Question 251
A 37-year-old male presents to the emergency room complaining of fever, chills, malaise, and a non-productive cough that has developed over five days. A chest x-ray reveals patchy infiltrates. His disease process is illustrated in the image below. Of the following, what was the most likely etiology for his infection?
A. Hiking in California
B. Inadequate childhood vaccination
C. Working at tuberculosis clinic
D. Intravenous drug use
E. Unprotected sexual contact
Answer for Question 251
Answer: A (Hiking in California).
Explanation: The lesion is a spherule (yellow arrow) filled with endospores (blue arrows) and is the typical histologic appearance of Coccidioides immitis, which is the dimorphic fungus found in the San Juaquin Valley area in California and Arizona. Immunocompetent individuals can be asymptomatic or they can present acutely with a respiratory type condition, or they can present insidiously.
Question 252
A 56-year-old black female over the past year has developed stiffness of her hands and when she goes outside in the cold, she often develops white discoloration of the distal third of her fingers and sometimes an accompanying blue discoloration of the distal tips of the fingers. She is referred to a rheumatologist who performs a punch biopsy of the skin, which is illustrated below. Of the following, the antibody responsible for her condition is directed against which substance?
A. Ro/SS-A
B. Cyclic citrullinated peptides
C. Double-stranded DNA
D. Smith antigen
E. DNA topoisomerase I
Answer for Question 252
Answer: E (DNA topoisomerase I)
Explanation: The patient has features of localized scleroderma (involving the skin)–the white and blue discoloration of the fingers is Raynaud phenomenon. The antibody often associated with scleroderma is anti-scl70, which is against DNA topoisomerase I. Anti-Ro/SS-A is found in Sjogren syndrome and antibodies against cyclic citrullinated peptides are found in rheumatoid arthritis. Antibodies against double-stranded DNA and Smith antigen are more characteristic of systemic lupus erythematosus.
The histologic features of localized scleroderma are fibrosis of the dermis, loss of rete pegs and loss of skin appendage. A trichrome stain would highlight the fibrosis (the black arrow is just representative of an area of fibrosis, most of the dermis in the section is fibrotic).
Question 253
A 41-year-old immunocompetent male develops fever, chills, some mild shortness of breath, and a non-productive cough and goes to an acute care clinic. The doctor has a chest x-ray performed, which reveals patchy infiltrates of the lungs. The image below illustrates the organism causing his infection. During his examination, the doctor asks about recent travel, and he states that he recently got back from a hiking trip. Of the following, which state did he most likely visit?
A. Washington
B. California
C. Montana
D. Michigan
E. New Mexico
Answer for Question 253
Answer: D (Michigan)
Explanation: Blue arrows indicate the characteristic histologic features of Blastomyces dermatitidis–a broad-based budding yeast. The fungus has a thick, double-contoured wall (both of which would distinguish it from Histoplasma capsulatum). Like Histoplasma, Blastomyces is associated with the Ohio-Mississippi River valleys, but also the northern midwest, upstate New York, and southern Canada (all locations around the Great Lakes.)
Question 254
A researcher is studying acute inflammation in mice as a model for humans. Assuming the same mediators are present, of the following, which is most directly responsible for the position of the cells at the star?
A. P-selectin
B. ICAM-1
C. CD20
D. CD31
E. Eotaxin
F. Neutrotaxin
Answer for Question 254
Answer: D (CD31)
Explanation: The cells at the star are neutrophils (not eosinophils) and they are outside the vessel. The most important mediator in the list is CD31 (PECAM-1), which allows transmigration of the neutrophil out of the vessel. P-selection and ICAM-1 would play a role in getting the neutrophil to be adherent to the wall, but not in moving through it. A similar question to this one is included in the NBME’s sample question group (available from their website).
Question 255
A forensic pathologist is testifying in court regarding an alleged homicide, in which a woman was beaten by a man and later died. At the time of autopsy, he took sections of the skin from the injuries and a section from the most vital injury in the court case is illustrated below. If asked to give an approximation of the time lapsed between the injury and death, of the following, which would be the best response?
A. Immediate
B. Around 30 minutes
C. Around 12 hours
D. Around 6 days
E. Around two weeks
Answer for Question 255
Answer: C (Around 12 hours).
Explanation: The cells surrounding the blood vessel (yellow arrows) are neutrophils (with a few eosinophils also present). In the inflammatory response, neutrophils are most common around 6-24 hours; at around 1-2 days or more, macrophages start being found.
