Septic arthritis and rheumatic fever Flashcards
Differential diagnosis
- Hot stolen knee joints in child with fever
septic arthritis
Rheumatic fever
- other reactive arthritis
- Trauma (fracture, muscle injury)
Gram positive cocci
Streptococci - in chains or diplococci
–> causes beta haemolysis (complete break down of red cells in blood agar around colonies leaving it transparent)
(alpha haematology S.pneumoniae, Beta haematology Group A strep (strep pyogenes)
Staphylococci in clumps or clusters
- Coagulase positive s.aureus
Gram negative cocci
Neisseria meningitides
Neisseria gonococcus
Gram positive bacillus
Clostridium species
Listeria monocytogenes
Gram negative bacillus
Haemophillus influenzae
Enteric pathogens
E.coli, Shigella, Salmonella
What does strep have that helps it achieve beta haemolysis
Streptolysis
hyalouronidase
streptokinase
timbre protruding through capsule - important for adherence to epithelial cells; have M proteins associated
Important active extracellular products ‘toxins’ and antigens
Examples of group A streptococcal disease nonsuppurative “inflammatory” delayed sequelae which follow uncomplicated infections
Acute rheumatic fever
Rheumatic heart disease
Post streptococcal glomerulonephritis
Septic arthritis - complication of group A strep
Presence of infection from bacteria in bone and marrow and or joint space
occurs most commonly in childhood (<10years)
General systemic symptoms include fever and malaise
Swelling, erythema and tenderness around the affected joint
Clinically held in position that maximises intracapsular volume (flexed knee, flexed abducted externally rotated hip)
Arthritis definition
= limitation of movement, hot joint and pain or tender to palpate
Diagnostic procedures
knee joint easily examined and palpated (versus hp joint)
But plain X rays still useful particularly in paediatrics, help to rule out other causes like fracture, congenital and growth abnormalities (slipped femoral epiphyses and perthes)
Why are children more susceptible to bone and joint infections?
growing bone is highly vascular, theres lots of cartilage
growth plate
Treatment for infected joint?
2 joint washouts over consecutive days
IV antibiotics for 3 weeks
Then oral amoxycillin for 1 week
Key points about septic arthritis?
Needs to be diagnosed quickly as early treatment prevents complications such as irreversible damage from growth plate disruption
Early diagnosis can be difficult e.g. clinical presentation in young child (refusal to walk without localising pain
Lower extremities: knee, hip and ankle most commonly affected
Common bacterial causes are staphylococcus aureus and streptococcus pyogenes
Drainage and washout is often needed for both diagnosis (joint fluid culture) and treatment
IV antibiotics are needed initially and total course of antibiotics likely to be long (>2-3 weeks)
Rheumatic fever
differential diagnosis for NZ n
Autoimmune réponse following throat infection (pharyngitis) with Strep pyogenes
Generalised inflammation: attacking certain parts of the body - heart, joints, skin and/or brain
Can lead to lasting damage to mitral and/or aortic valves = rheumatic heart disease (RHD)
RHD the most common form of childhood heart disease in the world (developing countries and NZ)
Rheumatic fever diagnosis via the Jones criteria
Major criteria: Carditis (inflame of heart valves) Polyarthritis Sydenhams chorea Erythema marginatum (rare rash) Subcutaneous nodes (very rare)
Minor criteria: Fever Polyarthralgia History of rheumatic fever Raised acute phase reactants Prolonged PR interval on ECG
Aute rhematic fever diagnosis based on clustering of evidence plus: evidence of a preceding streptococcal infection
- rising ir elevated strep antibody titires OR
- Positive group A streptococcus throat culture
Arthralgia
joint pain, but without the heat and redness of an arthritis
Arthritis in rheumatic fever
commonest presenting symptom of acute rheumatic fever - up to 75% of first attacks
Typically arthritis of the ARF is extremely painful unable to weight bear
Large joints are usually affected, especially knees and ankles
Polyarthritis, usually asymmetrical and migratory (one becoming inflamed as another subsides)
Erythema marginatum
characteristic skin rash but uncommon <10% of first attacks of ARF
Can be difficult to see in dark skinned
Found on trunk, upper arms, legs and NOT face
Spread outwards in a circular shape, edge becomes raised, red and centre clears
Can persist intermittently for weeks to months, no other symptoms and often not noticed by patient
Rheumatic fever: molecular mimicry
normal host response to group A strep - produce antibodies to bacterial antigens
Production of cross reactive antibodies gives immune recognition and response against pathogen but produce antibodies which recognise both host and microbial antigens
e.g. human cardiac myosin and strep M protein are like important antigens in the pathogeneses of rheumatic heart disease
Why is preventing recurrent attacks crucially important?
Recurrent rheumatic fever attacks due to repeated strep infections lead to increased scar formation in the valve
After the initial attack of ARF and carditis the valve scars and then is neovascularised which perpetuates disease
Why are strep antibody titres a important part of confirming diagnosis?
most acute rheumatic fevers do not have culturepositigve throat (often no history of a sore throat either)
Even when group A strep cultured could represent carriage - docent confirm recent infection
Tests used are plasma antistreptolysin O (ASO) and the antideoxyribonuclease B (anti-DNase B) titres
ASO titre level is highest about 3-6 weeks after infection (about when children present with ARF)
Can take two months to decline and 6 months back to normal
Rheumatic fever treatment
Bed rested in hospital: 2 weeks
Monitor systemic inflammation (weekly ESR, CRP)
Family members throat swabbed and treated (public health)
Education about ARF and throat sores
Penicillin intramuscular injections every 4 weeks for the next 10 years
How are we preventing recurrences?
streptococcus pyogenes remains exquisitely susceptible to penicillin
Formulations of penicillin
- aqueous
Aqueous (water soluble) penicillin G (intravenous)
- Very high peak rapidly (15-30mins) but excreted rapidly within 2-4 hours
- Used for treating acute severe infections in places like meningitis, blood stream, pneumonia, septic arthritis
Formations of penicillin
Benzathine pen G (intramuscular injection)
low conc of serum penicillin G (only 1-2% the peak that aqueous gives BUT detectable amounts in serum >3 weeks
Pain at injection site a problem
Benzathine is appropriate for highly sensitive bacteria in highly vascular areas as diffuses readily
For treatment of group A strep in impetigo and for prophylaxis of strep sore throat in rheumatic fever
Oral penicillin
phenoxymathylpenicillin ‘penicillin V’
Absorbed well from GI tract - about 40% of same dose given as aqueous Ben pen G - good for mild to moderate infections
All penicillins excreted by both GFR and tubular secretion
Septic arthritis vs rheumatic fever
SA
- any age group (peak <10yrs)
- Acute active infection- arthritis due to bacteria and pus in joint - pyogenic bacteria
- Treatment with cleaning joint and penicillin to clear infection
RF
- School age 5-15
- anutimmune antibody response to S. pyogenes
- Multisystem inflammatory disease
Penicillin used long term to prevent recurrence
