Mechanisms of muscle pain in long COVID

Medical News: As the world continues to adapt to the long-term effects of COVID-19, researchers are now turning their attention to the lingering symptoms experienced by many who have recovered from the virus. One particularly troubling symptom is myalgia, or skeletal muscle pain, which has been reported by many individuals suffering from what is now known as "long COVID." A recent study highlights new insights into the mechanisms behind muscle pain associated with long COVID, shedding light on the biological and clinical factors that contribute to this condition. This Medical News report explores the findings of that study and their implications for treatment and rehabilitation. The research comes from experts at Shanghai Jiaotong University, Shanghai Normal University Tianhua College, and Shanghai Sanda University in China.

Common locations of skeletal muscle pain in long COVID. Common locations of chronic skeletal muscle pain include the spine, shoulders, and limbs. Spinal pain is more common, with the highest incidence of skeletal muscle pain occurring in the lumbar muscles of the spine.

Persistent Muscle Pain: A Common Long COVID Symptom
Myalgia, or skeletal muscle pain, has emerged as one of the most persistent symptoms experienced by individuals recovering from COVID-19. Studies indicate that up to 65% of COVID-19 patients report muscle pain during their infection, with many continuing to suffer from pain weeks, months, or even a year after their initial recovery. This persistent pain has had a significant impact on patients’ quality of life, hindering their ability to resume normal activities and delaying their full recovery.
 
In some cases, this muscle pain is related to pre-existing conditions, such as musculoskeletal pain, which may be exacerbated by the viral infection. However, researchers have also discovered that even those with no prior history of muscle issues are experiencing severe discomfort following their COVID-19 infection. This has led scientists to explore the underlying mechanisms that might explain why muscle pain is so prevalent in long COVID cases.
 
The Mechanisms Behind Long COVID Muscle Pain
The study identifies several key factors contributing to muscle pain in long COVID patients, pointing to the role of inflammation, myopathy (muscle disease), and neurological damage. The virus is known to trigger an immune response, which can result in widespread inflammation throughout the body, including the skeletal muscles. This inflammatory response may lead to muscle damage, contributing to the prolonged pain experienced by long COVID patients.
 
Additionally, researchers have found evidence of mitochondrial dysfunction in individuals with long COVID. Mitochondria, often referred to as the "powerhouses" of cells, play a critical role in muscle function by producing the energy required for muscle contractions. Damage to mitochondria can result in oxidative stress, a condition in which harmful molecules accumulate and cause further damage to the muscle tissue.
 
The study also discusses how SARS-CoV-2, the virus responsible for COVID-19, may directly impact muscle cells. It is believed that the virus can enter muscle cells through angiotensin-converting enzyme 2 (ACE2) receptors, which are present in various tissues, including skeletal muscle. Once inside, the virus may cause cell damage either through direct infection or by triggering an excessive immune response, further contributing to muscle pain and fatigue.
 
Inflammation: A Major Culprit
One of the most significant findings of the study is the role of inflammation in muscle pain associated with long COVID. Inflammatory cytokines, such as interleukin-6 (IL-6), are elevated in patients with long COVID, and these molecules are known to cause pain and discomfort by activating pain receptors in the muscles. In severe cases, this inflammatory response can lead to a condition known as myositis, where the muscles become inflamed, swollen, and painful.

The study highlights that reducing inflammation is key to alleviating muscle pain in long COVID patients. Treatments targeting the immune system, such as corticosteroids, have been shown to reduce pain and improve muscle function. However, more research is needed to fully understand the best ways to manage inflammation in these patients.
 
Myopathy and Neurological Damage
In addition to inflammation, researchers have found that some long COVID patients develop myopathy, a disease that affects muscle fibers. Myopathy may be caused by direct viral infection of muscle cells or by an autoimmune response triggered by the virus. In cases where patients exhibit signs of myopathy, muscle biopsies have revealed damage to the muscle fibers, including necrosis (cell death) and fibrosis (scarring).
 
Neurological damage may also play a role in long COVID muscle pain. The nervous system controls muscle function, and damage to the nerves that communicate with muscles can lead to pain, weakness, and fatigue. This may explain why some patients continue to experience muscle pain long after their infection has resolved.
 
The Impact of Mitochondrial Dysfunction
Another critical factor contributing to muscle pain in long COVID patients is mitochondrial dysfunction. Mitochondria are essential for producing the energy required for muscle contractions, and damage to these organelles can result in muscle weakness and pain. The study found that patients with long COVID often exhibit signs of mitochondrial stress, which may be linked to reduced oxygen supply and inflammation caused by the virus.
 
Researchers have suggested that mitochondrial-targeted therapies, such as supplements to boost mitochondrial function, may help alleviate muscle pain in long COVID patients. However, further studies are required to determine the effectiveness of these treatments.
 
Treatment and Rehabilitation Approaches
The findings of this study suggest that a multidisciplinary approach is necessary to manage muscle pain in long COVID patients. In addition to medications that target inflammation, rehabilitation therapies, such as physical therapy and strength training, may help patients regain muscle function and reduce pain. The study emphasizes the importance of early intervention, as delayed treatment may result in prolonged recovery and worsening of symptoms.
 
Nutraceuticals, including supplements like vitamin D, zinc, and creatine, have also been proposed as potential treatments for muscle pain in long COVID patients. These supplements may help reduce inflammation, support mitochondrial function, and improve overall muscle health.
 
In some cases, interventional therapies, such as trigger point injections or dry needling, have been used to provide short-term relief for muscle pain. While these treatments can be effective in some patients, more research is needed to determine their long-term efficacy.
 
Conclusion: Moving Forward in Long COVID Research
As researchers continue to investigate the lingering effects of COVID-19, it is becoming clear that muscle pain is a significant concern for many long COVID patients. This study provides valuable insights into the mechanisms behind this condition, highlighting the roles of inflammation, myopathy, neurological damage, and mitochondrial dysfunction.
 
Moving forward, it is crucial that healthcare providers adopt a comprehensive approach to managing muscle pain in long COVID patients. This includes not only treating the underlying causes of pain but also providing rehabilitation and support to help patients recover their strength and mobility. As our understanding of long COVID continues to evolve, so too will our ability to provide effective treatments and improve the quality of life for those affected by this condition.
 
The study findings were published in the peer-reviewed American Journal of Clinical and Experimental Immunology.
https://e-century.us/files/ajcei/13/4/ajcei0155121.pdf
 
https://pubmed.ncbi.nlm.nih.gov/39310121/
 
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