Lecture 15: Septic Arthritis and Rheumatic Fever

Question 1

GAS appearance?

Answer 1

Group A Strep = B-haemolytic stretococci in chains (gram positive)

There are lots of types that are recognised by their surface M proteins that resist phagocytosis and are an important virulence factor.

They produce streptolysins and NADase etc. that your body produces antibodies against that can be tested for.

Question 2

What is septic arthritis? Presentation?

Answer 2

An example of a suppurative complication of Grp A Strep

• Presence of infection from bacteria in bone and marrow andor joint space
• Most frequent in children <10 (due to growth plates)
• Generalised systemic symptoms include fever and malaise
• Swelling, erythema and tenderness arounf the affected joint
• Clinically joint held in position that maximises intracapsular volume

Question 3

What is Acute Rheumatic Fever?

Answer 3

An auto-immune response following throat infection with Streptococcus pyogenes (although sometimes no sore throat is ever felt or can have a 2 weeks of latency phase)

Generalised inflammation: attacking certain parts of the body - heart, joints and/or brain

Can cause lasting damage to mitral and/or aortic valves = rheumatic heart disease

Question 4

Arthritis in Rheumatic fever?

Answer 4

• The commonest presenting symptom of acute rheumtic fever - up to 75% of first attacks
• Typically ARF is extremeyl painful and unable to bear weight
• Large joints usually affected (esp knees and ankles)
• Polyarthritis is usually asymmetrical and migratory

Question 5

Major and minor symptoms of rheumatic fever?

Answer 5

Major:

• Carditis
• Polyarthritis
• Sydenhams Chorea (inability to keep still)
• Erythema Marginatum (very uncommon rash on upper arms and legs but not the face)
• Subcutaneous nodules (very very rare)

Minor:

• Fever
• polyarthralgia
• raised acute phase reactants

Question 6

Mechanism or ARF?

Answer 6

Autoimmune mechanism related to molecular mimicry

• Normal host response to group A streptococcus to 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 (eg. human cardiac myosin and streptococcal M protein are likely impotant antigens in pathogenesis of RHD)
• Antibodies can cross react with collagen leading to T cell infiltration and inflammation (arthritis)

Preventing recurrences is of the upmost importance

• Auto antibody-mediated neuronal cell signalling in CSF may be part of chorea

Question 7

Importance of streptococcal antibody titres?

Answer 7

• Most ARF cases do not have culture positive throat and even when it is positive it can just represent carriage and does not confirm recent infection.
• Tests used are plasma antistreptolysin O (ASO) and the antideoxyribonuclease B (Anti-DNaseB) titres.
• ASO highest at 3-6 weeks post infection and can take 2 months to decline and 6 months till normal.

Question 8

Treatment for ARF?

Answer 8

• Bed rested in hospital for 2 weeks
• Monitor systemic inflammation (weekly ESR, CRP)
• Family members throats swabbed and tested
• Education about ARF and sore throats
• Penicillin IM every 4 weeks for next 10 years (or until 21)

Question 9

Different forms of penicillin?

Answer 9

Aqueous (water soluable) 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

Benzathine pen G (IM injection)

• Low conc of serum penicillin G (1-2% of aqueous) BUT detectable amounts upto 3 weeks
• pain at injection site is an issue
• Appropriate for highly sensitive bacteria in highly vascularised areas and is used for GAS in impetigo and prophylaxis in sore throat rheumatic fever patients

BOTH ARE EXCRETED BY GFR AND TUBULAR SECRETION

Question 10

SEPTIC ARTHRITIS vs ACUTE Rh FEVER

• age
• presentation
• treatment

Answer 10