L13. Septic arthritis and Rheumatic fever

Question 1

What are the differential diagnoses for

-hot swollen knee joints, child with fever

Answer 1

septic arthritis and acute rheumatic fever

• other reactive arthritis (eg. rheumatoid)
• trauma/muscular injury + other illness - bc not usually fever alone)

Question 2

What are the different types of acute pus forming (suppurative) diseases caused by Group A strep (pyogenes)

and nonsuppurative types: delayed sequelae which follow uncomplicated infections

Answer 2

Suppurative

• SSTI: impetigo, cellulitis
• streptococcal toxic shock syndrome
• pharyngitis and tonsilitis; scarlet fever
• Septic arthritis

Non-suppurative

• acute rheumatic fever leading to rheumatic heart disease.
• post streptococcal glomerulonephritis

Question 3

What is the presentation, pathogenesis, bacterial agent and high risk groups for Septic Arthritis

Answer 3

Septic arthritis presents as swelling, erythema, heat and pain/tenderness around an affected joint.- generally knee down

• Accompanied by fever and rapid malaise
• joint often held in flexed/ position that maximises intracapsular volume, minimises movement.

It is caused by bacteria in bone and marrow and/or joint space -coming from skin–>blood
1. Staph A. 2. Strep pyogenes

High risk groups is children/bbs <10yrold because have very vascular epiphyseal plate which is a portal of entry for bacteria

Question 4

How is septic arthritis diagnosed and treated. What is the complications of late treatment

Answer 4

1.diagnosed by culture of joint aspirate

2. Treatment by
   - 2 joint washouts over consecutive days to get rid of the pus
   - IV antibiotics for 2 weeks, then oral amoxycillin for 1 week (for Gp A strep infection)
3. complications irreversible growth plate disruption

Question 5

What is the pathogenesis of acute Rheumatic fever and how does it progress to rheumatic heart disease

Answer 5

1. Infection with Grp A strep- generally throat, but not always
2. triggers production of antibodies against strep A that are cross reactive to host antigens (autoimmune)
3. Latent period of several weeks before symptoms of acute rheumatic fever occur - generalised inflammation of heart, joints, skin +/- brain

• -> rheumatic heart disease
  1. autoimmune response against collagen/cardiac valvular endothelial antigens leading to valve scarring (carditis)

2. Recurrent rheumatic fever attacks increase scar formation and subsequent neovascularisation of the valves which perpetuates disease

Question 6

What are hallmark symptoms of acute rheumatic fever (weeks after actual infection)

generally seen in school age children

Answer 6

1. Polyarthritis of larger joints which is asymmetrical and migratory. (extremely pain, heat, lim movement)

or polyarthralgia (just joint pain)

2. Sydenhams chorea: self limiting; rapid irregular involuntary movements (due to auto-antibody to neuronal cell signalling in CSF.
3. Erythema marginatum: uncommon skin rash with pale centre and red irregular ring on outside
4. subcutaneous nodules (rare)
5. Prolonged P-R interval on ECG due to poor atrial->ventricular conduction,
   - auscultation of new audible murmur due to poor valve closing (regurgitation)

Question 7

How is Gp A strep infection confirmed (as part of diagnostic criteria) and what is the timings of peaks

Answer 7

Streptococcal antibody titres

1. plasma anti-streptolysin
2. antideoxyribonuclease B

these should be highest 3-6 wks after infection which is when most children present with Acute rheumatic fever.

2-4 x increase/decrease in tests 2-3 weeks apart indicates recent infection

Takes 2 mo to decline and 6 mo to return to normal.
v young and patients >15yold have lower levels.

Question 8

What is the treatment for acute rheumatic fever

Answer 8

1. Bed rest for 2 weeks in hospital- in wheelchair to stop progression of carditis
2. Monitoring systemic inflammation using weekly ESR, CRP
3. Family members throat swabbed and treated
4. Education about ARF and sore throat
5. IM injections of benzathine penicillin G every 4 weeks for next 10yrs or until 21.

Question 9

What is the epidemiology of ARF

Answer 9

14x higher in NZ compared to other oecd countries. Was dropping but has come back up after primary prevention of sore throats was scaled back. High rates in northland

Associated with overcrowding, deprivation. highest in Pacific and Maori communities

Question 10

Compare the types of penicillin used to treat Septic arthritis, ARF. mild- moderate infections
- concentrations, duration, good for,

All excreted by GFR and tubular secretion

Answer 10

1. Aqueous penicillin G given IV
   - delivers high concentrations quickly but excreted rapidly within 2-4 hrs
   - good for acute severe infections- eg septic arthritis meningitis, sepsis, pneumonia
2. Benzathine penicillin G given IM
   - delivers v low concentration but detectable amounts in serum >3 wks, so last for long time.
   - good for highly sensitive bacteria in highly vascular areas as it readily diffuses
   - treats gp A for impetigo and prophylaxis of strep sore throat for ARF
3. Oral penicillin (penicillin V)
   - absorbed well from GI tract giving 40% of IV penicillin dose
   - good for pharyngitis, younger children presenting with sore throat (not adult)

Question 11

How is the pain at injection site managed for prophylaxis patients

Answer 11

Lignocaine and buzzy (vibration) helps in less than 13 yolds