Septic arthritis and rheumatic fever Flashcards
Septic arthritis
- Presence of infection from bacteria in bone and marrow and/or joint space
- Septic arthritis occurs most frequently in childhood (typically <10 years)
- General systemic symptoms include fever and malaise (unwellness)
- Swelling, erythema and tenderness around the affected joint.
- Clinically joint held in position that maximises intracapsular volume (flexed knee, flexed abducted, ext-rotated hip).
Common bacteria in bone and joint infection
- staph aureus
2. strep pyogenes
Treatment for septic arthitis
- Joint washouts (also needed for diagnosis)
- IV antibiotics 3 weeks
- Oral penicillin 1 week
Acute rheumatic fever
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)
Jones criteria
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
Pathophysiology of ARF
- Normal host response to group A streptococcus – 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. –> human cardiac myosin and streptococcal M protein
- 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 - 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 neovascularized (new vessels) which perpetuates disease
ARF diagnosis
- Antibody titres: plasma antistreptolysinO(ASO) (highest 2-6 weeks after infection) and the antideoxyribonuclease B (anti-DNase B) titres (6-11 weeks)
- throat swab (not specific)
*2-4 fold increase or decrease n titred performed 14-21 days apart is indicative of recent infection
Treatment of ARF
- Bed rest (2 weeks)
- Monitor systemic inflammation (weekly ESR, CRP)
- Family members throat swabbed and treated (Public health)
- Education about ARF and sore throats
- Penicillin intramuscular injections every 4 weeks for next 10 years
- Strep pyogenes susceptible to penicillin but staph aureus produces betalactamase thus resistant –> requires flucloxacillin
Penicillin
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)
Route of excretion for penicillin
GFR and tubular secretion
Differences between the SA and ARF
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)