Lecture 15 - Septic Arthritis and Rheumatic Fever Flashcards
M protien?
used in differentiating Grp A streptococcal types, virulence factor, resistance to phagocytosis
Septic arthritis?
occurs most frequently in childhood, fever and malaise, swelling and tenderness around affected joint, clinically joint is held in position with most intracapsular volume
Why children?
unfused growht plates, highly vascular
Septic arthritis diagnosis?
difficult, early diagnosis prevents irreversible damage to growth plates, lower extremities most common, staph. aureus and strep. pyogenes, drainage and washout required for treatment and diagnosis, IV antibiotics initiall, and thn long course (2-3wk)
Acute rheumatic fever?
auto-immune infection following strep. pyogenes pharyngitis, generalised inflammation, rheumatic heart disease complication (mitral and/or aortic valves), several week latent period before symtpoms
Major diagnosis criteria of ARF?
carditis, polyarthritis, sydenhams chorea, rash, nodules PLUS evidence of preceding strep infection (elevated antibodies or positive gram A throat culture)
Heart diagnostics of rheumatic fever?
elongated PR interval (from carditis), murmer (mitral regurgitation), painful polyarthritis (typically asymmetrical and migratory)
Movement disorder?
Sydenhams chorea, inability to stop moving, darting tongue, auto antibody-mediated neuronal cell-signalling in cerebrospinal fluid
Erythema marginatum?
rare, characteristic skin rash, on limbs not face, spread outwards in circular shape edges raised centre clears, symptom free commonly unnoticed
Cause of autoimmune response?
similarity of human cardiac myosin and streptoccocal M protein, antibodies cross react with collagen or cardiac valvular endothelia antigens then T cells infiltrate causing inflammation (arthritis) and then long term damage (carditis and ARF)
Reccurent attacks?
after initial ARF attack and carditis, valves scar and nevascularise which perpetuates disease, this is why preventing recurrencies is essential
Diagnosis?
negative throat culture does not rule out, nor does positive culture mean infection, ASO and anti-DNase B titres measured, highest 3-6 wk after infection and months to decline
Protective methods following diagnosis?
2wk bed rest, monitor systemic inflammation, throat swab family, educate, I.M. penicillin every 4wk for decade
Penicillin action?
resembles NAM and binds transpeptidase (inhibitory) to destroy cell wall
IV penicillin?
rapid peak, rapid clearance, used for meningitis, pneumonia and septic arthritis
I.M penicillin (Benathine pen G)?
1-2% of iV peak, but measurable amount lasts 3 weeks, pain risk at site, used fro group A strep in impetigo, and prophylaxis of strep sore throat in RF
Penicillin excretion?
GFR and tubular secretion
Septic arthritis vs RF - age?
any age up till 10, vs school age (5-15)
SA vs RF - physiology?
active infection arthritis due to aureus and pyogenes infection of joint capsule, vs. multisystem inflammatory disease (heat, skin, brain involvement)
SA vs RF - treatment?
cleaning joint and penicillin to clear infection, vs. long term penicillin to prevent recurrence
