What are the causes of myalgia (muscle pain)?

From the Guidelines

Myalgia should be initially managed with rest, ice or heat application, and over-the-counter pain relievers like acetaminophen (500-1000mg every 6 hours, not exceeding 4000mg daily) or NSAIDs such as ibuprofen (400-600mg every 6-8 hours with food), as these approaches are supported by the most recent and highest quality evidence 1.

Causes and Mechanisms

Myalgia can be caused by various factors including overuse, injury, viral infections, medications, or underlying medical conditions. The pain can result from inflammation, micro-tears in muscle fibers, or biochemical changes within muscles that trigger pain signals. In some cases, myalgia may be part of a broader condition like fibromyalgia or an autoimmune disorder, which would require specialized treatment approaches beyond simple pain management.

Initial Management

For mild myalgia, the initial approach should include:

• Rest to avoid further strain on the affected muscles
• Applying ice or heat to the affected areas to reduce pain and inflammation
• Taking over-the-counter pain relievers like acetaminophen or NSAIDs such as ibuprofen
• Gentle stretching to maintain flexibility and reduce stiffness
• Staying hydrated to help the body recover from muscle strain

Persistent or Severe Myalgia

For persistent myalgia lasting more than a week, worsening pain, or pain accompanied by fever, rash, or weakness, a medical evaluation is necessary. These symptoms could indicate more serious conditions requiring specific treatment. It's also important to assess for predisposing factors for statin-associated muscle symptoms (SAMS) if the patient is on statin therapy, as myalgia can be a side effect of statin use 1.

Special Considerations

In cases where myalgia is suspected to be related to statin use, a thorough assessment of symptoms and evaluation for non-statin etiologies is recommended. The decision to continue or discontinue statin therapy should be made based on the individual patient's risk-benefit profile, considering the potential benefits of statin therapy on cardiovascular outcomes against the risk of muscle symptoms 1.

Alternative Treatments

For chronic pain conditions, including myalgia, alternative treatments such as physical therapy, exercise, stress management, and cognitive behavioral therapy may be beneficial. These approaches can help manage pain and improve quality of life without the need for pharmacological interventions 1.

From the FDA Drug Label

Musculoskeletal: Myalgia The cyclobenzaprine drug label reports myalgia as a rare adverse reaction, with a causal relationship that could not be established.

• Myalgia is listed under the category of "Causal Relationship Unknown" and "Musculoskeletal" adverse reactions.
• The incidence of myalgia is not specified in the drug label.
• The label does mention that cyclobenzaprine is used to relieve muscle spasm associated with acute, painful musculoskeletal conditions, but it does not provide information on the drug's effect on myalgia specifically 2.

From the Research

Definition and Prevalence of Myalgia

• Myalgia, also known as muscle pain or muscle ache, is a symptom associated with many diseases, including fibromyalgia, neurodegenerative diseases, and degenerative spine diseases 3.
• It is estimated that 60-85% of the population experiences myalgia at some point in their lifetime 3.
• Myalgia can be a major medical problem, and effective treatment for intractable myalgia, such as fibromyalgia, is still lacking 3.

Causes and Mechanisms of Myalgia

• One known source of muscle pain is tissue acidosis, which can activate chemosensitive nociceptors via proton-sensing ion channels and receptors 3.
• Acid signaling in muscle afferents can be either pro-nociceptive or antinociceptive, and recent studies have shown that proton-sensing ion channels and receptors are expressed in all subpopulations of somatosensory neurons 3.
• Oxidative stress can also trigger fibromyalgia-like pain in mice by activating proton-sensing ion channels 3.
• Myalgia can be a symptom of small and medium-sized vasculitis, such as anti-neutrophil cytoplasmic antibody-associated vasculitis (AAV) or polyarteritis nodosa (PAN) 4.

Diagnosis and Diagnostic Testing

• Diagnostic testing for myalgia may include muscle biopsy, electromyography, exercise and strength testing, and blood measurements, such as creatine kinase and erythrocyte sedimentation rate 5.
• Muscle magnetic resonance imaging can be useful in determining the biopsy site in patients with myalgia 4.
• Laboratory testing, including complete blood count, comprehensive metabolic panel, measurement of inflammatory markers and autoantibodies, and flow cytometry, can be valuable in evaluating patients with suspected autoimmune diseases, including those that may cause myalgia 6.
• Fibromyalgia diagnosis is typically made by a rheumatologist based on a history of widespread musculoskeletal pain and the presence of tender points 7.

Treatment and Management

• Conventional medical therapies for fibromyalgia and other conditions that cause myalgia often produce limited benefits and are largely pharmacological in nature 7.
• Many patients with fibromyalgia turn to complementary medicine to manage their symptoms, with 90% of patients using alternative therapies in addition to conventional treatments 7.
• Understanding the mechanisms of acid signaling in muscle afferents may provide novel therapeutic strategies for myalgia 3.