L15: Septic arthritis and rheumatic fever Flashcards
Differentials - child with hot, swollen knee joint
Rheumatic fever:
- Migratory polyarthritis
- Often carditis
- Associated with group A strep infection
- School age 5-15yrs
Septic arthritis:
- Milk yellow/white purulent synovial fluid
- Extremely painful with movement
- From blood, nearly soft tissue infection, osteomyelitis
- Any age group (peak <10yrs)
+ other reactive arthritis, trauma
Group A streptococcus
- Beta haemolytic - complete break down of RBCs in blood agar)
- Cocci in chains
- Fimbrae that protrude through capsule
- Active extracellular products can cause toxic shock (or diagnose infection)
Typing:
- M typing using M proteins (emm typing)
- M protein resists phagocytosis
- Different M types with different clinical syndromes
- Antibodies against exotoxins to test if had strep in past
Group A strep - acute pyogenic/suppurative infections
Can be fulminant and life-threatening
- Tonsillitis/pharyngitis
- Skin (impetigo/cellulitis)
- Scarlet fever
- Bloodstream infection
- Septic arthritis
- Necrotising fasciitis
- Pneumonia/emphysema
- Myositis
- Toxic shock syndrome
- Puerperal sepsis
Group A strep - nonsuppurative “inflammatory” infections
Delayed sequelae following uncomplicated infections
Tonsillitis -> acute rheumatic fever (rheumatic heart disease)
Skin -> post streptococcal glomerulonephritis
Septic arthritis
= suppurative complication of group A strep
- Infection from bacteria in bone and BM (osteomyelitis) and/or joint space (septic arthritis)
- Septic arthritis occurs most freq in childhood <10yrs
- General systemic symptoms: fever, malaise
- Swelling, erythema (red) and tenderness around affected joint
- Joint held in position that maximises intracapsular volume (flexed knee, flexed abducted and externally rotated hip)
- Arthritis = limitation of movement, hot joint and pain or tender to palpate
Examination for septic arthritis
- Knee joint easily examined and palpated, hip harder
- Plain x-ray useful esp. for paeds
- Helps rule out other causes e.g. fracture, congenital and growth abnormalites
Why are children susceptible to bone and joint infections?
Growth plates unfused, high blood supply and bacteria e.g. group A strep enter areas where there is a high concentration of blood flow
Management of septic arthritis
- Joint washouts (remove pus from joint space for diagnosis and treatment)
- IV antibiotics (2-3wks)
- Then oral amoxycillin for 1wk
Key points about septic arthritis
- Diagnosis needs to be made quickly to prevent complications (e.g. irreversible damage from growth plate disruption, pus degrading cartilage, pus causing sepsis)
- Early diagnosis can be difficult (e.g. v young children)
- Often in weight-bearing lower limb (ankle, knee hip)
- Common bacterial causes: S. aureus and S. pyogenes
- Total course of antibiotics usually 2-3weeks
Acute rheumatic fever
- Autoimmune response following pharyngitis with strep pyogenes
- Generalised inflammation attacking heart, joints, skin, brain
- Can cause lasting damage to mitral and aortic valve = rheumatic heart disease
- RHD most common form of childhood heart disease
- Throat infection with group A strep (red, swollen, exudate on tonsils) then latent period for several weeks before symptoms of ARF
Jone’s criteria for ARF diagnosis
2 major or 1 major + 2 minor
AND evidence of preceding strep infection (rising antibodies, positive throat culture)
Major: Carditis (prolonged PR interval, regurg murmur), polyarthritis, Sydenham’s chorea, erythema marginatum (rare), subcutaneous nodules (v. rare)
Minor: fever, polyarthralgia, history of RF, raised acute phase reactants (ESR/CRP), prolonged PR interval
Arthritis in ARF
- Commonest presenting symptom
- Typically extremely painful, unable to bear weight
- Large joint usually affected (knee, ankle)
- Polyarthritis is asymmetrical, migratory
Sydenham’s chorea in ARF
- Dance-like
- Fidgeting
- Hypotonia
- Writhing hand movements
e. g. Chameleon tongue (darting when tries to poke out), cannot write, difficulty walking
RF - skin presentations
Erythema marginatum:
- Characteristic skin rash but uncommon <10% of first ARF attacks
- Trunk, upper arms and legs, not face
- Spreads outwards in circular shape, edge raised, red and centre clears
- Can persist intermittently for weeks-months
Subcutaneous nodules extremely uncommon
Mechanism of ARF
- Autoimmune mechanisms by molecular mimicry
- Normal host response to group strep -> produce antibodies to bacterial antigens
- Production of cross-reactive antibodies can recognise host and pathogens
- Attacks cardiac myosin, collagen of joints, heart valve endothelium
- Auto antibody-mediated neuronal signalling involved in chorea
