If you’re preparing for the United States Medical Licensing Examination® (USMLE®) Step 2 exam, you might want to know which questions are most often missed by test-prep takers. Check out this example from Kaplan Medical, and read an expert explanation of the answer. Also check out all posts in this series.
This month’s stumper
A 6-year-old boy with a history of deafness presents to the emergency department after collapsing at home. He was running after one of his three siblings when he suddenly turned pale and fell to the floor. His parents dialed 911. He subsequently recovered in the ambulance. In the emergency room, he appears pale. The parents are concerned and state that the boy is not taking any medication.
There was a maternal uncle who also experienced similar episodes but died at an early age. An electrocardiogram is performed and reveals marked QT prolongation and morphologic abnormalities of the T waves. Within one minute, the patient again loses consciousness and the electrocardiogram reveals an irregular polymorphic ventricular tachycardia that appears to undulate about the isoelectric line.
What is the most likely diagnosis?
A. Jervell-Lange-Nielsen syndrome.
B. Ortner syndrome.
C. Romano-Ward syndrome.
D. Von Hippel-Lindau syndrome.
E. Wolff-Parkinson-White syndrome.
The correct answer is A.
Kaplan Medical explains why
This patient has a congenital long QT syndrome, as evidenced by the recurrent episodes of torsades de pointes at an early age (preceding QT prolongation giving way to an irregular polymorphic ventricular tachycardia that "twists" around a point on the isoelectric line). Other evidence that points toward a diagnosis of a long QT syndrome is the presence of a maternal uncle who presented in a similar way but died at an early age. The patient has Jervell-Lange-Nielsen syndrome (JLNS) because he also has a history of deafness. A variety of congenital long QT syndromes have been identified. Jervell-Lange-Nielsen is a condition associated with sensorineural deafness.
Why the other answers are wrong
Choice B: Ortner syndrome is incorrect. Ortner syndrome is recurrent laryngeal nerve palsy caused by a large left atrium associated with mitral stenosis.
Choice C: Romano-Ward syndrome (RWS) does not have deafness. The two used to be distinguished as autosomal recessive versus autosomal dominant, respectively; however, that is no longer used. There are 10 known types based on the genetic locus, the types of protein that is produced and the ion channel affected. JLNS is seen with homozygous mutations of two specific genes, whereas RWS is heterozygous.
Attacks of torsades de pointes in the congenital syndromes are commonly associated with sympathetic stimulation such as exercise, wakening, or fright. Some occur during sleep. Paroxysms may produce syncope, which, if prolonged, may be complicated by seizures. For this reason, the syndrome may often be misdiagnosed as epilepsy.
Specific mutations in genes encoding for the sodium, potassium, or calcium channels in the cardiac cell have been identified in patients with congenital long QT syndromes. Delayed closure of the sodium channel results in prolongation of inward current, whereas potassium channel mutations result in delayed repolarization.
Both mechanisms result in prolongation of the QTc interval (the corrected QT interval to account for changes in heart rate = QT interval divided by the square root of the previous RR interval) and increased predisposition to early after-depolarizations. Attacks of syncope in the congenital long QT syndrome are effectively treated with high-dose beta-blockade. If this is unsuccessful, selective high left stellate ganglionectomy has been employed successfully. Occasionally, pacemaker or defibrillator implantation is necessary for resistant cases.
The prognosis of untreated congenital long QT syndrome is poor, with a high incidence of sudden death in childhood. Retrospective data indicate that the 15-year survival in patients after their first episode of torsades de pointes improved from 50% in untreated cases to 90% after treatment with beta-blockade and/or left stellate ganglionectomy.
Choice D: Von Hippel-Lindau syndrome is incorrect. This syndrome is a predisposition to renal cysts/carcinomas, pheochromocytoma, and hemangioblastoma (in lateral lobes of the cerebellum) with or without aneurysms and tortuousities of the retinal vessels, leading to subretinal hemorrhages. It presents in young adults with headache, dizziness, unilateral ataxia, or blindness.
Choice E: Wolff-Parkinson-White syndrome is incorrect. This involves a congenital accessory conduction pathway between atrium and ventricle. ECG shows rapid conduction down the accessory pathway (short PR interval) followed by initially slow depolarization through the ventricle (slurred upstroke or "delta wave" into the QRS complex).
Tips to remember
Suspect Jervell-Lange-Nielsen syndrome with:
- Prolonged QTc interval, predisposing to malignant ventricular arrhythmias (i.e., torsades de pointes and ventricular fibrillation).
- Sensorineural deafness.
- Family history.
For more prep questions on USMLE Steps 1, 2 and 3, view other posts in this series.
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