A previously healthy 4-year-old boy is brought to the physician by his parents because he has had a fever, diffuse joint pain, and a rash on his abdomen for the past week. Acetaminophen did not improve his symptoms. He emigrated from China with his family 2 years ago. He attends daycare. His immunization records are not available. His temperature is 38.5°C (101.3°F), pulse is 125/min, and blood pressure is 100/60 mm Hg. Examination shows polymorphous truncal rash. The eyes are pink with no exudate. The tongue is shiny and red, and the lips are cracked. The hands and feet are red and swollen. There is right-sided anterior cervical lymphadenopathy. Which of the following is the most appropriate next step in management?

HHV-6 immunoglobulin M (IgM) detection

Antistreptolysin O titer measurement

A 53-year-old woman comes to the physician in February because of a 1-day history of fever, chills, headache, and dry cough. She also reports malaise and generalized muscle aches. She works as a teacher at a local high school, where there was recently an outbreak of influenza. She has a history of intermittent asthma, for which she takes albuterol as needed. She declined the influenza vaccine offered in the fall because her sister told her that a friend developed a flulike illness after receiving the vaccine. She is worried about possibly becoming ill and cannot afford to miss work. Her temperature is 37.9°C (100.3°F), heart rate is 58/min, and her respirations are 12/min. Physical examination is unremarkable. Her hemoglobin concentration is 14.5 g/dL, leukocyte count is 9,400/mm3, and platelet count is 280,000/mm3. In addition to analgesia, which of the following is the most appropriate next step in management?

Live attenuated influenza vaccine

A 4-year-old boy is brought to a pediatrician by his parents with a history of fever for the last 5 days and irritability, decreased appetite, vomiting, and swelling of the hands and feet for the last 3 days. The patient’s mother mentions that he has been taking antibiotics and antipyretics prescribed by another physician for the last 3 days, but there has been no improvement His temperature is 39.4°C (103.0°F), pulse is 128/min, respiratory rate is 24/min, and blood pressure is 96/64 mm Hg. On physical examination, there is significant edema of the hands and feet bilaterally. There is a 2.5 cm diameter freely moveable, nontender cervical lymph node is palpable on the right side. A strawberry tongue and perianal erythema are noted. Conjunctival injection is present bilaterally. Laboratory findings reveal mild anemia and a leukocytosis with a left-shift. Erythrocyte sedimentation rate (ESR) and serum C-reactive protein (CRP) are increased. If not treated appropriately, this patient is at increased risk of developing which of the following complications?

Lower gastrointestinal hemorrhage

Acute disseminated encephalomyelitis (ADEM)

A 5-year-old girl presents with a rash and a persistent fever of 41.0°C (105.8°F), not relieved by Tylenol. The patient's mother says that her symptoms started 5 days ago and have not improved. The rash started on her trunk and now is present everywhere including the palms and soles. Her birth history is normal. Her pulse is 120/min and respiratory rate is 22/min. On physical examination, the patient is agitated and ill-appearing. There is significant swelling of the distal upper and lower extremities bilaterally. The pharynx is hyperemic (see image). Generalized edema with palpable cervical lymphadenopathy is noted. Muscle tone is normal. Remainder of exam is unremarkable. Laboratory findings are significant for the following: Laboratory test Hb 9 g/dL RBC 3.3/mm3 Neutrophilic leukocytosis 28,000/mm3 Normal platelet count 200,000/mm3 Serum ɣ-GT increased Hyperbilirubinemia 2.98 mg/dL AST and ALT are normal, but there is markedly increased serum CRP. Which of the following is the most likely diagnosis in this patient?

Staphylococcal scalded skin syndrome

A previously healthy 3-year-old girl is brought to the physician by her parents for the evaluation of recurrent episodes of pain in her left wrist and right knee for 4 months. She has not had any trauma to the knee or any previous problems with her joints. She attends daycare. Her mother has rheumatoid arthritis. Her vital signs are within normal limits. Examination of the right knee and left wrist shows mild swelling, tenderness, warmth, and erythema; range of motion is slightly decreased. No other joints are affected. The remainder of the examination shows no abnormalities. Laboratory studies show: Hemoglobin 12.4 g/dL Leukocyte count 9,000/mm3 Platelet count 200,000/mm3 Erythrocyte sedimentation rate 50 mm/h Serum Antinuclear antibodies 1:320 Rheumatoid factor negative This patient is at increased risk for which of the following complications?

Inflammation of sacroiliac joints

IVIG resistance for USMLE Step 3: High-Yield Pediatrics Lessons

Definition & Risk Scores - The Unyielding Fever

IVIG Resistance: Defined as persistent or recrudescent fever (≥38°C) lasting for ≥36 hours after the completion of the initial IVIG infusion. This affects up to 20% of Kawasaki disease patients.
Key Laboratory Predictors for Resistance:
- ↑ C-reactive protein (CRP) >8 mg/dL
- ↑ Neutrophil count >80%
- ↓ Serum albumin <3.5 g/dL
- ↓ Sodium <135 mEq/L
- ↑ Alanine transaminase (ALT)
Clinical Risk Scoring Systems:

Parameter	Kobayashi Score (≥5 pts)	Egami Score (≥3 pts)
Age	≤12 months (1 pt)	≤6 months (1 pt)
Sodium	≤133 mEq/L (2 pts)	-
AST	≥100 IU/L (2 pts)	-
Platelets	≤30.0 x10⁴/μL (1 pt)	-
CRP	≥10 mg/dL (1 pt)	≥8 mg/dL (1 pt)
Neutrophils	≥80% (2 pts)	-
Albumin	-	≤3.5 g/dL (1 pt)

Treatment Algorithm - Plan B Protocols

Management of patients who remain febrile ≥ 36 hours after the initial IVIG infusion.

⭐ Patients with IVIG-resistant Kawasaki disease have a significantly higher risk (up to 25%) of developing coronary artery aneurysms compared to responders.

Complications & Monitoring - The Artery Attack

IVIG resistance significantly ↑ risk of Coronary Artery Aneurysms (CAA), the hallmark complication.

Risk Profile:
- Untreated: ~25% develop CAA.
- IVIG-Treated: Risk ↓ to <5%.
- IVIG-Resistant: Risk is substantially higher, mandating aggressive follow-up.
Monitoring:
- Intensified surveillance with serial echocardiography is crucial to track coronary artery dimensions and function.
Other Complications:
- Myocarditis
- Macrophage Activation Syndrome (MAS)

⭐ Most coronary artery changes develop within the first 4 weeks after fever onset. Early detection is key.

Echocardiogram of giant coronary artery aneurysms in KD

High‑Yield Points - ⚡ Biggest Takeaways

IVIG resistance is defined as persistent or recrudescent fever ≥36 hours after completing the initial IVIG infusion.

It is the strongest predictor for the development of coronary artery aneurysms (CAA).

High-risk patients can be identified by scoring systems like the Kobayashi score.

The standard second-line treatment is another dose of IVIG (2 g/kg).

For refractory cases, treatment options include corticosteroids (prednisolone) or infliximab.

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IVIG resistance