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Infectious disease and microbiology – Osteomyelitis
Osteomyelitis is an infection of bone, most commonly caused by bacteria and only rarely by fungi. It may present as acute disease, developing over days to weeks, or as chronic osteomyelitis, which evolves over months or years and is often associated with necrotic bone (sequestrum). The condition has an estimated incidence of 10–100 cases per 100,000 population and arises in a variety of clinical settings depending on host factors and route of infection.
Several risk factors predispose individuals to osteomyelitis, including diabetes mellitus (especially with foot ulcers), intravenous drug use, peripheral vascular disease, trauma, immunosuppression, and prior surgery or prosthetic implants. Certain organisms are associated with specific populations—for example, Salmonella in patients with sickle cell disease and Pseudomonas aeruginosa in intravenous drug users or puncture wounds through footwear. Preventive strategies emphasize good diabetic foot care and maintaining sterile surgical conditions, particularly for prosthetic procedures.
Infection reaches bone through three principal mechanisms: hematogenous spread, direct inoculation (trauma or surgery), or contiguous spread from nearby infected tissues. Once established, infection can involve the cortex, medullary cavity, and periosteum, leading to inflammation, abscess formation, and eventual bone necrosis. In children, infection commonly affects the metaphysis of long bones, whereas in adults, vertebral involvement is more typical.
The etiology is broad, with Staphylococcus aureus being the most common pathogen overall. Other causes include gram-negative organisms (e.g., Enterobacteriaceae), Pseudomonas, coagulase-negative staphylococci (especially in prosthetic infections), Mycobacterium tuberculosis, fungi such as Candida or endemic mycoses, and less commonly Brucella or organisms related to travel exposures.
Clinically, patients often present with localized bone pain, fever, swelling, and warmth over the affected area. Chronic cases may feature sinus tract formation with drainage. Recurrent or persistent cellulitis over a bony area should raise suspicion for underlying osteomyelitis. Diagnosis relies on a combination of laboratory testing and imaging, but the gold standard is bone biopsy for culture and histopathology, ideally obtained before antibiotic therapy. Blood cultures may identify the organism in up to 40% of acute cases, while inflammatory markers such as ESR are useful for monitoring disease activity.
Imaging plays a crucial role: plain X-rays may initially be normal, while MRI is highly sensitive, especially for spinal disease. CT scans can detect early cortical changes, and radionuclide scans are useful for early detection and identifying multifocal involvement. Advanced imaging such as PET may be helpful in chronic or unclear cases.
Management requires a combined medical and surgical approach. Prolonged antibiotic therapy (typically ≥6 weeks) is essential and should be tailored to the identified organism. For example, methicillin-susceptible S. aureus is treated with nafcillin or oxacillin, while MRSA requires vancomycin or alternative agents. Gram-negative infections are treated with fluoroquinolones or third-generation cephalosporins, and Pseudomonas infections require antipseudomonal agents. Importantly, surgical debridement of necrotic bone is often necessary, especially in chronic disease, and removal of infected prosthetic material may be required.
The prognosis is generally good for acute osteomyelitis with timely treatment but more guarded in chronic cases, where recurrence is common. Complications can be severe and include bone destruction, pathological fractures, epidural abscess with spinal cord compression, cranial neuropathies (in skull base involvement), amyloidosis, and even malignant transformation (Marjolin’s ulcer). Long-term follow-up is essential, as clinical and radiologic resolution may lag behind actual disease control.
Osteomyelitis is an infection of bone, most commonly caused by bacteria and only rarely by fungi. It may present as acute disease, developing over days to weeks, or as chronic osteomyelitis, which evolves over months or years and is often associated with necrotic bone (sequestrum). The condition has an estimated incidence of 10–100 cases per 100,000 population and arises in a variety of clinical settings depending on host factors and route of infection.
Several risk factors predispose individuals to osteomyelitis, including diabetes mellitus (especially with foot ulcers), intravenous drug use, peripheral vascular disease, trauma, immunosuppression, and prior surgery or prosthetic implants. Certain organisms are associated with specific populations—for example, Salmonella in patients with sickle cell disease and Pseudomonas aeruginosa in intravenous drug users or puncture wounds through footwear. Preventive strategies emphasize good diabetic foot care and maintaining sterile surgical conditions, particularly for prosthetic procedures.
Infection reaches bone through three principal mechanisms: hematogenous spread, direct inoculation (trauma or surgery), or contiguous spread from nearby infected tissues. Once established, infection can involve the cortex, medullary cavity, and periosteum, leading to inflammation, abscess formation, and eventual bone necrosis. In children, infection commonly affects the metaphysis of long bones, whereas in adults, vertebral involvement is more typical.
The etiology is broad, with Staphylococcus aureus being the most common pathogen overall. Other causes include gram-negative organisms (e.g., Enterobacteriaceae), Pseudomonas, coagulase-negative staphylococci (especially in prosthetic infections), Mycobacterium tuberculosis, fungi such as Candida or endemic mycoses, and less commonly Brucella or organisms related to travel exposures.
Clinically, patients often present with localized bone pain, fever, swelling, and warmth over the affected area. Chronic cases may feature sinus tract formation with drainage. Recurrent or persistent cellulitis over a bony area should raise suspicion for underlying osteomyelitis. Diagnosis relies on a combination of laboratory testing and imaging, but the gold standard is bone biopsy for culture and histopathology, ideally obtained before antibiotic therapy. Blood cultures may identify the organism in up to 40% of acute cases, while inflammatory markers such as ESR are useful for monitoring disease activity.
Imaging plays a crucial role: plain X-rays may initially be normal, while MRI is highly sensitive, especially for spinal disease. CT scans can detect early cortical changes, and radionuclide scans are useful for early detection and identifying multifocal involvement. Advanced imaging such as PET may be helpful in chronic or unclear cases.
Management requires a combined medical and surgical approach. Prolonged antibiotic therapy (typically ≥6 weeks) is essential and should be tailored to the identified organism. For example, methicillin-susceptible S. aureus is treated with nafcillin or oxacillin, while MRSA requires vancomycin or alternative agents. Gram-negative infections are treated with fluoroquinolones or third-generation cephalosporins, and Pseudomonas infections require antipseudomonal agents. Importantly, surgical debridement of necrotic bone is often necessary, especially in chronic disease, and removal of infected prosthetic material may be required.
The prognosis is generally good for acute osteomyelitis with timely treatment but more guarded in chronic cases, where recurrence is common. Complications can be severe and include bone destruction, pathological fractures, epidural abscess with spinal cord compression, cranial neuropathies (in skull base involvement), amyloidosis, and even malignant transformation (Marjolin’s ulcer). Long-term follow-up is essential, as clinical and radiologic resolution may lag behind actual disease control.
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