Before the Covid-19 pandemic, we were used to annual flu waves, with news showing hospital corridors packed with people suffering from the worst flu symptoms, including pneumonia.
Fortunately, for most patients, flu symptoms are benign and do not require hospitalization. The most common of these symptoms is fever, which leads to chills and cold sweats, headache, persistent or dry cough with sore throat, stuffy nose, weakness and… terrible muscle and joint pain. If influenza viruses like Covid-19 enter our bodies through the respiratory tract, affecting the mucous membranes of the nose, throat and lungs, why?
Immune response is a double-edged sword
In most respiratory viral infections, symptoms are not caused directly by the action of the virus but by the immune system’s response to eliminate the virus. Sore throat, cough, increased mucus, and fever are just symptoms of the body’s response to the immune system. That’s why they are a common cause of countless viral and bacterial illnesses.
In general, almost any disease that produces inflammation will eventually cause these common symptoms, including muscle weakness, aches, and joint pain. Regardless of the pathogen causing these symptoms, they are caused by an inflammatory response. Muscle inflammation accompanied by weakness is called myositis, and myalgia is the name for muscle and joint pain.
When an immune response against a pathogen occurs, the different cells involved release a series of small proteins called cytokines. Cytokines come from different families and regulate a variety of activities in cells of the immune system and other organs. Some serve to signal the location of an infection, some regulate the type of response that must occur depending on the pathogen of the infection, some control the strength of the immune response, and some even regulate the repair of damage to organs and fabrics.
Cytokines are part of a complex signaling system that cells of the immune system need to control immune responses, but can also affect other tissues and organs. Many cytokines produce inflammation not only at the site of infection but also in other organs, including muscles and muscles.
joint. Therefore, in influenza and other respiratory infections, including covid-19, muscle pain occurs that is very similar to what is experienced with mild arthritis.
Among these cytokines, interleukin 1-beta (IL-1b) produces fever, interleukins 6 (IL-6) and 17 (IL-17), and tumor necrosis factor-alpha (TNF-a), Most relevant to explain muscle pain. In case of influenza and other viral infections, High levels of IL-6 in muscles linked to pain.
This pain may be related to Muscle loss due to influenza But it is also related to other things that can produce Muscle fiber rupture or rhabdomyolysis. These muscle tears are associated with high levels of IL-6 or TNF-a following infection.
In response to these cytokines, muscles produce elevated levels of prostaglandin E.2 (prostaglandin E2), Lipid molecules linked to inflammation and pain. Therefore, NSAIDs are used to relieve pain and muscle weakness, and their mechanism of action is to inhibit the production of PGE.2. Such as ibuprofen or paracetamol.
Pain relief, yes or no?
We just explained that muscle and joint pain are both side effects of the inflammatory response as the immune system tries to deal with an infection. Regardless of the cause of inflammation, the presence of inflammatory cytokines causes the most severe symptoms in muscles and joints. Symptoms include not only pain but also muscle fiber loss.
Now, there is a paradox. Inflammation is the first strategy the immune system uses when trying to deal with a viral infection. What’s more, the inflammatory response is critical for controlling infection and repairing damage caused by viruses and bacteria. If these responses are part of an array of weapons our bodies use in their ongoing battle against pathogens, does it make sense to eliminate them?
Muscle pain and weakness caused by a viral infection may be tolerable collateral damage. Another thing that’s very different is when they become chronic symptoms related to an immune system imbalance, it can lead to unexplained chronic muscle inflammation.
This may be what happens in other types of myalgia and fibromyalgia.although there is still a lot of discussion about it.Need to find key to affecting chronic muscle pain with weakness, Uncontrolled release of pro-inflammatory cytokines may be responsible. Therefore, controlling the levels of these cytokines is important in the treatment of such diseases.
Guillermo Lopez Luch
Professor in the field of cell biology. Associate Researcher at the Andalusian Center for Developmental Biology. Metabolism, aging, immune and antioxidant systems researcher. , Pablo de Olavide University