M63.8: Other disorders of muscle in diseases classified elsewhere

M63.8 describes a cluster of medical conditions where the muscular system is affected secondary to another disease or condition classified elsewhere. The muscular disorders under M63.8 are not stand-alone conditions but are instead linked to other diseases, such as metabolic or hormonal disorders, or systemic conditions such as lupus or rheumatoid arthritis. Symptoms of these muscle disorders are varied but may include muscle weakness, stiffness, cramps, or spasms. The progression of this disorder may also differ depending on the root cause. The individual may experience mild discomfort or more severe limitations pertaining to muscle function. Generally, these conditions affect the physical capabilities of the individual due to the direct impact on skeletal muscles, which are responsible for overall body movement. Each precise condition under M63.8 will have specific manifestations, all of which present a divergence from normal muscle health and function.