A myopathy is any disease that compromises muscle tissue, according to Health Grades. It may produce spasms, inflammation or paralysis and may be acquired or inherited.
Cramps and stiffness are common forms of an acquired myopathy, which is typically the result of an electrolyte imbalance, dehydration or muscle fatigue, Health Grades explains. Acquired myopathies may also occur in individuals who come into contact with an infectious property, such as a virus or bacteria.
An inherited myopathy stems from a congenital or genetic disorder and can result in dysfunction and progressive weakness. In some cases, it is impossible to determine the source of a myopathy because no obvious risk factors exist, states Health Grades.