Repeated USMLE Questions Step 1- 379

Q- A young boy presents with multiple skin lesions for more than a year. He is sensitive to sun and biopsies of some of his lesions show squamous cell carcinoma. Which of the following mutations is most likely present in this condition?

A- Missense mutation

B- Nonsense mutation

C- Point mutation

D- Thymidine dimers

D- Thymidine dimers- This is most likely a case of xeroderma pigmentosa. It is an autosomal recessive disease characterized by defect in excision repair. Ultraviolet light exposure leads to the formation of thymidine dimers which are not repaired due to this mutation.

Q- Which one of the following antibiotics is the most appropriate treatment of chancroid, a bacterial infection caused by Haemophilus ducreyi?

A- Ampicillin

B- Ceftriaxone

C- Ciprofloxacin

D- Vancomycin

B- Ceftriaxone- It is the treatment of choice for this condition. It is given as one time intramuscular injection. Another alternative is azithromycin.

Q- A patient with a recent history of meningitis develops headache, blurred vision and cognitive decline. CT scan shows enlarged ventricles. Which of the following is most likely responsible for this condition?

A- Destruction of the gray matter

B- Excessive CSF production

C- Impaired CSF resorption

D- Obstruction of cerebral aqueduct

C- Impaired CSF resorption- Meningitis can cause scarring of the arachnoid granulations, which are responsible for returning fluid from the CSF into circulation, leads to failure to resorb adequate CSF.

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