Septic arthritis and rheumatic fever

Question 1

Septic arthritis

Answer 1

1. Presence of infection from bacteria in bone and marrow and/or joint space
2. Septic arthritis occurs most frequently in childhood (typically <10 years)
3. General systemic symptoms include fever and malaise (unwellness)
4. Swelling, erythema and tenderness around the affected joint.
5. Clinically joint held in position that maximises intracapsular volume (flexed knee, flexed abducted, ext-rotated hip).

Question 2

Common bacteria in bone and joint infection

Answer 2

1. staph aureus

2. strep pyogenes

Question 3

Treatment for septic arthitis

Answer 3

1. Joint washouts (also needed for diagnosis)
2. IV antibiotics 3 weeks
3. Oral penicillin 1 week

Question 4

Acute rheumatic fever

Answer 4

1.Auto-immune response following throat infection
(pharyngitis) with Streptococcus pyogenes
2. Throat infection with Grp A strep then latent period
of several weeks before symptoms of ARF begin
3. Generalised inflammation; attacking certain parts of the body – heart, joints, skin and/or brain
4. Can cause lasting damage to mitral and/or aortic valves = rheumatic heart disease (RHD)
5. RHD is the most common form of childhood heart disease in the world (developing countries & NZ)

Question 5

Jones criteria

Answer 5

2 major or 1 major and 2 minor

Major criteria
Carditis
Polyarthritis Sydenhams chorea Erythema marginatum Subcutaneousnodules

Minor criteria
Fever
Polyarthralgia (more than one joint in pain)
History of rheumatic fever
Raised acute phase reactants (C-reactive protein (CRP), erythrocyte sedimentation rates (ESR)
Prolonged PR interval on ECG

Question 6

Pathophysiology of ARF

Answer 6

1. Normal host response to group A streptococcus – produce antibodies to bacterial antigens
2. Production of cross-reactive antibodies gives immune recognition and response against pathogen – but produce antibodies which recognise both host and microbial antigens. –> human cardiac myosin and streptococcal M protein
3. Antibodies cross react with collagen or cardiac valvular endothelia antigens then Tcells infiltrate leading to inflammation (arthritis) or long term damage (carditis then RHD)
   4, Auto antibody-mediated neuronal cell signaling in cerebrospinal fluid may be part of pathogenesis in chorea
4. Recurrent rheumatic fever attacks due to repeated strep infections lead to increased scar formation in the valve.
5. After the initial attack of ARF and carditis, the valve scars and then is neovascularized (new vessels) which perpetuates disease

Question 7

ARF diagnosis

Answer 7

1. Antibody titres: plasma antistreptolysinO(ASO) (highest 2-6 weeks after infection) and the antideoxyribonuclease B (anti-DNase B) titres (6-11 weeks)
2. throat swab (not specific)

*2-4 fold increase or decrease n titred performed 14-21 days apart is indicative of recent infection

Question 8

Treatment of ARF

Answer 8

1. Bed rest (2 weeks)
2. Monitor systemic inflammation (weekly ESR, CRP)
3. Family members throat swabbed and treated (Public health)
4. Education about ARF and sore throats
5. Penicillin intramuscular injections every 4 weeks for next 10 years

• Strep pyogenes susceptible to penicillin but staph aureus produces betalactamase thus resistant –> requires flucloxacillin

Question 9

Penicillin

Answer 9

V: oral
G: IV

Aqueous(watersoluble)penicillinG(intravenous)
– Very high peak rapidly (15-30 mins) BUT excreted rapidly within 2-4 hrs
– Used for treating acute severe infections in places like meningitis, blood stream, pneumonia, SEPTIC ARTHRITIS

BenzathinepenG((intramuscularinjection)
– Low concentration of serum penicillin G (only 1-2% of peak that
aqueous gives) BUT detectable amounts in serum > 3 weeks
– Pain at injection site is problem (‘buzzy bee’, lignocaine)
– Benzathine is appropriate for highly sensitive bacteria in highly vascular areas as diffuses readily
– Used for treatment of grp A strep in impetigo and for prophylaxis of strep sore throat in rheumatic fever

Oral penicillin
– Phenoxymethylpenicillin ‘Penicillin V’
– Absorbed well from GI tract – about 40% of same dose given as aqueous Ben pen G – so are good for mild – mod infections (acute pharyngitis)

Question 10

Route of excretion for penicillin

Answer 10

GFR and tubular secretion

Question 11

Differences between the SA and ARF

Answer 11

SA
Any age group–infancy through to adulthood
• Acute active infection- arthritis due to bacteria and pus in the joint – pyogenic bacteria (S.aureus and S.pyogenes)
• Treatment with cleaning joint and penicillin to clear infection

ARF
School age 5–15 year
• Auto immune antibody
response to S.pyogenes
• Multi system inflammatory disease (symptoms and
signs of heart, joint, skin, brain involvement)
• Penicillin used long term to prevent recurrence (secondary prevention)