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Infectious disease and microbiology – Myositis
Myositis is an inflammatory condition of skeletal muscles that may arise from infectious causes—including bacteria, viruses, fungi, parasites, and mycobacteria—or from noninfectious conditions. A specific form, pyomyositis, refers to a hematogenous bacterial infection of muscle that frequently leads to abscess formation, whereas acute bacterial myositis involves diffuse muscle infection without abscess. The epidemiology varies depending on the causative organism, but pyomyositis is relatively rare in temperate regions and more common in tropical areas, where it may account for a notable proportion of hospital admissions. Risk factors include immunocompromised states such as HIV infection, chronic illnesses like diabetes and malignancy, alcoholism, trauma, surgery, obesity, and residence in tropical climates.
The pathophysiology often involves muscle injury or trauma, which may create a susceptible environment for infection due to local infarction or hemorrhage. A wide range of pathogens can cause myositis: viral agents such as influenza, HIV, and herpes viruses; parasitic organisms like Trichinella spiralis, Toxoplasma gondii, and Echinococcus; and bacterial pathogens, most notably Staphylococcus aureus, which accounts for the majority of pyomyositis cases. Other bacterial causes include streptococci, clostridia (leading to gas gangrene), and mixed aerobic and anaerobic organisms. Fungal infections and infections related to aquatic exposure (e.g., Aeromonas hydrophila, Vibrio vulnificus) are less common but clinically important.
Clinically, myositis often presents insidiously with localized muscle pain and fever, progressing to swelling, induration, and marked tenderness. Deep muscle infections may lack overlying skin changes, making diagnosis challenging. In advanced cases, findings such as crepitus, malodorous discharge, hemorrhagic bullae, or systemic signs of sepsis may appear. Laboratory evaluation typically shows leukocytosis and elevated muscle enzymes, while cultures from deep tissue or aspirated material are essential for identifying the causative organism. Imaging studies such as CT or MRI help determine the extent of muscle involvement and detect abscess formation, while ultrasound can assist in emergency settings.
Management usually requires a combined medical and surgical approach, particularly for bacterial myositis. Abscesses should be drained, and empiric antibiotic therapy should cover common pathogens such as S. aureus, with adjustments based on culture results. Severe infections, such as those caused by streptococci or clostridia, require urgent surgical debridement and high-dose antibiotics, often including penicillin and clindamycin. Treatment of parasitic infections depends on the specific organism, while viral myositis is generally managed supportively. Additional therapies, such as hyperbaric oxygen for clostridial infections or immunoglobulin in toxic shock, may be indicated in selected cases.
Patients often require hospitalization, especially in bacterial or severe parasitic cases, with close monitoring and supportive care. Despite treatment, prognosis can be serious in severe infections, particularly those caused by streptococci or clostridia, which carry high mortality rates. Potential complications include bacteremia, septic shock, limb necrosis, toxic shock syndrome, and death, underscoring the importance of early recognition and aggressive management.
Myositis is an inflammatory condition of skeletal muscles that may arise from infectious causes—including bacteria, viruses, fungi, parasites, and mycobacteria—or from noninfectious conditions. A specific form, pyomyositis, refers to a hematogenous bacterial infection of muscle that frequently leads to abscess formation, whereas acute bacterial myositis involves diffuse muscle infection without abscess. The epidemiology varies depending on the causative organism, but pyomyositis is relatively rare in temperate regions and more common in tropical areas, where it may account for a notable proportion of hospital admissions. Risk factors include immunocompromised states such as HIV infection, chronic illnesses like diabetes and malignancy, alcoholism, trauma, surgery, obesity, and residence in tropical climates.
The pathophysiology often involves muscle injury or trauma, which may create a susceptible environment for infection due to local infarction or hemorrhage. A wide range of pathogens can cause myositis: viral agents such as influenza, HIV, and herpes viruses; parasitic organisms like Trichinella spiralis, Toxoplasma gondii, and Echinococcus; and bacterial pathogens, most notably Staphylococcus aureus, which accounts for the majority of pyomyositis cases. Other bacterial causes include streptococci, clostridia (leading to gas gangrene), and mixed aerobic and anaerobic organisms. Fungal infections and infections related to aquatic exposure (e.g., Aeromonas hydrophila, Vibrio vulnificus) are less common but clinically important.
Clinically, myositis often presents insidiously with localized muscle pain and fever, progressing to swelling, induration, and marked tenderness. Deep muscle infections may lack overlying skin changes, making diagnosis challenging. In advanced cases, findings such as crepitus, malodorous discharge, hemorrhagic bullae, or systemic signs of sepsis may appear. Laboratory evaluation typically shows leukocytosis and elevated muscle enzymes, while cultures from deep tissue or aspirated material are essential for identifying the causative organism. Imaging studies such as CT or MRI help determine the extent of muscle involvement and detect abscess formation, while ultrasound can assist in emergency settings.
Management usually requires a combined medical and surgical approach, particularly for bacterial myositis. Abscesses should be drained, and empiric antibiotic therapy should cover common pathogens such as S. aureus, with adjustments based on culture results. Severe infections, such as those caused by streptococci or clostridia, require urgent surgical debridement and high-dose antibiotics, often including penicillin and clindamycin. Treatment of parasitic infections depends on the specific organism, while viral myositis is generally managed supportively. Additional therapies, such as hyperbaric oxygen for clostridial infections or immunoglobulin in toxic shock, may be indicated in selected cases.
Patients often require hospitalization, especially in bacterial or severe parasitic cases, with close monitoring and supportive care. Despite treatment, prognosis can be serious in severe infections, particularly those caused by streptococci or clostridia, which carry high mortality rates. Potential complications include bacteremia, septic shock, limb necrosis, toxic shock syndrome, and death, underscoring the importance of early recognition and aggressive management.
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