WBR0536

Author	[[PageAuthor::Yazan Daaboul, M.D. (Reviewed by Alison Leibowitz) (Reviewed by Serge Korjian)]]
Exam Type	ExamType::USMLE Step 1
Main Category	MainCategory::Pharmacology
Sub Category	SubCategory::Neurology
Prompt	[[Prompt::A 10-year-old boy is brought to the pediatrician's office for declining school performance and poor concentration. The mother explains that her child is a day dreamer and is concerned about his recurrent blank stares. She is fearful that her son has attention deficit disorder (ADD). Following an extensive work-up, the patient is diagnosed with seizure disorder and treatment is initiated. Which of the following mechanisms of action corresponds to the medication prescribed to this patient?]]
Answer A	AnswerA::Inactivation of dopamine receptors
Answer A Explanation	AnswerAExp::Antipsychotics used to treat psychiatric diseases such as schizophrenia act by inactivation of dopamine receptors.
Answer B	AnswerB::Inactivation of sodium channels
Answer B Explanation	AnswerBExp::Phenytoin's mechanism of action is the inactivation of sodium channels. Although phenytoin is not commonly administered to treat absence seizures, it is used in tonic-clonic generalized seizures and partial seizures.
Answer C	AnswerC::Activation of GABA receptors
Answer C Explanation	AnswerCExp::Topiramate activates GABA receptors. It is not commonly administered to treat absence seizures, but is effective in treating partial and tonic-clonic generalized seizures.
Answer D	AnswerD::Inactivation of thalamic T-type calcium channels
Answer D Explanation	AnswerDExp::Ethosuxamide, the first line treatment for absence seizures, is a thalamic T-type calcium channel blocker.
Answer E	AnswerE::Inhibition of GABA reuptake
Answer E Explanation	AnswerEExp::Tiagabine, which acts by inhibition of GABA reuptake, is effective in partial seizures, but is not usually used to treat absence seizures.
Right Answer	RightAnswer::D
Explanation	[[Explanation::Absence seizures are described as episodes of succint lapse of consciousness or “blanking out”. Simple absence seizures are often very short in duration that they may be undetectable without electroencephalography (EEG) and may be easily confused with daydreaming or lack attention and concentration. Absence seizures do not have a post-ictal phase; patients usually continue the same activities they were performing prior to the seizure onset. Absence epilepsy (recurrent absence seizures) occurs most commonly among children aged 4-15 years. The EEG classically shows 3-Hz spike-and-slow-wave complexes after a seizure is triggered by hyperventilation. Ethosuximide, a succinimide antiepileptic drug, is the first line treatment for absence seizure (petit mal). It is a low voltage-activated thalamic T-type calcium channel blocker. Ethosuximide has a rare frequency of adverse drug reactions. The most common side effects include GI distress, fatigue, and headache. Valproic acid may also be used to treat absence seizures as second line therapy. Educational Objective: Ethosuxamide, the first line treatment for absence seizures, is a thalamic T-type calcium channel blocker. References: Glauser TA, Cnaan A, Shinnar S, et al. Ethosuximide, valproic acid, and lamotrigine in childhood absence epilepsy. N Engl J Med. 2010;362(9):790-9.]]
Approved	Approved::Yes
Keyword	WBRKeyword::Absence seizure, WBRKeyword::Seizure, WBRKeyword::Petit mal, WBRKeyword::Ethosuximide, WBRKeyword::Calcium channel blocker, WBRKeyword::T-type, WBRKeyword::Mechanism of action, WBRKeyword::Neurological
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