Inflammation of the muscles is known as myositis.1 The cause of myositis is many prominent being the infections. Infections include viral, bacterial and parasitic infections. The virus causes myositis through the various mechanism of actions. Myositis damages the molecular structure of the muscles and muscle fibers. The symptoms of myositis include weakness, pain, and stiffness of the muscles.
Can A Virus Attack Your Muscles?
Attack by the virus on the muscles and causing inflammation is known as viral myositis.2 Viral myositis results in the damage to muscle fibers and loss or alteration in the physiological function of muscles.
The symptoms experienced by the patient suffering from viral myositis include muscle weakness, tenderness, and pain due to stiff muscles. Although common in all age groups, the virus commonly attacks children probably due to the immature muscle cells. Prevalence of the disease is more in males as compared to females.
During the viral myositis, serum creatine kinase is elevated and the muscle biopsy reveals degeneration of muscle fibers with the leukocyte infiltration and muscle necrosis.
Viral myositis may be subacute, acute or chronic. While acute and sub-acute myositis is generally self-limiting and the condition subsides within a few days, chronic form of the disease requires medications and is the result of chronic viral infection which has progressed to muscles. Some cases of viral myositis may cause rhabdomyolysis.
The virus affects the muscles to cause myositis mainly through two different mechanisms:
Direct Infection. In these cases, the virus directly affects the muscles resulting in disruption of the muscular structure.
Inflammation. Whenever any foreign particles such as virus enter the body, it triggers the immune system. The immune system releases inflammatory mediators in response to the virus or other foreign particles. The inflammation may reach to the muscles causing myopathy.
Other mechanisms through which a virus causes myositis includes molecular mimicry, and persistent infections.
It has also been seen that the treatment of patients through antiretroviral drug may also result in myositis; Antiretroviral drugs such as Zidovudine functions by inhibiting the viral DNA polymerase and helps in managing HIV infection. However, during the process, these drugs also inhibit various critical enzymes of the human cells such as DNA polymerase beta and mitochondrial DNA polymerase gamma. This results in the inhibition of human mitochondrial DNA replication leading to a reduction in oxidative phosphorylation. Disturbance in oxidative phosphorylation results in the formation of active oxygen species and increased oxidative stress. This results in reduced energy production in muscles leading to muscle pain and weakness in muscles.
Calf muscle pain is most common in children recovering from a viral illness. The condition was termed as myalgia cruris epidemics by Lundeberg in 1957. The Benign Acute Childhood myositis is a non-serious self-limiting condition for which no specific treatment such as antiviral therapy is required.
The virus which has the potential to cause myositis includes Cytomegalovirus, Epstein Barr Virus, adenovirus, influenza A and B, parainfluenza, herpes simplex, and Coxsackie. The viral myositis has natural recovery and does not require any treatment however in some cases life-threatening complications such as acute renal failure, cardiac arrhythmia, rhabdomyolysis, myoglobinuria, and compartment syndrome may lead to significant morbidity. Among the myositis causing virus, most cases are caused by influenza A and Influenza B virus. Studies indicate that influenza B is more potent in causing myositis as compared to influenza A virus. This is due to the fact that influenza B virus has a unique NB protein present in its membrane that helps in viral entry and is all related to myotrophic properties.
Viral myositis is caused either through the direct attack of the virus on muscles or the immune system causes inflammation of the muscles. Viral culture from the muscles is unsuccessful however; the increased level of creatinine kinase indicates muscle degeneration. Although the condition is self-limiting and does not require any treatment however, some cases of myositis progress to develop rhabdomyolysis, renal failure or cardiac arrhythmia.
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