Three USMLE Step 1 questions on insulin types, a genetic tumor syndrome and a classic toxicology sign. Pick your answer first, then open the explanation.
Question 1: Which insulin is rapid-acting?
A 12-year-old boy is diagnosed with type 1 diabetes and started on insulin. Which one of the following is a rapid-acting insulin?
A. Aspart B. Detemir C. Glargine D. NPH
Correct answer: A. Aspart
Insulin aspart (like lispro and glulisine) is a rapid-acting insulin. It starts working in about 15 minutes, peaks at 1–2 hours and lasts 3–5 hours, so it is given with meals.
Why the other options are wrong:
Detemir and glargine are long-acting basal insulins lasting about 20–24 hours with no real peak.
NPH is intermediate-acting, lasting about 10–16 hours.
High-yield: Regular insulin is the short-acting insulin given IV for diabetic ketoacidosis and hyperkalemia.
Question 2: Bilateral acoustic schwannomas and juvenile cataract
Bilateral acoustic schwannomas and juvenile cataracts occur in which one of the following conditions?
A. Marfan syndrome B. Neurofibromatosis type 1 C. Neurofibromatosis type 2 D. Sarcoidosis
Correct answer: C. Neurofibromatosis type 2
Neurofibromatosis type 2 is autosomal dominant, caused by a mutation in the NF2 tumor suppressor gene (merlin) on chromosome 22. It causes bilateral vestibular (acoustic) schwannomas, meningiomas, ependymomas and juvenile cataracts.
Why the other options are wrong:
Marfan syndrome (FBN1, chromosome 15) causes lens dislocation, tall stature and aortic dissection, not schwannomas.
A Burton line, a bluish line on the gingiva, occurs in which one of the following conditions?
A. Acetaminophen overdose B. Lead poisoning C. Mercury poisoning D. Nicotine toxicity
Correct answer: B. Lead poisoning
Lead poisoning causes the Burton (lead) line on the gums. Other features: basophilic stippling of red cells, microcytic sideroblastic anemia (lead inhibits ferrochelatase and ALA dehydratase), abdominal colic, wrist and foot drop, and encephalopathy in children.
Mercury poisoning causes tremor, erethism (irritability, shyness) and kidney damage.
Nicotine toxicity causes nausea, vomiting, salivation and tachycardia, not gum lines.
High-yield: On X-ray, lead also causes dense “lead lines” at the metaphyses of long bones in children. Treat with succimer (children), or dimercaprol and EDTA for severe poisoning.
