QUESTION: 57

A22-year-old male presents to an acute care clinic in order to have two genital lesions evaluated. He first noticed the lesions about 2 weeks ago, but delayed seeking medical care because he believed they were harmless due to the lack of any discomfort. He states that he does engage in unprotected sexual intercourse, with the most recent time being 1 month ago. On examination, the glans penis features two distinct nontender papules with elevated edges surrounding ulcerated craters. They each measure 1 cm in diameter. There is also nontender bilateral inguinal lymphadenopathy.

The drug of choice for treating this patient works by which of the following mechanisms?

interfering with protein synthesis at the ribosome
attaching to sterols in cell membranes
inhibiting bacterial cell wall synthesis
inhibiting the transport of amino acids into bacteria
inhibiting dihydrofolate reductase

Answer(s): C

Explanation:

This patient's presentation is consistent with primary syphilis. Primary syphilis manifests itself usually in the form of solitary or multiple raised, firm papules which eventually erode to form ulcerative craters with raised, indurated margins surrounding the centralized ulcer. These lesions, called chancres, most commonly involve the glans penis in males and the vulva or cervix in females, although they may appear rarely in other areas. Syphilis is caused by the spirochete, T. pallidum, which can be visualized by darkfield microscopy, by silver stain, or by fluorescent antibody microscopy. There is an incubation period of approximately 3 weeks separating the time of initial exposure to T. pallidum and the time of chancre formation. Syphilis is characterized by the presence of latent stages in which there are no signs of clinical disease present. Penicillin is the drug of choice for the treatment of syphilis. In addition to treating patients with diagnosed syphilis, it is recommended that treatment also be administered to all sexual contacts of the past 90 days. It has been demonstrated that up to 30% of asymptomatic sexual contacts of patients with infectious lesions within the past 30 days go on to develop syphilis if left untreated. If left untreated, patients may ultimately develop tertiary syphilis characterized by significant destructive neurologic and cardiovascular symptoms. The mortality rate for untreated tertiary syphilis is approximately 20%.

Cephalosporins and penicillin antibiotics act by interfering with the late stages of bacterial cell wall synthesis, although the precise biochemical reactions are not entirely understood. Peptidoglycan provides mechanical stability to the cell wall because of its high degree of cross-linking with alternating amino pyranoside sugar residues (N-acetylglucosamine and N-acetylmuramic acid). The completion of the cross- linking occurs by the action of the enzyme transpeptidase. This transpeptidase reaction, in which the terminal glycine residue of the pentaglycine bridge is joined to the fourth residue of the pentapeptide (D- alanine) thereby releasing the fifth residue (D-alanine), is inhibited by beta- lactams.

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QUESTION: 58

A22-year-old male presents to an acute care clinic in order to have two genital lesions evaluated. He first noticed the lesions about 2 weeks ago, but delayed seeking medical care because he believed they were harmless due to the lack of any discomfort. He states that he does engage in unprotected sexual intercourse, with the most recent time being 1 month ago. On examination, the glans penis features two distinct nontender papules with elevated edges surrounding ulcerated craters. They each measure 1 cm in diameter. There is also nontender bilateral inguinal lymphadenopathy. Six hours after treating this patient, he calls your office with complaints of new-onset headache, myalgia, and malaise. He also states that he felt feverish immediately prior to calling and measured his temperature, which was 99.8°F. Which of th e following is most appropriate at this time?

Advise transport to the nearest ED for immediate evaluation.
Advise use of acetaminophen and provide reassurance.
Advise immediate use of Benadryl and then have the patient go to the nearest ED.
Start treatment with levaquin.
Start treatment with oral corticosteroids.

Answer(s): B

Explanation:

This patient's presentation is consistent with primary syphilis. Primary syphilis manifests itself usually in the form of solitary or multiple raised, firm papules which eventually erode to form ulcerative craters with raised, indurated margins surrounding the centralized ulcer. These lesions, called chancres, most commonly involve the glans penis in males and the vulva or cervix in females, although they may appear rarely in other areas. Syphilis is caused by the spirochete, T. pallidum, which can be visualized by darkfield microscopy, by silver stain, or by fluorescent antibody microscopy. There is an incubation period of approximately 3 weeks separating the time of initial exposure to T. pallidum and the time of chancre formation. Syphilis is characterized by the presence of latent stages in which there are no signs of clinical disease present. Penicillin is the drug of choice for the treatment of syphilis. In addition to treating patients with diagnosed syphilis, it is recommended that treatment also be administered to all sexual contacts of the past 90 days. It has been demonstrated that up to 30% of asymptomatic sexual contacts of patients with infectious lesions within the past 30 days go on to develop syphilis if left untreated. If left untreated, patients may ultimately develop tertiary syphilis characterized by significant destructive neurologic and cardiovascular symptoms. The mortality rate for untreated tertiary syphilis is approximately 20%.

Cephalosporins and penicillin antibiotics act by interfering with the late stages of bacterial cell wall synthesis, although the precise biochemical reactions are not entirely understood. Peptidoglycan provides mechanical stability to the cell wall because of its high degree of cross-linking with alternating amino pyranoside sugar residues (N-acetylglucosamine and N-acetylmuramic acid). The completion of the cross- linking occurs by the action of the enzyme transpeptidase. This transpeptidase reaction, in which the terminal glycine residue of the pentaglycine bridge is joined to the fourth residue of the pentapeptide (D- alanine) thereby releasing the fifth residue (D-alanine), is inhibited by beta- lactams.

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QUESTION: 59

A 26-year-old HIV-positive man is admitted to the hospital for treatment of a varicella-zoster infection. On the fourth day of treatment, he develops an acute renal insufficiency. What is the most likely treatment- related mechanism accounting for the patient's acute renal insufficiency?

the formation of toxic metabolites
decreased glomerular filtration rate
the precipitation of acyclovir in renal tubules
direct tubular cytotoxic injury
hypersensitivity interstitial nephritis

Answer(s): C

Explanation:

HIV-positive patients who develop a varicella-zoster infection require aggressive antibiotic therapy. Intravenous acyclovir should be adminstered for a period of 7 days, and oral maintenance therapy should be started for secondary prophylaxis. While acyclovir is usually well tolerated, it can be nephrotoxic when given intravenously. It may crystallize within renal tubules and cause subsequent acute tubular necrosis. Acyclovir is more likely to cause nephrotoxic effects if there is associated dehydration or a preexisting renal insufficiency. Individuals who have a preexisting renal insufficiency should have the dose and frequency of acyclovir administration adjusted according to their baseline creatinine clearance.

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QUESTION: 60

A 34-year-old amateur spelunker develops cough, dyspnea, and fever 2 weeks after a caving expedition to caves in Kentucky. On physical examination, the patient's temperature is 102°F and respiratory rate is 24. On pulmonary examination, there are diffuse crackles bilaterally. A CXR is shown in Figure

.

Which of the following is the most likely cause of disease in this patient?

The patient likely developed influenza from close contact with the other members of the caving expedition.
The patient likely has disseminated aspergillosis.
The patient likely has miliary tuberculosis.
The patient likely has acute pulmonary histoplasmosis.
The patient likely has Pneumocystis jiroveci pneumonia.

Answer(s): D

Explanation:

The patient has diffuse interstitial infiltrates on CXR that correspond in time and presentation to acute inhalation histoplasmosis. This would be seen in a patient, such as an amateur spelunker, who has been in a cave with bats. It is the act of crawling through the cave that disturbs the spores of histoplasmosis that grow in the bat guano. The incubation period for influenza is 12 days. It is passed primarily by secretions from the nose spread by hands. The other members of the expedition were not sick, as they might be with influenza. Disseminated aspergillosis occurs in immunocompromised patients who have defects in both cell-mediated and humoral immunity. This patient does not have this. While the CXR could mimic military tuberculosis, the association with caving 14 days before would make tuberculosis less likely and histoplasmosis more likely. There is no history that the patient is immunocompromised with HIV and would be at risk for P. jiroveci pneumonia. Fungal serologies would establish the diagnosis, but acute and convalescent serologies would take 3 weeks for results. These are only useful in outbreak investigations. The other choices do not fit due to the reasons above. Treatment of acute respiratory histoplasmosis is based on severe hypoxia and would require arterial blood gases to establish the need for therapy. None of the fungal infections mentioned are transmissible person to person, therefore respiratory isolation would not be necessary. Histoplasmosis is a dimorphic fungus that grows as a yeast at body temperature and a mold at room temperature. The mold produces the spores that are infectious. A similar situation occurs for Cryptococcus neoformans. C. immitis and aspergillosis are not transmitted from person to person.

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