Ischemic myopathy

In the early 1940s, the effect of induced ischemic myopathy on renal perfusion in the rabbit was studied. It was conclusively demonstrated in fhis model that there was extreme renal cortical vasoconstriction with preservation of the medullary circulation [7]. This early first demonstration of posttraumatic vasomotor nephropathy was independently confirmed 20 years later in the USA when preferential renal cortical ischemia was demonstrated in acute renal failure in man. Since then, many animals have been used to study... 

Glycogenosis type VIII (phosphorylase b kinase deficiency) gives rise to myopathy and liver disease, either singly or in combination. Phosphorylase b kinase (PBK) converts the inactive b form of both muscle and liver phosphorylases to the active a forms of the enzymes. The ischemic lactate test sometimes shows a flat result as in McArdle s disease, but is more likely to be normal. Histochemical demonstration of myophosphorylase activity in tissue sections shows a near-normal reaction due to the presence of phosphorylase a. Accumulation of glycogen is modest and found mainly in type 2 (fast-twitch glycolytic) muscle fibers. 

Deficiency of the muscle-specific myoadenylate deaminase (MADA) is a frequent cause of exercise-related myopathy and is thought to be the most common cause of metabolic myopathy. MADA catalyzes the deamination of AMP to IMP in skeletal muscle and is critical in the purine nucleotide cycle. It is estimated that about 1-2% of all muscle biopsies submitted to medical centers for pathologic examination are deficient in AMP deaminase enzyme activity. MADA is 10 times higher in skeletal muscle than in any other tissue. Increase in plasma ammonia (relative to lactate) after ischemic exercise of the forearm may be low in this disorder, which is a useful clinical diagnostic test in patients with exercise-induced myalgia... 

The major risk associated with -aminocaproic or tranexamic acid therapy is intravascular thrombosis as a direct result of the inhibition of plasminogen activator. Thrombi that form during therapy are not easily lysed and, therefore, can have additional ischemic consequences. Additional possible complications include hypotension, abdominal discomfort, and rarely, myopathy and muscle necrosis. 

Inflammatory myopathies include a heterogeneous group of acquired and potentially treatable disorders caused by an autoimmune process (idiopathic inflammatory myosites) or infectious agents (pyo-myositis). Among ischemic conditions, we focus here mainly on diabetic muscle infarction and rhab-domyolysis. As previously stated, compartment syndromes are addressed in Chapter 15. 

---