FCPS Paediatrics TOACS · Interactive Station

✅ Candidate's answer:
• Diagnosis: Serum sickness-like reaction (SSLR) – most likely, though serum sickness is a possibility.
• Classic triad (3 cardinal features):
1️⃣ Fever – usually 38-39°C, occurring 7-14 days after drug exposure.
2️⃣ Rash – typically urticarial (hives), but can be morbilliform or erythema multiforme-like.
3️⃣ Arthralgias/arthritis – symmetric or asymmetric, often involving large joints (knees, ankles, elbows).
• Additional features: Lymphadenopathy (often generalized or cervical), myalgia, malaise, periorbital or peripheral edema.
• This patient has all three cardinal features (fever, urticarial rash, arthralgias) 10 days after starting cefaclor – classic for SSLR.

✅ Candidate's answer:
• True serum sickness (Type III hypersensitivity):
- Caused by immune complex deposition (antigen-antibody complexes) in blood vessels and tissues.
- Associated with heterologous proteins (e.g., horse-derived antivenom, antithymocyte globulin, infliximab) and some drugs (penicillins, sulfonamides).
- Laboratory findings: Hypocomplementemia (low C3, C4), elevated ESR/CRP, possible proteinuria or hematuria (vasculitis).
- May cause vasculitis, glomerulonephritis, or carditis (rare).
• Serum sickness-like reaction (SSLR):
- Clinically similar to serum sickness but no immune complexes and normal complement levels.
- More common in children.
- Common triggers: Cefaclor (most common), other cephalosporins, penicillins, sulfonamides, minocycline, bupropion.
- No vasculitis or organ involvement – limited to skin, joints, lymph nodes.
- Laboratory findings: Normal complement (C3, C4), elevated ESR/CRP, no proteinuria/hematuria.
• This patient likely has SSLR (cefaclor is a classic trigger), but complement testing would differentiate.

✅ Candidate's answer:
• True serum sickness (Type III hypersensitivity):
- Days 1-7: Drug or foreign protein acts as an antigen → B cells produce specific IgG/IgM antibodies.
- Day 7-14: Antigen-antibody complexes form in slight antigen excess → complexes deposit in vessel walls, joints, kidneys, skin.
- Complement activation → recruitment of neutrophils → tissue damage (vasculitis, arthritis, urticaria).
• Serum sickness-like reaction (SSLR):
- Mechanism is not fully understood, but NO immune complexes or complement activation.
- May be due to direct T-cell activation or drug-induced cytokine release.
- Clinically identical to serum sickness but without vasculitis or organ damage.
• Why 7-14 days? Time required for primary immune response (antibody production) after first exposure to the antigen. If the patient was previously sensitized, reaction can occur within 1-3 days (accelerated).

✅ Candidate's answer:
• Serum sickness / serum sickness-like reaction – most likely.
• Kawasaki disease: Fever >5 days, bilateral conjunctival injection, oral mucosal changes (strawberry tongue, fissured lips), polymorphous rash, cervical lymphadenopathy (>1.5 cm), extremity changes (edema, desquamation). This patient has NO oral or conjunctival changes.
• Juvenile idiopathic arthritis (JIA), systemic onset (Still disease): Daily high fevers (>39°C) with quotidian pattern, salmon-pink rash, arthralgias/arthritis. No drug exposure history; chronic course.
• Urticarial vasculitis: Urticarial lesions lasting >24 hours, with palpable purpura, burning sensation (not itching), possible hypocomplementemia. Skin biopsy shows leukocytoclastic vasculitis.
• Viral exanthem (e.g., EBV, parvovirus B19, enterovirus): Often associated with pharyngitis, coryza, or other viral symptoms; no temporal relationship with drug.
• Drug reaction with eosinophilia and systemic symptoms (DRESS): Fever, rash, eosinophilia, atypical lymphocytosis, organ involvement (hepatitis, nephritis). Onset 2-8 weeks after drug start.
• This patient's history (cefaclor exposure, onset day 8-10, urticarial rash, arthralgias, no mucosal changes) strongly favors SSLR.

✅ Candidate's answer:
• Immediate step: Discontinue the offending drug – cefaclor (and any other cephalosporin or β-lactam antibiotic).
• Symptomatic treatment:
1️⃣ Antihistamines for urticaria and pruritus:
- Oral cetirizine (0.25 mg/kg, max 10 mg) or diphenhydramine (1 mg/kg, max 50 mg).
2️⃣ NSAIDs for arthralgias/fever:
- Ibuprofen (10 mg/kg/dose q6-8h) or naproxen.
3️⃣ Cool compresses for rash.
• If symptoms are severe (high fever, significant joint swelling, severe rash):
- Oral corticosteroids (prednisone 1-2 mg/kg/day for 3-7 days, then taper).
• Monitoring: Observe for progression (though most cases resolve within 1-2 weeks after drug discontinuation).
• Do NOT restart cefaclor or give another cephalosporin unless allergy testing is performed.

✅ Candidate's answer:
• To support SSLR and rule out more serious conditions:
1️⃣ Complete blood count (CBC) with differential: May show leukocytosis, normal or elevated eosinophils (not as high as in DRESS).
2️⃣ Inflammatory markers: ESR, CRP – elevated (non-specific).
3️⃣ Complement levels (C3, C4): Normal in SSLR; low in true serum sickness and some autoimmune conditions.
4️⃣ Urinalysis: To rule out glomerulonephritis (proteinuria, hematuria – would indicate true serum sickness).
5️⃣ Liver and renal function tests: To rule out DRESS or systemic involvement.
6️⃣ Antinuclear antibody (ANA), rheumatoid factor (RF): To rule out JIA or SLE.
7️⃣ If Kawasaki disease is suspected: Echocardiogram (for coronary artery dilation).
• This patient likely has normal complement and urinalysis (SSLR).

✅ Candidate's answer:
• Corticosteroids are NOT routinely required for mild SSLR. They are reserved for severe cases with:
- High fever (>39°C) not responding to NSAIDs.
- Severe, debilitating arthralgias or arthritis (inability to walk).
- Extensive, painful urticaria.
- Significant lymphadenopathy or edema.
- True serum sickness with vasculitis or renal involvement.
• Dose: Prednisone 1-2 mg/kg/day (max 60 mg/day) orally once daily.
• Duration: 3-7 days (short course). Tapering may not be necessary for short courses (<7 days), but can be tapered over 1-2 weeks if symptoms were severe.
• Monitor for improvement within 24-48 hours. If no improvement, reconsider diagnosis.
• This patient (mild symptoms) does not need steroids – treat with antihistamines and NSAIDs.

✅ Candidate's answer:
• SSLR to cefaclor is not a contraindication to all cephalosporins or penicillins, but caution is advised.
• Cefaclor is a second-generation cephalosporin. There is low cross-reactivity between different generations of cephalosporins for SSLR.
• However, if the reaction was severe (e.g., Stevens-Johnson syndrome, DRESS), all cephalosporins should be avoided.
• Penicillins: There is no cross-reactivity between cefaclor and penicillins for SSLR (different chemical structure). However, if the patient has a true IgE-mediated penicillin allergy, cross-reactivity with cephalosporins is <2%.
• Recommendation:
- Avoid cefaclor specifically.
- Other cephalosporins may be used if clinically necessary, but under observation (graded challenge in a controlled setting if high-risk).
- Penicillins are likely safe (no cross-reactivity for SSLR).
- Refer to allergist for drug allergy testing and guidance.

✅ Candidate's answer:
• Excellent prognosis with prompt discontinuation of the offending drug.
• Clinical course:
- After stopping the drug, symptoms usually begin to improve within 24-48 hours.
- Rash and arthralgias resolve over 3-7 days.
- Fever resolves within 1-3 days.
- Complete resolution typically within 1-2 weeks.
• Without discontinuation of the drug, symptoms may persist or worsen.
• No long-term sequelae – SSLR does not cause chronic arthritis or autoimmune disease.
• Recurrence: If the same drug is taken again, the reaction can recur, often more rapidly (within 1-3 days).
• This patient should recover completely within 1 week after stopping cefaclor.

✅ Candidate's answer:
• Yes, referral to an allergist is recommended.
• Reasons:
1️⃣ Confirmation of the diagnosis – differentiate from true serum sickness, DRESS, or other drug hypersensitivity reactions.
2️⃣ Testing for drug allergy: Skin testing for cephalosporins may be performed (though not standardized for cefaclor).
3️⃣ Guidance on future antibiotic use: Determine whether other cephalosporins or penicillins can be safely used.
4️⃣ Drug challenge: If an alternative β-lactam is needed, a graded challenge may be performed under supervision.
5️⃣ Education for the family: Clear documentation of the reaction and future avoidance strategies.
6️⃣ Medical alert bracelet: May be recommended for severe reactions.
- This child should be referred to an allergist for evaluation and management.

✅ Candidate's answer:
• Cefaclor (oral cephalosporin) – most common cause of SSLR in children.
• Other antibiotics: Penicillins (amoxicillin, ampicillin), sulfonamides (trimethoprim-sulfamethoxazole), minocycline.
• Anticonvulsants: Phenytoin, carbamazepine, lamotrigine.
• NSAIDs and aspirin – less common.
• Biologics: Infliximab, rituximab, omalizumab (true serum sickness).
• Vaccines: Rare (e.g., tetanus toxoid, rabies vaccine).
• This patient's reaction to cefaclor is classic.

✅ Candidate's answer:
• SSLR:
- Onset: 7-14 days after drug start.
- Rash: Urticarial (hives) – pruritic.
- Fever, arthralgias, lymphadenopathy.
- No internal organ involvement (no hepatitis, nephritis, pneumonitis).
- Eosinophilia: Usually absent or mild.
- Atypical lymphocytes: Absent.
- Prognosis: Excellent, resolves quickly after drug cessation.
• DRESS (drug reaction with eosinophilia and systemic symptoms):
- Onset: 2-8 weeks (delayed).
- Rash: Morbilliform or erythroderma, may progress to exfoliative dermatitis.
- Fever, facial edema, lymphadenopathy.
- Internal organ involvement: Hepatitis (most common), nephritis, pneumonitis, myocarditis.
- Eosinophilia (>1500/μL), atypical lymphocytes.
- Severe, potentially fatal (mortality 5-10%).
- Can reactivate herpesviruses (HHV-6, EBV, CMV).
- Treatment: Systemic corticosteroids, sometimes IVIG.
• This patient (urticarial rash, no organ involvement) is consistent with SSLR, not DRESS.

✅ Candidate's structured answer:
• “Your son had a reaction called serum sickness-like reaction. It is a type of allergic reaction to the antibiotic cefaclor. It is not anaphylaxis (no breathing problems), but it can be uncomfortable.”
• “The good news is that this reaction is temporary. Now that we have stopped the antibiotic, he should start feeling better in 1-2 days. The rash and joint pain will go away completely within a week.”
• “He will need to avoid cefaclor and possibly other cephalosporin antibiotics in the future. If he needs antibiotics again, tell any doctor about this reaction. Penicillins (like amoxicillin) are likely safe, but we will refer you to an allergist to be sure.”
• “This was not a life-threatening reaction, but it was uncomfortable. We will treat his symptoms with antihistamines for the itching and ibuprofen for the joint pain.”
• “If his symptoms worsen (high fever, trouble breathing, swelling of the face or throat), bring him back immediately. But that is unlikely.”
• “You did the right thing by bringing him in. We will take good care of him, and he will be fine.”

✅ Candidate's answer:
• Documentation in medical record:
- Clear allergy label: “Cefaclor – serum sickness-like reaction (fever, urticaria, arthralgias).”
- Date of reaction, symptoms, duration of treatment.
- Avoid cefaclor specifically; caution with other cephalosporins.
• Precautions for future antibiotics:
1️⃣ Avoid cefaclor.
2️⃣ Other cephalosporins may be used with caution (if clinically necessary) – consider graded challenge under allergist supervision.
3️⃣ Penicillins (amoxicillin, etc.) are likely safe (no cross-reactivity for SSLR).
4️⃣ If the child has a severe infection requiring a cephalosporin (e.g., meningitis), consult allergist for skin testing and possible desensitization.
5️⃣ Alert family to inform all healthcare providers about this reaction.
- This child should have an allergy bracelet only if recommended by an allergist.