlying genetic predisposition.

Category Conditions
Exertional Myopathies PSSM Type 1 and Type 2 Recurrent Exertional Rhabdomyolysis (RER) Myofibrillar Myopathy (MFM) Malignant Hyperthermia (MH)
Non-Exertional Myopathies Hyperkalemic Periodic Paralysis (HYPP) Immune-Mediated Myositis (IMM/MYHM) Nutritional Myodegeneration (White Muscle Disease)
Toxic Myopathies Atypical Myopathy (Europe - Sycamore maple) Seasonal Pasture Myopathy (North America - Box elder)

Classification of Equine Myopathies

Equine myopathies can be classified based on etiology and presentation:

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