Free USMLE Step 2 CK Pediatrics practice questions

This teenager has juvenile myoclonic epilepsy (JME): onset at 12 to 18 years with myoclonic jerks of the arms shortly after waking, a generalized tonic-clonic seizure after sleep loss, a normal examination, and generalized 4 to 6 Hz polyspike-and-wave with photosensitivity. She has appropriately been started on lamotrigine (rather than valproate, which is teratogenic) plus folic acid.

The strongest modifiable triggers in JME are sleep deprivation, alcohol, and, in photosensitive patients, flashing lights. Myoclonus and convulsions cluster after short nights and early awakening, so the most useful self-management advice for a student planning all-nighters is a regular sleep-wake schedule with adequate sleep, together with limiting alcohol and taking medication consistently. These measures reduce breakthrough seizures alongside drug therapy.

B. Avoiding aerobic exercise and sports is unnecessary; physical activity does not provoke JME, and patients are encouraged to exercise with ordinary water and height safety precautions.

C. The ketogenic diet is reserved for drug-resistant epilepsies such as Lennox-Gastaut syndrome or GLUT1 deficiency, not for a teen controlled on one drug.

D. Moderate caffeine is not an established JME trigger; eliminating it is far less important than protecting sleep.

E. Planning to stop lamotrigine after 2 seizure-free years is wrong because JME is usually lifelong and relapse after withdrawal is common, unlike childhood absence epilepsy or self-limited epilepsy with centrotemporal spikes.

Syncope during exertion is cardiac until proven otherwise and, in a young athlete, points to a fixed or dynamic outflow obstruction or an arrhythmia. This boy has several red flags: syncope while sprinting, exertional dyspnea, and a family history of sudden death at a young age. The murmur is the clincher: a systolic ejection murmur that increases with Valsalva (which reduces preload and LV size, worsening the obstruction) and decreases with squatting (which increases preload and afterload) is characteristic of hypertrophic cardiomyopathy with LV outflow tract obstruction. His ECG supports the diagnosis with LVH voltage and deep, narrow septal Q waves in the lateral leads.

The next step is transthoracic echocardiography, which shows asymmetric septal hypertrophy, systolic anterior motion of the mitral valve and the outflow gradient. Cardiac MRI, ambulatory monitoring, genetic testing and family screening follow, and he must refrain from competitive sports pending specialist evaluation. HCM is a leading cause of sudden cardiac death in young athletes, and exertional syncope is a major risk marker for ICD consideration.

A. Holter monitoring may detect nonsustained VT later in risk stratification but does not establish the structural diagnosis suggested by the murmur. B. Tilt-table testing evaluates recurrent unexplained reflex syncope; exertional syncope with a murmur is not reflex syncope. C. EEG is low yield without features of seizure; he recovered quickly without confusion. E. Exercise testing can be part of HCM risk assessment once the anatomy is known, but exercising a patient with unexplained exertional syncope and a suspected outflow obstruction before imaging is unsafe.

A first episode of wheeze in an infant under 2 years, after a few days of rhinorrhea and cough, during winter, with a sick sibling, tachypnea, retractions, and diffuse crackles and wheezes, is bronchiolitis, most often caused by RSV. The AAP guideline states that bronchiolitis is a clinical diagnosis based on history and examination, and that clinicians should not routinely obtain radiographs or laboratory studies, including viral testing, in a typical case. Tests rarely change management, and they often lead to unnecessary antibiotics.

What matters is assessing severity and risk: age under 12 weeks, prematurity, hemodynamically significant heart disease, chronic lung disease, or immunodeficiency; hydration; work of breathing; and oxygen saturation. This infant is older than 12 weeks, born at term, feeding adequately, and has an SpO2 above 90% after suctioning, so care is supportive (nasal suctioning, hydration, oxygen only if SpO2 falls below 90%), with return precautions or brief observation. Albuterol, corticosteroids, and antibiotics are not recommended.

A. A chest radiograph often shows hyperinflation and patchy atelectasis that is misread as pneumonia, leading to antibiotics. It is reserved for an atypical course, focal findings, or severe disease needing intensive care.

B. A complete blood count and blood culture are not indicated in a well-appearing infant older than 2 to 3 months with typical bronchiolitis and low-grade fever; the risk of bacteremia is very low.

C. Identifying the virus does not change management in a typical case; testing is used mainly for infection control cohorting or research.

D. A blood gas is reserved for severe distress or suspected respiratory failure, which she does not have.

This boy has hypogonadotropic hypogonadism (low LH, FSH and testosterone) with lifelong anosmia and absent olfactory bulbs on MRI: Kallmann syndrome. GnRH neurons originate in the olfactory placode and migrate with the olfactory nerves to the hypothalamus during fetal life; genetic defects (for example ANOS1, FGFR1) disrupt both migrations, producing GnRH deficiency and anosmia together. Because GnRH deficiency begins in fetal life, there is little fetal testosterone action late in gestation, which explains his micropenis and history of cryptorchidism, findings that point away from simple constitutional delay. Height is often normal because growth hormone is intact, and the growth plates stay open, giving eunuchoid proportions later. Treatment is testosterone to induce puberty, with gonadotropin therapy (hCG plus FSH) later to induce spermatogenesis when fertility is desired.

A. Constitutional delay is the most common cause of delayed puberty and also has low gonadotropins, but it does not cause anosmia, micropenis or absent olfactory bulbs; distinguishing the two can otherwise be difficult. B. Klinefelter syndrome is primary testicular failure with high LH and FSH, and puberty usually starts normally. C. A prolactinoma suppresses gonadotropins, but the prolactin level and pituitary are normal. D. Craniopharyngioma causes hypogonadotropic hypogonadism with headache, visual field loss, growth failure and often other pituitary deficiencies; the visual fields, growth, IGF-1 and pituitary imaging are normal here.

Each unit of red cells adds about 200 to 250 mg of iron that the body cannot excrete, so chronically transfused patients depend on chelation. This adolescent has been poorly adherent and now has severe iron overload in several organs: very high ferritin and liver iron, hypogonadotropic hypogonadism with delayed puberty, short stature and skin pigmentation. Most important, her cardiac MRI T2* is 7 ms; values below 20 ms indicate myocardial iron and below 10 ms indicate severe loading, which predicts a high near-term risk of heart failure even though her ejection fraction is still normal. Iron cardiomyopathy, with heart failure and arrhythmias, remains the leading cause of death in transfusion-dependent thalassemia.

Myocardial iron can accumulate before ventricular function declines, which is why T2* is monitored rather than relying on ferritin or echocardiography. With a T2* below 10 ms, therapy is intensified, typically with combined deferoxamine and deferiprone or high-dose deferoxamine, and adherence barriers are addressed. Overt cardiac decompensation calls for continuous intravenous deferoxamine plus deferiprone.

A. Hepatocellular carcinoma is a real long-term risk of hepatic iron and cirrhosis, but it develops over many years and is a less frequent cause of death. B. Sepsis is a major risk after splenectomy and with deferoxamine-associated Yersinia, but she has neither, and it is not the leading cause of death. D. Iron-related diabetes can develop, but ketoacidosis is uncommon in this setting. E. Thrombosis risk rises mainly after splenectomy and in non-transfusion-dependent disease; it is not her dominant threat.

Stimulants, combined with behavioral supports, are first-line treatment for school-age children with ADHD, and routine ECG screening is not required for healthy children. However, before starting any ADHD medication, the clinician must take a targeted cardiac history: syncope or chest pain with exertion, palpitations, known heart disease, and a family history of sudden or unexplained death before age 50, cardiomyopathy, long QT syndrome, or other inherited arrhythmias. A positive answer calls for an ECG and cardiology evaluation before medication.

This boy has two red flags together: exertional syncope and a young relative with unexplained sudden death during exercise. That combination raises concern for hypertrophic cardiomyopathy, long QT syndrome, catecholaminergic polymorphic ventricular tachycardia, or another inherited arrhythmia syndrome. Exertional syncope warrants a cardiac workup regardless of the ADHD plan, and stimulants raise heart rate and blood pressure. A normal physical examination does not exclude these conditions. Once a cardiac cause is excluded, a stimulant can usually be started.

A. Starting methylphenidate now skips an evaluation that is mandatory with these red flags; blood pressure checks do not detect channelopathies or cardiomyopathy. B. Atomoxetine also raises heart rate and blood pressure and carries the same cardiac precautions, so it does not remove the need for evaluation. C. Guanfacine is a reasonable non-stimulant, but it can cause bradycardia and hypotension, and choosing it does not address the unexplained exertional syncope. D. Delaying all medication for years withholds effective treatment from an impaired child, when a prompt cardiac evaluation would answer the safety question.

Distinguishing sinus tachycardia from SVT is a key bedside decision, because the treatments are opposite: sinus tachycardia is treated by fixing its cause (here, fluid resuscitation and antipyretics), while adenosine or cardioversion would be useless or harmful. Features favoring sinus tachycardia are a clear precipitant (fever and dehydration from gastroenteritis with signs of compensated hypovolemic shock), a rate below about 220/min in an infant, beat-to-beat variability with crying, activity, and comforting, a gradual onset, and normal P waves (upright in I and aVF, with a normal PR interval) before every QRS. SVT in infants usually has a rate above 220/min that is fixed and does not change with activity, absent or retrograde P waves, an abrupt start and stop, and often a vague history of poor feeding. Her rate should fall as her volume deficit and fever are corrected, which also confirms the diagnosis.

A. Atrioventricular reentrant tachycardia, the most common infant SVT, has a fixed rate, usually above 220/min, and no visible or retrograde P waves. B. Atrial flutter, most often seen in fetuses and newborns, shows sawtooth flutter waves with a fixed atrial rate and often variable conduction. D. Ventricular tachycardia produces wide QRS complexes with AV dissociation. E. Ectopic atrial tachycardia can show P waves before each QRS, but they have an abnormal axis or morphology, and the rate is incessant and does not track the child's state; a normal P-wave axis with an obvious physiologic trigger points to sinus tachycardia.

Since the 2023 to 2024 season, ACIP and the AAP have stated that egg allergy of any severity, including anaphylaxis, is not a contraindication or a precaution for influenza vaccination. Any licensed, age-appropriate influenza vaccine (egg-based or egg-free) may be given, and no additional safety measures beyond those recommended for every vaccine are needed. The amount of ovalbumin in current egg-based vaccines is minute, and large studies of egg-allergic children, including those with prior anaphylaxis, have shown no increase in serious reactions. Routine precautions mean that any vaccine is given in a setting prepared to recognize and treat anaphylaxis. This boy has also tolerated prior influenza vaccines, which further supports routine administration. His asthma is an additional reason he should be vaccinated every year, because children with asthma are at higher risk of influenza complications. Because of his asthma, an injectable vaccine is preferred over the intranasal live vaccine (asthma is a precaution for LAIV at age 5 and older), but his egg allergy does not restrict the choice of product.

A. Vaccine skin testing before influenza vaccination is no longer recommended for egg allergy and only delays protection. B. Graded (split) dosing was an older strategy that is unnecessary and adds a second injection. C. Restricting him to egg-free vaccines in a hospital is outdated guidance that was removed from the recommendations; egg-free vaccines are acceptable but not required, and the setting is the same as for any vaccine. E. Withholding vaccination and relying on antiviral prophylaxis leaves a child with asthma unprotected for the season; chemoprophylaxis is not a substitute for vaccination.