This is a diverse and complex cluster of disorders associated with terms that may be confusing due to their similarity. Some brief definitions may be in order. Myopathy can refer to any disease or abnormal condition of striated muscle. The term Myopathic simply refers to a disease of muscle tissue.
Hypotonia refers to reduced tension, relaxation, and loss of tone.
Hypertonia refers to increased tension, a stiffening or rigidity. The term tetany is also used to describe intermittent tonic spasms or rigidity. Most of the disorders discussed at this site are myopathies in some sense. The exception being those disorders which have a predominantly neurological origin, as in the Sleep Disorders , and some of the metabolic disorders, many of which can also be classified as myopathies. In general, I have divided up these disorders into major categories for more convenient reference.