A 9-month-old boy is brought to the physician because of increased irritability, continual crying, and fever for 1 day. His mother has noticed that he refuses to lie down on his right side and keeps tugging at his right ear. One week ago, he had a runny nose that has since improved. He was born at term and has been otherwise healthy. He was exclusively breastfed until 2 months of age and is currently bottle-fed with some solid foods introduced. He has been attending a daycare center for the past 5 months. His temperature is 38.4°C (101.1°F) and pulse is 144/min. Otoscopic examination in this child is most likely to show which of the following?

Bulging erythematous tympanic membrane

Erythematous external auditory canal

Brown mass within the ear canal

Retracted opacified tympanic membrane

A 6-month-old girl presents to an outpatient office for a routine physical. She can sit momentarily propped on her hands, babbles with consonants, and transfers objects hand to hand. The pediatrician assures the parents that their daughter has reached appropriate developmental milestones. Which additional milestone would be expected at this stage in development?

Showing an object to her parents to share her interest in that object

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 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

Age-specific considerations for USMLE Step 2 CK: High-Yield Pediatrics Lessons

Infants (<1 year) - Tiny Tempers, Big Trouble

Diagnostic challenge is high as incomplete/atypical presentation is the rule, not the exception. Maintain a high index of suspicion.

Core Features (Often Incomplete):
- Prolonged, unexplained fever (>5 days) is the most consistent finding.
- Extreme, inconsolable irritability is a hallmark sign.
- Sterile pyuria (WBCs in urine without bacterial growth).
Key Lab Markers:
- ↑ CRP (>3 mg/dL) and/or ↑ ESR (>40 mm/hr).
- Thrombocytosis (platelets >450,000/μL), typically appears late (after week 1).
- Hypoalbuminemia (<3 g/dL).

⭐ Infants with Kawasaki Disease have the highest risk of developing giant coronary artery aneurysms (CAA), leading to long-term cardiac morbidity.

Kawasaki Disease Complication Timeline & Imaging

Toddlers & Children (1-5 yrs) - The Classic CRASH

This age group typically presents with the classic form of Kawasaki disease: a high-grade fever lasting ≥5 days plus at least four principal clinical features.

📌 Mnemonic: CRASH & Burn (Fever)

Principal Criteria (≥4 of 5):
- Conjunctivitis: Bilateral, non-purulent, bulbar injection.
- Rash: Polymorphous (maculopapular, morbilliform), non-bullous, often perineal accentuation.
- Adenopathy: Unilateral cervical lymph node >1.5 cm.
- Strawberry tongue & Lip changes: Erythema, fissuring, and cracking of lips.
- Hand & Foot changes: Indurative edema and erythema of palms/soles, followed by periungual desquamation.

Kawasaki disease symptoms and long-term cardiac effects

Coronary Artery Aneurysm (CAA) Risk: Lower than in infants, but remains a significant concern. Prompt IVIG is critical.

⭐ Exam Favourite: Prominent, tender, unilateral cervical lymphadenopathy is a very common feature in this age group, sometimes being the most striking sign.

Incomplete vs. Atypical KD - The Diagnostic Dilemma

Incomplete KD: Classic fever pattern (≥5 days) but with only 2-3 principal clinical criteria. Diagnosis requires high suspicion.
Atypical KD: Fulfills criteria for KD but presents with unusual, organ-specific findings like renal impairment, facial nerve palsy, or severe arthritis.

The crucial step for suspected Incomplete KD is following the AHA algorithm, triggered by elevated inflammatory markers.

⭐ Infants (<6 months) with unexplained fever for ≥7 days should be evaluated for KD even with no clinical criteria, as they have the highest risk for coronary artery aneurysms.

Infants <6 months face the highest risk for developing coronary artery aneurysms (CAA).

Incomplete Kawasaki disease is most frequent in infants, often leading to delayed diagnosis and treatment.

In young infants, prolonged fever and irritability might be the only presenting signs.

Older children (>5 years) are more likely to show atypical manifestations like significant arthritis or renal impairment.

IVIG resistance is notably more common in the infant population.

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