|Myalgia refers to muscle pain. The pain may be localized, as in a muscle strain or crush injury, or generalized pain caused by an underlying disease such as a viral infection. The most common type of localized muscle pain is caused by muscle overuse or injury from strenuous activity.|
Myositis refers to muscle inflammation. Myositis can lead to muscle pain, swelling, and weakness. Temporary myositis may be caused by overexercise or injury to the muscles, and chronic forms can develop from viral and bacterial infections, medications, certain diseases, and autoimmune disorders. Both myalgia and myositis are symptoms of underlying conditions. Effective relief of myalgia and myositis requires diagnosis and treatment of the underlying condition causing these symptoms.
Diseases that may cause myalgia or myositis include viruses such as HIV, influenza, Epstein-Barr, herpes simplex, or poliomyelitis (Enterovirus), and connective tissue diseases (collagen vascular diseases), including autoimmune disorders such as rheumatoid arthritis, systemic lupus erythematosus, dermatomyositis, fibromyalgia, and polymyalgia. Myalgia may be associated with the involuntary muscle movement (spasticity) of central nervous system disorders such as multiple sclerosis, amyotrophic lateral sclerosis (ALS), and spinal cord injuries. Muscle pain also can accompany the rigidity associated with Parkinson's disease and myofascial pain syndrome.
Bacterial infections such as strep throat (Streptococcus), Lyme disease, and tetanus may be accompanied by myalgia or myositis. Fungi that cause histoplasmosis and parasites associated with malaria, toxoplasmosis, and trichinosis also can create symptoms that include myalgia and myositis. Muscle pain and inflammation may result from reactions to vaccinations (immunizations) or medications (e.g., anticonvulsants, antibiotics, anticancer agents, cholesterol-lowering agents, diuretics); abuse of substances such as alcohol, amphetamines, cocaine, or narcotics; poisons such as strychnine and snake, insect, or spider bites; and exposure to toxic chemicals and environmental factors such as ultraviolet light. Deficiencies in B-complex vitamins and vitamin C, mineral deficiencies, and electrolyte imbalances involving calcium, magnesium, phosphorus, potassium, or sodium, can cause myalgia. The condition also can result from certain endocrine and metabolic disorders such as hypothyroidism, hyperthyroidism, Addison's disease, hypoparathyroidism, diabetes mellitus, metastatic neoplasm, and diabetic neuropathy. Eosinophilia-myalgia with accompanying severe or chronic muscle pain can be an acute reaction to the ingestion of a contaminated dietary supplement known as L-tryptophan.
Other conditions in which myalgia and/or myositis may be present include sarcoidosis, compartment syndrome, certain inherited metabolic disorders, and muscle pain with no apparent physical basis (psychogenic myalgia). Individuals diagnosed with myositis may have underlying conditions such as pneumonia or other lung diseases.
Incidence and Prevalence: Since myalgia and myositis are symptoms rather than disorders, their specific incidence is unknown.