An 11-year-old boy presents with fever and joint pain for the last 3 days. His mother says that he had a sore throat 3 weeks ago but did not seek medical care at that time. The family immigrated from the Middle East 3 years ago. The patient has no past medical history. The current illness started with a fever and a swollen right knee that was very painful. The following day, his knee improved but his left elbow became swollen and painful. While in the waiting room, his left knee is also becoming swollen and painful. Vital signs include: temperature 38.7°C (101.6°F), and blood pressure 110/80 mm Hg. On physical examination, the affected joints are swollen and very tender to touch, and there are circular areas of redness on his back and left forearm (as shown in the image). Which of the following is needed to establish a diagnosis of acute rheumatic fever in this patient?

Positive anti-streptococcal serology

Elevated erythrocyte sedimentation rate (ESR)

No other criterion is needed to establish the diagnosis of acute rheumatic fever

A 14-year-old girl is brought to the physician because of a 1-week history of fever, malaise, and chest pain. She describes the pain as 6 out of 10 in intensity and that it is more severe if she takes a deep breath. The pain is centrally located in the chest and does not radiate. Three weeks ago, she had a sore throat that resolved without treatment. She has no personal history of serious illness. She appears ill. Her temperature is 38.7°C (101.7°F). Examination shows several subcutaneous nodules on the elbows and wrist bilaterally. Breath sounds are normal. A soft early systolic murmur is heard best at the apex in the left lateral position. Abdominal examination is unremarkable. Laboratory studies show: Hemoglobin 12.6 g/dL Leukocyte count 12,300/mm3 Platelet count 230,000/mm3 Erythrocyte sedimentation rate 40 mm/hr Serum Antistreptolysin O titer 327 U/mL (N < 200 U/mL) She is treated with aspirin and penicillin and her symptoms resolve. An echocardiography of the heart done 14 days later shows no abnormalities. Which of the following is the most appropriate next step in management?

Intramuscular benzathine penicillin every 4 weeks for 10 years

Intramuscular benzathine penicillin every 4 weeks until the age of 21

Intramuscular benzathine penicillin every 4 weeks for 5 years

Intramuscular benzathine penicillin every 4 weeks until the age of 40

Low-dose prednisone therapy for a month

Post-infectious immune complications for USMLE Step 1: High-Yield Pediatrics Lessons

Acute Rheumatic Fever - Heartbreak Fever

Post-infectious sequel of Group A Strep pharyngitis (Type II HSR). Primarily affects children 5-15 years.
Diagnosis: 2 Major OR 1 Major + 2 Minor criteria, plus evidence of preceding GAS infection (↑ASO/Anti-DNase B).
📌 JONES Criteria (Major):
- Joints: Migratory polyarthritis (large joints).
- O (Carditis): Pancarditis. Aschoff bodies are pathognomonic.
- Nodules: Subcutaneous, painless, on extensor surfaces.
- Erythema marginatum: Evanescent, non-pruritic rash with central clearing.
- Sydenham chorea: "St. Vitus' dance," late finding.

⭐ Carditis is the most serious manifestation, and the only one causing permanent damage. The mitral valve is most commonly affected (leading to regurgitation).

Management: Penicillin + Aspirin. Prophylaxis with Benzathine Penicillin G is crucial.

Post-Streptococcal GN - Sore Throat, Sore Kidney

Type III HSR triggered by nephritogenic strains of Group A Streptococcus.
Presents 1-2 weeks after pharyngitis or 3-6 weeks after impetigo.
Classic triad: periorbital edema, hypertension, and cola-colored urine (hematuria).
Key labs: ↑ Anti-streptolysin O (ASO) or Anti-DNase B titers, ↓ serum $C_3$ levels.
Kidney Biopsy findings:
- LM: Diffusely hypercellular, proliferative glomeruli.
- IF: Granular "lumpy-bumpy" deposits of IgG & C3.
- EM: Subepithelial electron-dense deposits or "humps".

⭐ Low $C_3$ is the hallmark; it typically normalizes within 6-8 weeks.

Kidney biopsy in post-streptococcal glomerulonephritis

Kawasaki Disease - Fiery Vessel Fury

Acute febrile vasculitis of medium-sized arteries, typically in children < 5 years. Also known as Mucocutaneous Lymph Node Syndrome.
Diagnosis: Fever for ≥ 5 days + ≥ 4 of the following criteria:
- 📌 CRASH: Conjunctivitis (bilateral, non-exudative), Rash (polymorphous), Adenopathy (unilateral cervical, >1.5 cm), Strawberry tongue & lip fissures, Hand/foot edema, erythema, or desquamation.
Treatment: High-dose IVIG (2 g/kg) + high-dose Aspirin.

⭐ The most feared complication is coronary artery aneurysms, which are monitored with 2D-Echocardiography.

GBS & HSP - Nerve Tingles, Purple Shingles

Guillain-Barré (GBS): Acute, ascending, areflexic paralysis. Post-Campylobacter trigger common.
- Patho: Autoimmune demyelination of peripheral nerves.
- CSF: ↑ Protein, normal cells (albuminocytologic dissociation).
- Rx: IVIg or plasmapheresis.
Henoch-Schönlein Purpura (HSP): IgA-mediated small vessel vasculitis.
- Classic Tetrad: Palpable purpura (buttocks/legs), arthralgia, abdominal pain, hematuria.
- Platelets: Normal.
- Rx: Supportive care. Steroids for severe renal/GI symptoms.

⭐ HSP Nephritis: Major cause of long-term morbidity. Monitor urine for hematuria/proteinuria.

Palpable purpura in Henoch-Schönlein Purpura

High‑Yield Points - ⚡ Biggest Takeaways

Acute Rheumatic Fever (ARF) follows streptococcal pharyngitis (not skin infection) and is diagnosed via Jones criteria.

Post-Streptococcal Glomerulonephritis (PSGN) follows pharyngitis or skin infection, causing a nephritic syndrome with low C3.

Guillain-Barré Syndrome (GBS) presents as ascending paralysis with areflexia, often post-Campylobacter infection.

CSF in GBS shows albuminocytologic dissociation (↑ protein, normal cells).

Kawasaki Disease's primary risk is coronary artery aneurysms; treat with IVIG and aspirin.

Henoch-Schönlein Purpura (HSP) is an IgA vasculitis causing palpable purpura on the lower limbs.

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