Which condition features continuous muscle cramps and myoglobinuria?

McArdle's disease, a type of glycogen storage disease, is characterized by the body's inability to properly break down glycogen due to a deficiency of the enzyme myophosphorylase. In individuals with this condition, exercise or physical exertion can lead to continuous muscle cramps and myoglobinuria, the latter being the presence of myoglobin in the urine, which occurs as a result of muscle breakdown.

During physical activity, the lack of available energy due to impaired glycogen metabolism results in muscle fatigue, pain, and cramping. When muscle tissue is damaged, myoglobin leaks into the bloodstream and is subsequently excreted in the urine, leading to myoglobinuria, which can be detected as dark-colored urine.

In contrast, Becker's muscular dystrophy primarily affects muscle fibers and leads to progressive muscle weakness but does not typically result in muscle cramps and myoglobinuria. Myasthenia gravis is an autoimmune disorder affecting neuromuscular transmission, leading to muscle weakness and fatigue rather than cramps or myoglobinuria. Multiple sclerosis is a demyelinating disease of the central nervous system that may cause a variety of neurological symptoms but is not characterized specifically by muscle cramps and myoglobinuria.