Overview
Definition:
Cellulitis is a bacterial infection of the dermis and subcutaneous tissue, typically presenting with erythema, warmth, swelling, and tenderness of the affected skin
Osteomyelitis is an infection of the bone, which can be hematogenous or direct, leading to inflammation, bone destruction, and potential abscess formation.
Epidemiology:
Both are common in children
Cellulitis is more frequent, often affecting the extremities
Osteomyelitis incidence is lower but carries higher morbidity
most cases occur in children under 10 years old, with a predilection for long bones
Staphylococcus aureus is the most common pathogen for both in this age group.
Clinical Significance:
Accurate differentiation is crucial for timely and appropriate management
Misdiagnosis can lead to delayed treatment, leading to significant complications such as chronic osteomyelitis, joint damage, limb deformities, sepsis, and even death
DNB and NEET SS examinations frequently test this differential diagnosis.
Clinical Presentation
Symptoms:
Cellulitis: Rapid onset of localized erythema, warmth, and swelling
Pain and tenderness over the affected area
Fever, malaise, and sometimes chills
Symptoms may spread rapidly
Osteomyelitis: Gradual onset of localized bone pain, often described as deep or throbbing
Limp or refusal to bear weight is common in lower extremity involvement
Fever, irritability, and malaise may be present
Symptoms may be less acute than cellulitis.
Signs:
Cellulitis: Well-demarcated or poorly demarcated erythematous, warm, swollen area of skin
May have blistering or purulent drainage
Lymphadenopathy may be present
Tenderness on palpation
Absence of deep warmth or joint effusion
Osteomyelitis: Localized tenderness directly over bone
Swelling may be present, but often deeper than cellulitis
Limited range of motion in adjacent joints
Pseudoparalysis may be seen in infants
Signs of sepsis (hypotension, tachycardia, altered mental status) can occur in severe cases.
Diagnostic Criteria:
No single criterion definitively differentiates
Diagnosis is often presumptive based on clinical presentation and supported by investigations
Fever >38.3°C (101°F) and localized signs of inflammation are key for both
Radiographic evidence of bone destruction or periosteal reaction (osteomyelitis) or absence thereof (cellulitis) is critical
Laboratory markers like elevated ESR and CRP are nonspecific but helpful.
Diagnostic Approach
History Taking:
Detailed history of onset and progression of symptoms
Trauma or recent injury to the affected limb
Skin breaks, insect bites, or wounds
History of recent infections (e.g., otitis media, sinusitis, urinary tract infections) for hematogenous spread
Recent antibiotic use
Underlying medical conditions (e.g., sickle cell disease, cystic fibrosis).
Physical Examination:
Systematic examination of the affected limb and adjacent joints
Differentiate superficial skin swelling from deeper bone tenderness
Assess for skin lesions, erythema, warmth, and edema
Palpate for localized bony tenderness
Assess range of motion of adjacent joints
Check for joint effusion or effusion
Evaluate for signs of systemic illness and sepsis.
Investigations:
Laboratory: Complete Blood Count (CBC) with differential (leukocytosis often present)
Erythrocyte Sedimentation Rate (ESR) and C-reactive protein (CRP) are elevated in both but higher in osteomyelitis
Blood cultures if sepsis is suspected
Imaging: X-ray is the initial imaging modality, but changes in osteomyelitis may not be apparent for 7-14 days (periosteal reaction, osteolysis)
Ultrasound can detect soft tissue edema and abscesses in cellulitis, and sometimes effusion
MRI is the gold standard for diagnosing osteomyelitis, detecting early bone edema, marrow changes, periosteal reaction, and abscesses
It also helps differentiate cellulitis from osteomyelitis
Radionuclide bone scans (e.g., technetium-99m) can detect increased bone activity but are less specific.
Differential Diagnosis:
Transient synovitis, septic arthritis, juvenile idiopathic arthritis, trauma (fracture, contusion), insect bites, deep vein thrombosis, sickle cell crisis, foreign body reaction, malignant bone tumors (Ewing sarcoma, osteosarcoma)
Differentiating from cellulitis: deeper pain, bony tenderness, limp, absence of clear skin lesion, elevated inflammatory markers disproportionately high for soft tissue involvement.
Management
Initial Management:
Pain and fever control with antipyretics (paracetamol, ibuprofen)
Immobilization of the affected limb
Elevation to reduce swelling
Prompt intravenous fluid resuscitation if dehydrated or septic.
Medical Management:
Antibiotics: For suspected cellulitis or osteomyelitis, empiric antibiotic therapy should be initiated promptly
In children without significant comorbidities, antistaphylococcal antibiotics like flucloxacillin or cefazolin are often first-line
If MRSA is suspected or prevalent in the community, vancomycin or clindamycin is indicated
For confirmed osteomyelitis, prolonged therapy (typically 4-6 weeks) is required, initially IV and then transitioning to oral based on clinical response and inflammatory markers
Blood cultures guide targeted therapy
Surgical drainage of any abscesses is crucial.
Surgical Management:
Surgical intervention is indicated for osteomyelitis with abscess formation, non-resolving infection despite antibiotics, or if debridement is required for dead bone or loose bodies
Needle aspiration or open biopsy for culture and sensitivity may be necessary for diagnosis and guiding antibiotic therapy in complicated cases.
Supportive Care:
Close monitoring of vital signs, pain levels, and limb function
Regular reassessment of the affected area
Physical therapy may be required to regain strength and mobility after resolution
Nutritional support
Education for parents regarding wound care, medication adherence, and warning signs of recurrence.
Complications
Early Complications:
Cellulitis: Bacteremia, sepsis, abscess formation, lymphangitis
Osteomyelitis: Septic arthritis if joint is involved, vertebral osteomyelitis leading to spinal cord compression, compartment syndrome.
Late Complications:
Cellulitis: Recurrent episodes, lymphedema
Osteomyelitis: Chronic osteomyelitis, pathological fractures, growth plate disturbance leading to limb length discrepancy or deformity, joint contractures, avascular necrosis.
Prevention Strategies:
Prompt treatment of skin breaks and wounds
Good hygiene
Management of predisposing conditions (e.g., eczema, fungal infections)
Prompt evaluation and treatment of suspected infections
Education regarding signs and symptoms of infection.
Prognosis
Factors Affecting Prognosis:
Timeliness of diagnosis and initiation of treatment
Virulence of the pathogen
Presence of comorbidities or immunocompromise
Development of complications like sepsis or abscess
Patient's age and overall health.
Outcomes:
With prompt and appropriate treatment, cellulitis generally resolves completely
Osteomyelitis prognosis is good if diagnosed and treated early, with most children recovering without long-term sequelae
However, delayed or inadequate treatment can lead to chronic osteomyelitis, requiring extensive management and potentially resulting in permanent disability.
Follow Up:
Regular clinical assessment and monitoring of inflammatory markers (ESR, CRP) are essential during and after treatment for osteomyelitis
Imaging may be repeated to assess healing
Long-term follow-up may be necessary to monitor for growth disturbances or chronic infection.
Key Points
Exam Focus:
Differentiating mechanism (superficial vs
deep), common pathogens (Staph aureus), preferred imaging (MRI for osteomyelitis), antibiotic choices (IV for osteomyelitis, duration), and complications
DNB/NEET SS often present cases requiring precise differentiation based on subtle clinical clues and investigation findings.
Clinical Pearls:
Always examine the entire limb and adjacent joints
Deep bone tenderness is a hallmark of osteomyelitis
A normal X-ray does not rule out early osteomyelitis
consider MRI if suspicion is high
Early surgical drainage of abscesses is crucial in osteomyelitis management.
Common Mistakes:
Mistaking osteomyelitis for cellulitis due to superficial swelling
Delaying MRI in suspected osteomyelitis
Inadequate duration of antibiotic therapy for osteomyelitis
Failure to culture abscess material
Over-reliance on X-ray in early osteomyelitis.