|Vacuolar Myopathy (VM)|
Vacuolar Myopathy (VM) is a very rare form of exercise intolerance, with only one case reported in the published literature. The clinical signs manifesting during or after exercise resemble other types of exertional rhabdomyolysis. During an episode, horses are reluctant to move, experience pain, stiffness, and tremors, and sweat profusely. Serum creatine kinase (CK) and aspartate aminotransferase (AST) are elevated, indicating muscle damage. In severe episodes, pigmenturia (coffee-colored urine due to the presence of myoglobin), inability to stand, and death can occur. These symptoms resemble other forms of exercise intolerance such as Polysaccharide Storage Myopathy (PSSM), Recurrent Exertional Rhabdomyolysis (RER), and Myofibrillar Myopathy (MFM).
Vacuolar Myopathy (VM) is distinct from these other forms of exercise intolerance with respect to findings on muscle biopsy. Histopathology shows abundant sarcoplasmic vacuoles of various sizes containing proteinaceous debris. Many vacuoles are devoid of glycogen and there is no amylase-resistant polysaccharide. Vacuoles do not stain for mitochondrial succinate dehydrogenase, mitochondrial cytochrome oxidase, or acid phosphatase.
Vacuolar Myopathy (VM) is presumed to be an inherited condition, although the genetic basis is currently unknown.
Date of Last Update: 08/02/2016
The mode of inheritance of Vacuolar Myopathy (VM) is currently unknown.