Septic arthritis and rheumatic fever

Question 1

Differential diagnosis

- Hot stolen knee joints in child with fever

Answer 1

septic arthritis
Rheumatic fever
- other reactive arthritis
- Trauma (fracture, muscle injury)

Question 2

Gram positive cocci

Answer 2

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

Question 3

Gram negative cocci

Answer 3

Neisseria meningitides

Neisseria gonococcus

Question 4

Gram positive bacillus

Answer 4

Clostridium species

Listeria monocytogenes

Question 5

Gram negative bacillus

Answer 5

Haemophillus influenzae
Enteric pathogens
E.coli, Shigella, Salmonella

Question 6

What does strep have that helps it achieve beta haemolysis

Answer 6

Streptolysis
hyalouronidase
streptokinase
timbre protruding through capsule - important for adherence to epithelial cells; have M proteins associated
Important active extracellular products ‘toxins’ and antigens

Question 7

Examples of group A streptococcal disease nonsuppurative “inflammatory” delayed sequelae which follow uncomplicated infections

Answer 7

Acute rheumatic fever
Rheumatic heart disease
Post streptococcal glomerulonephritis

Question 8

Septic arthritis - complication of group A strep

Answer 8

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)

Question 9

Arthritis definition

Answer 9

= limitation of movement, hot joint and pain or tender to palpate

Question 10

Diagnostic procedures

Answer 10

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)

Question 11

Why are children more susceptible to bone and joint infections?

Answer 11

growing bone is highly vascular, theres lots of cartilage

growth plate

Question 12

Treatment for infected joint?

Answer 12

2 joint washouts over consecutive days
IV antibiotics for 3 weeks
Then oral amoxycillin for 1 week

Question 13

Key points about septic arthritis?

Answer 13

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)

Question 14

Rheumatic fever

Answer 14

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)

Question 15

Rheumatic fever diagnosis via the Jones criteria

Answer 15

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

1. rising ir elevated strep antibody titires OR
2. Positive group A streptococcus throat culture

Question 16

Arthralgia

Answer 16

joint pain, but without the heat and redness of an arthritis

Question 17

Arthritis in rheumatic fever

Answer 17

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)

Question 18

Erythema marginatum

Answer 18

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

Question 19

Rheumatic fever: molecular mimicry

Answer 19

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

Question 20

Why is preventing recurrent attacks crucially important?

Answer 20

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

Question 21

Why are strep antibody titres a important part of confirming diagnosis?

Answer 21

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

Question 22

Rheumatic fever treatment

Answer 22

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

Question 23

How are we preventing recurrences?

Answer 23

streptococcus pyogenes remains exquisitely susceptible to penicillin

Question 24

Formulations of penicillin

- aqueous

Answer 24

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

Question 25

Formations of penicillin

Answer 25

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

Question 26

Oral penicillin

Answer 26

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

Question 27

Septic arthritis vs rheumatic fever

Answer 27

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