A 7-day-old male infant presents to the pediatrician for weight loss. There is no history of excessive crying, irritability, lethargy, or feeding difficulty. The parents deny any history of fast breathing, bluish discoloration of lips/nails, fever, vomiting, diarrhea, or seizures. He was born at full term by vaginal delivery without any perinatal complications and his birth weight was 3.6 kg (8 lb). Since birth he has been exclusively breastfed and passes urine six to eight times a day. His physical examination, including vital signs, is completely normal. His weight is 3.3 kg (7.3 lb); length and head circumference are normal for his age and sex. Which of the following is the next best step in the management of the infant?

Evaluation of the mother for malnutrition

Admission of the infant in the NICU to treat with empiric intravenous antibiotics

Emphasize the need to clothe the infant warmly to prevent hypothermia

Supplementation of breastfeeding with an appropriate infant formula

A 5-year-old boy is brought to the physician because of behavioral problems. His mother says that he has frequent angry outbursts and gets into fights with his classmates. He constantly complains of feeling hungry, even after eating a full meal. He has no siblings, and both of his parents are healthy. He is at the 25th percentile for height and is above the 95th percentile for weight. Physical examination shows central obesity, undescended testes, almond-shaped eyes, and a thin upper lip. Which of the following genetic changes is most likely associated with this patient's condition?

Loss of paternal gene expression on chromosome 15

Mitotic nondisjunction of chromosome 21

Mutation of FBN-1 gene on chromosome 15

Microdeletion of long arm of chromosome 7

Deletion of Phe508 on chromosome 7

A 5-year-old boy presents to the pediatrician for a well child visit. He is meeting his developmental milestones and is in the 15th percentile for height and 70th percentile for weight. His parents report that he complains of fatiguing easily and having trouble participating in sports. They are concerned he is not getting enough sleep and state that sometimes they hear him snore. The patient has a past medical history of a supracondylar fracture of the humerus, which was appropriately treated. He is doing well in school but is sometimes bullied for being small. The patient eats a balanced diet of milk, fruit, and some vegetables. His parents have been trying to get him to drink more milk so he can grow taller. His temperature is 99.5°F (37.5°C), blood pressure is 90/48 mmHg, pulse is 100/min, respirations are 19/min, and oxygen saturation is 98% on room air. On physical exam, the patient appears well. HEENT exam is notable for conjunctival pallor and a unilateral clear middle ear effusion. Cardiac exam reveals a benign flow murmur. Pulmonary exam is clear to auscultation bilaterally. The patient's gait is stable and he is able to jump up and down. A full set of labs are ordered as requested by the parents including a serum vitamin D level, B12 level, and IGF level. A selection of these lab values are seen below. Serum: Na+: 139 mEq/L Cl-: 100 mEq/L K+: 4.3 mEq/L HCO3-: 25 mEq/L BUN: 20 mg/dL Glucose: 99 mg/dL Creatinine: 1.1 mg/dL Ca2+: 9.9 mg/dL AST: 12 U/L ALT: 10 U/L Which of the following would you expect to find in this patient?

Decreased oxygen saturation when the patient sleeps

A 17-year-old girl is brought into the physician's office with complaints of nausea, vomiting, headache, and blurry vision. In preparation for final exams the patient's mother started her on an array of supplements and herbal preparations given the "viral illness" that is prevalent at her school. Despite these remedies, the girl has been feeling perpetually worse, and yesterday during cheerleading practice had to sit out after vomiting and feeling dizzy. The patient admits to falling during one of the exercises and hitting her head on another girl's shin due to her dizziness. When asked to clarify her dizziness, the patient states that she feels rather lightheaded at times. The patient's BMI is 19 kg/m^2. She endorses diarrhea of recent onset, and some non-specific, diffuse pruritus of her skin which she attributes to stress from her finals. The patient has a past medical history of anxiety, depression, and excessive exercise habits. On physical exam the patient is alert and oriented to place, person, and time, and answers questions appropriately. She denies any decreased ability to participate in school or to focus. Her skin is dry and peeling with a minor yellow discoloration. Her memory is intact at 1 minute and 5 minutes for 3 objects. The patient's pupils are equal and reactive to light and there are no abnormalities upon examination of cranial nerve III, IV or VI. Which of the following is the most likely cause of this patient's symptoms?

Idiopathic intracranial hypertension

A 42-year-old woman comes to the physician for a routine health maintenance examination. She has generalized fatigue and has had difficulties doing her household duties for the past 3 months. She has eczema and gastroesophageal reflux disease. She has a history of using intravenous methamphetamine in her youth but has not used illicit drugs in 23 years. Her medications include topical clobetasol and pantoprazole. She is 160 cm (5 ft 3 in) tall and weighs 105 kg (231 lb); BMI is 42 kg/m2. Her temperature is 37°C (98.6°F), pulse is 95/min, and blood pressure is 145/90 mm Hg. The lungs are clear to auscultation. Cardiac examination shows no abnormalities. Pelvic examination shows a normal vagina and cervix. Laboratory studies show: Hemoglobin 13.1 g/dL Leukocyte count 7,800/mm3 Platelet count 312,000/mm3 Serum Na+ 141 mEq/L K+ 4.6 mEq/L Cl- 98 mEq/L Urea nitrogen 12 mg/dL Fasting glucose 110 mg/dL Creatinine 0.8 mg/dL Total cholesterol 269 mg/dL HDL-cholesterol 55 mg/dL LDL-cholesterol 160 mg/dL Triglycerides 320 mg/dL Urinalysis is within normal limits. An x-ray of the chest shows no abnormalities. She has not lost any weight over the past year despite following supervised weight loss programs, including various diets and exercise regimens. Which of the following is the most appropriate next step in management of this patient?

Phentermine and topiramate therapy and follow-up in 3 months

Metformin and statin therapy and follow-up in 3 months

Obesity in children for USMLE Step 1: High-Yield Pediatrics Lessons

Definition & Cutoffs - Sizing Up the Situation

Core Metric: Body Mass Index (BMI) for age and sex, plotted on appropriate growth charts.
IAP / CDC Percentile Cutoffs:
- Underweight: < 5th percentile
- Normal Weight: 5th to < 85th percentile
- Overweight: 85th to < 95th percentile
- Obesity: ≥ 95th percentile
- Severe Obesity: ≥ 120% of the 95th percentile or BMI ≥ 35 kg/m².
WHO Z-Score Cutoffs (< 5 years):
- Overweight: Weight-for-height > +2 SD
- Obesity: Weight-for-height > +3 SD

BMI-for-age percentiles for boys and girls (2-20 years)

⭐ A child with obesity at age 6 has a >50% chance of being obese as an adult, rising to 80% for an obese adolescent.

Etiology & Risks - The Why Behind the Weight

Polygenic & Syndromic:
- Strong genetic predisposition; risk is >80% if both parents are obese.
- Syndromes: Prader-Willi, Bardet-Biedl, Cohen syndrome.
Lifestyle & Environment:
- Diet: ↑ intake of energy-dense foods, sugary beverages (SSBs).
- Activity: ↓ physical activity, ↑ sedentary time (screen time >2 hrs/day).
Perinatal Factors:
- Maternal obesity, Gestational Diabetes (GDM).
- High birth weight (>4 kg), rapid infant weight gain.

⭐ A child with one obese parent has a 40% risk of obesity; this jumps to 80% if both parents are obese.

Complications - The Health Toll

Metabolic/Endocrine
- Insulin Resistance → Type 2 Diabetes Mellitus
- Dyslipidemia (↑ Triglycerides, ↓ HDL)
- Precocious puberty, Polycystic Ovary Syndrome (PCOS) in girls
Gastrointestinal
- Non-alcoholic fatty liver disease (NAFLD) → NASH → Cirrhosis
- Cholelithiasis (gallstones)
Musculoskeletal
- Slipped Capital Femoral Epiphysis (SCFE)
- Blount's Disease (Tibia vara)
- Flat feet, musculoskeletal pain
Cardio-Respiratory
- Hypertension
- Obstructive Sleep Apnea (OSA)
- Asthma exacerbation
Neurological
- Idiopathic Intracranial Hypertension (Pseudotumor cerebri)
Psychological
- Depression, anxiety, low self-esteem & social isolation

⭐ Childhood obesity is the most significant predictor of adult obesity, with >80% of obese adolescents becoming obese adults, carrying forward all associated health risks.

Systemic inflammation in obesity and related comorbidities

Management - The Action Plan

Management follows a staged, escalating process focused on family-centered behavioral changes. The primary goal is not rapid weight loss but achieving healthy eating and activity patterns, allowing the child to "grow into" a healthy weight over time.

📌 Mnemonic: 5-2-1-0 Rule for Healthy Habits

5 servings of fruits & vegetables daily
2 hours or less of screen time
1 hour or more of physical activity
0 sugary drinks

⭐ Pharmacotherapy (e.g., Orlistat for >12 yrs) is considered for BMI >95th percentile if lifestyle changes fail after 6-12 months. Bariatric surgery is reserved for severe adolescent obesity (BMI >40 or >35 with comorbidities).

High‑Yield Points - ⚡ Biggest Takeaways

Childhood obesity is defined as a BMI ≥ 95th percentile for age and sex; overweight is BMI ≥ 85th percentile.

Universal screening is recommended starting from 2 years of age.

The most common cause is exogenous obesity (simple obesity) from caloric imbalance.

Key complications include Type 2 Diabetes, hypertension, dyslipidemia, NAFLD, and slipped capital femoral epiphysis (SCFE).

Consider syndromic causes like Prader-Willi or Bardet-Biedl syndrome with associated features.

Lifestyle modification is the cornerstone of management.

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