Micro USMLE 8-28(11) (qmax 8/23 - 6-40)

Question 1

This HIV-positive patient’s severe upper back pain and low CD4 count, together with a finding of caseating granulomas (necrotic inflammatory infiltrate and giant cells) on a bone biopsy specimen, suggest that he has extrapulmonary tuberculosis of the spine, also known as Pott disease. The classic clinical presentation includes spinal pain, kyphosis due to compromised vertebral integrity , and neurologic signs ranging from radicular pain to cord compression and paralysis. The most common sites for Pott disease are the lower thoracic and upper lumbar spine.

Like pulmonary tuberculosis, Pott disease is treated with a combination of antimycobacterial therapy, often consisting of?

Answer 1

isoniazid, rifampin, and pyrazinamide. Rifabutin is sometimes used in place of rifampin in HIV-positive patients who are receiving antiretroviral therapy. Ideally, this patient would also begin taking antiretroviral drugs.

It is important to note that individuals with Pott disease may or may not show symptoms of pulmonary tuberculosis at the time they present with back pain. Also, a negative purified protein derivative test result, as seen in this patient, is insufficient to rule out tuberculosis (pulmonary or extrapulmonary) in a patient with advanced HIV infection. This is because the suppression of CD4+ cells by HIV infection can result in anergy toward the tuberculin antigen.

Question 2

Combination chemotherapy with vincristine, doxorubicin, and dexamethasone would be warranted for multiple myeloma of the spine. Although this patient does have recent-onset back pain and lytic lesions on imaging, the caseating necrosis on the bone biopsy specimen—in the context of advanced HIV infection—is more consistent with Pott disease. Intravenous amphotericin is a potent antifungal medication. Fungal infections are more common with HIV, but this patient’s caseating necrosis on a biopsy specimen is more consistent with ?

Answer 2

Pott disease. Intravenous vancomycin is appropriate treatment for coverage of methicillin-resistant Staphylococcus aureus (MRSA), which can cause epidural abscesses, but this patient’s pathogen is tuberculosis based on biopsy findings. Highly active antiretroviral therapy (HAART) should be recommended for this patient but will not treat the immediate cause of his back pain.

Question 3

Pott disease, also called tuberculosis of the spine, classically manifests with back pain, kyphosis, and neurologic signs. Like pulmonary tuberculosis, it is treated with?

Answer 3

combination antimycobacterial therapy: isoniazid, rifampin (or rifabutin), and pyrazinamide.

Question 4

This 12-year-old girl had a self-limiting episode of sore throat 1 month ago and presents with joint pain. Aschoff nodules (interstitial myocardial granulomas) are seen in the tissue biopsy specimen. These findings indicate a diagnosis of rheumatic fever (RF), which is caused by group A streptococci.
RF may result in acute holosystolic mitral regurgitation, but years after a bout of rheumatic fever, calcification of warty vegetations may cause mitral valve stenosis . In its mild form, mitral valve stenosis may cause a mid-diastolic opening snap followed by ?

Answer 4

a low-pitched murmur heard best at the apex. In the United States, the incidence of mitral valve stenosis secondary to rheumatic fever is low, given the widespread use of antibiotics. However, rheumatic mitral valve stenosis is prevalent in immigrant populations.

Question 5

A friction rub heard throughout the precordium is associated with pericarditis.
A harsh crescendo-decrescendo early systolic murmur heard at the right upper sternal border with radiation to the carotids indicates aortic stenosis. It can be caused by?

Answer 5

RF, but the aortic valve is not the most commonly affected valve.
A mid-systolic click heard best at the apex is a sign of mitral valve prolapse and would be unlikely to develop in a patient who had RF in childhood.
An S4 gallop heard best at the apex is associated with concentric left ventricular hypertrophy.

Question 6

Rheumatic heart disease, uncommon in the United States, occurs after pharyngeal infection with group A streptococci. Rheumatic heart disease affects?

Answer 6

high-pressure valves first: mitral, then aortic, and finally tricuspid valves.

Question 7

This patient presents with fever, myalgia, cough, headache, nausea, and vomiting. He has dyspnea, and a chest x-ray reveals bilateral lung infiltrates and pleural effusions, indicative of pulmonary edema. His laboratory findings show leukocytosis, thromobocytopenia, and elevated liver enzyme levels. All of these point to a diagnosis of hantavirus cardiopulmonary syndrome.

Hantavirus is in the bunyavirus family. Another bunyavirus, Crimean-Congo hemorrhagic fever, might present with similar symptoms, but it has been identified only in Africa, the Middle East, and Eastern Europe. Hantavirus is found in North, Central, and South America; infections in the United States are most commonly observed in the southwestern states of Utah, New Mexico, Colorado, and Arizona where this patient lives. In contrast with most other bunyaviruses, which are transmitted by arthropod vectors (mosquitoes, ticks, or sand flies), transmission of hantavirus occurs through contact with ?

Answer 7

rodents. Deer mice are the natural reservoir for the hantavirus, and transmission occurs through contact with their feces.

Question 8

Ticks are associated with a number of viral, bacterial, and protozoal diseases, including Lyme disease.

Bats are associated with various pathogens, including SAR-like coronavirus and rabies virus.

Mosquitoes are?

Answer 8

vectors for many infectious diseases, including malaria.

Reduviid bugs are vectors for Trypanosoma cruzi infections, which cause Chagas disease.

Question 9

Hantavirus presents with a severe, sudden onset of pulmonary edema. The virus is found in North, Central, and South America; infections in the United States are most commonly observed in?

Answer 9

the Southwest. Rodents are the natural reservoir for hantavirus; the disease is spread through contact with the feces of deer mice.

Question 10

This patient likely has a nosocomial infection related to her central venous catheter (CVC), as indicated by the change in mental status and her fever without another obvious cause.?

Answer 10

Serratia marcescens is the most likely culprit here, in light of the blood culture findings: It is a gram-negative rod that produces red pigment, like that shown in the image (think of red maraschino cherries). Unlike the other bacteria here, Serratia is a frequent cause of CVC infections rather than urinary catheter infections.

Question 11

Proteus mirabilis is a gram-negative bacillus that is a frequent cause of nosocomial urinary tract infections. It produces the enzyme urease, which serves to create a more alkaline environment for itself. The hallmark of a urease-producing organism such as ?

Answer 11

Proteus is the production of kidney stones along with infection. It does not produce pigment.

Question 12

Escherichia coli is the most common cause of urinary tract infection. It is a gram-negative rod, but it produces no pigments.

Klebsiella pneumoniae is a gram-negative rod that is responsible for approximately 8% of nosocomial infections. It is a significant cause of urinary tract infection and pneumonia in hospitalized and ambulatory patients, especially in alcoholic and diabetic ones. Klebsiella pneumoniae does not produce pigments when cultured. Clinically, Klebsiella pneumonia is associated with a mucoid, bloody sputum, sometimes referred to as “currant jelly sputum.”

Staphylococcus saprophyticus is the second most common cause of?

Answer 12

urinary tract infection in young women. It is a gram-positive coccus and does not produce any pigments.

Question 13

This patient’s CSF shows evidence of bacterial meningitis. Lumbar puncture in a patient with bacterial meningitis usually reveals increased pressure, increased white blood cells and neutrophils, high protein levels, and low glucose levels. The most common cause of bacterial meningitis is Streptococcus pneumoniae, although the incidence of infection with other organisms varies by age group:
In infants, one should suspect group B streptococci and Escherichia coli.
In children, consider S. pneumoniae, Neisseria meningitidis, and Haemophilus influenzae.
In teens and young adults (especially college-aged), the most likely cause is N. meningitidis.
In the elderly, S. pneumoniae is the most common cause.
Given the patient’s age and the most likely organism ?

Answer 13

(S. pneumoniae), ceftriaxone, a third-generation cephalosporin, is the antibiotic with the best CSF penetration and is a common choice for treatment. Ceftriaxone is also an appropriate choice for empiric treatment if the causative organism is not known.

Cephalosporins are β-lactam antibiotics that inhibit bacterial cell wall synthesis and are less sensitive to penicillinases than penicillins.

Question 14

Fluoroquinolones act by interfering with bacterial DNA gyrase during cell division. Ciprofloxacin, the most commonly prescribed fluoroquinolone in the United States, is primarily active against gram-negative bacteria. It is used to treat pseudomonal infections in patients with cystic fibrosis and other hospitalized patients.
Isoniazid is the most potent of the antituberculosis drugs and—along with other antituberculosis drugs used in combinations—is first-line therapy for tuberculosis meningitis. It inhibits the synthesis of mycolic acids, which are required components of the mycobacterial cell wall.
Nonsteroidal anti-inflammatory drugs inhibit cyclooxygenase 1 and cyclooxygenase 2 to block prostaglandin synthesis and are used for control of ?

Answer 14

inflammation and pain. However, they are not indicated to treat bacterial meningitis.
Oseltamivir is used to treat influenza A and B infections and works by blocking viral neuraminidase, which decreases the release of progeny viruses from infected cells.
Tetracyclines inhibit the 30s ribosomal subunit by preventing the attachment of aminoacyl-tRNA. Doxycycline is a tetracycline that is commonly used to treat chlamydia, mycoplasma infections, or Borrelia burgdorferi (Lyme disease).

Question 15

In bacterial meningitis, CSF contains white blood cells (particularly neutrophils), large amounts of protein, and little glucose. Bacterial meningitis is treated with?

Answer 15

a third-generation cephalosporin, usually ceftriaxone. Vancomycin is also added if there is concern that the Streptococcus pneumoniae is resistant to ceftriaxone. Ampicillin may also be added for neonates or the elderly, if infection with Listeria monocytogenes is possible.

Question 16

The patient presents with stupor, fevers, chills, vomiting, diarrhea, and a minimally productive cough. The most likely diagnosis is Legionnaires’ disease, secondary to the bacteria Legionella pneumophila.
Legionella pneumophila are rod-shaped bacteria that gram stain poorly, so ?

Answer 16

a silver stain must be used to visualize the rods (see arrows). Individuals at greatest risk for Legionnaires’ disease include the elderly, smokers, immunosuppressed people, and those with chronic obstructive pulmonary disease. Other findings suggestive of Legionnaires’ disease include altered mental status, hyponatremia, and fever >38.8°C. Transmission occurs by aerosolized water via building systems such as air conditioners.

Question 17

Giemsa stain is used for Chlamydia pneumoniae, which presents with fever and cough, but does not involve gastrointestinal symptoms. India ink stains for Cryptococcus neoformans, and Gomori methenamine silver stains for Pneumocystis jiroveci pneumonia, both of which are primarily seen in?

Answer 17

immunocompromised patients. Ziehl-Neelsen stain is used to diagnose Mycoplasma, which is more common in younger individuals.

Question 18

Legionnaires’ disease presents mainly in older patients, with fever, chills, minimally productive cough, shortness of breath, diarrhea, nausea/vomiting, hyponatremia, and altered mental status. Legionnaires’ disease is caused by the rod-shaped bacteria Legionella pneumophila, which can be diagnosed with?

Answer 18

silver stain.

Question 19

Based on the patient’s condition, nonadherence to medication, and results of cerebrospinal fluid (CSF) analysis, this patient most likely now has AIDS along with an opportunistic infection that affects the central nervous system (CNS). His cognitive impairment, progressive brain dysfunction, weakness, sensory deficits, and magnetic resonance imaging results point toward ?

Answer 19

progressive multifocal leukoencephalopathy (PML). PML occurs in severely immunocompromised individuals, such as those with HIV infection or AIDS, leukemia, or lymphoma.
PML is the result of the reactivation of latent JC virus, a polyomavirus carried by approximately 75% of all humans.

Question 20

In patients with HIV infection, this generally occurs at a CD4+ count of < 200/mm3. Because of the friend’s report, you should suspect that this patient is either noncompliant or has never initiated antiretroviral therapy, which explains the low CD4+ count. PML is a fatal CNS disease that causes demyelination of the white matter. Disease progression is subacute, and it is initially marked by visual field deficits, mental status changes, and weakness—all of which are seen in this patient. The disease progresses to blindness, dementia, coma, and death, typically within 6 months.

The gold standard for diagnosis of PML is ?

Answer 20

a brain biopsy. CSF analysis is usually unremarkable, but JC virus DNA can be detected by means of polymerase chain reaction in some individuals. The classic findings are seen in the magnetic resonance images, which reveal multiple, noncontrast-enhancing lesions in the white matter, primarily in the parietal and occipital lobes.

Question 21

Acute disseminated encephalomyelitis presents like multiple sclerosis, involving both sensory and motor deficits, and usually occurs after infections with no increased incidence in patients with HIV infection or AIDS.
Cryptococcal meningitis is an opportunistic disease, which may present with lumbar puncture findings of low glucose and high protein levels and the presence of cryptococcal antigen.
Guillain-Barré syndrome features?

Answer 21

ascending paralysis and a high albumin level, with a low white blood cell count on CSF findings. Sensory findings are highly unusual.
Herpes simplex meningitis typically affects the temporal lobes and would produce a lymphocyte-predominant CSF finding.

Question 22

In severely immunocompromised patients with subacute altered mental status, neurologic deficits, visual and motor changes, and ataxia, ?

Answer 22

progressive multifocal leukoencephalopathy should be considered as a diagnosis. It is caused by the reactivation of JC virus when the CD4+ count is < 200/mm3. Neuroimaging reveals multiple, nonenhancing white matter lesions with a normal cerebrospinal fluid profile.

Question 23

This patient has a history of unconsciousness plus fever, shortness of breath, and a productive cough with foul-smelling sputum. These findings are all consistent with aspiration pneumonia.
Individuals who have lost consciousness, who are debilitated, or who have a history of alcoholism are particularly susceptible to anaerobic lung infections because of an ineffective gag reflex and increased risk of aspirating bacteria from the oral cavity. Aspiration pneumonia produces sputum that is often described as “foul smelling.” The odor is likely caused by anaerobic bacteria from the oral cavity, and patients often have poor dentition. Common oral anaerobes include ?

Answer 23

Peptostreptococcus, Bacteroides fragilis, and Prevotella. Intravenous ampicillin plus sulbactam, in addition to metronidazole, are usually the first-line treatments for aspiration pneumonia.

Question 24

Klebsiella and Pseudomonas are less likely to be responsible for this patient’s infection, since he has an intact immune system. Streptococcus pneumoniae is the most common cause of community-acquired pneumonia, but this patient’s history of unconsciousness and a cough productive of foul-smelling sputum suggest that another organism is responsible for his infection. Obligate intracellular bacteria are typically associated with?

Answer 24

“atypical” pneumonia in which findings include a nonproductive cough.

Question 25

Anaerobic organisms commonly cause pneumonia in indviduals who may not have an intact gag reflex, such as those who have lost consciousness and those with a history of alcoholism or some form of debilitation. Peptostreptococcus is a common oral anerobe that can cause?

Answer 25

aspiration pneumonia. Common clinical features of aspiration pneumonia include a cough productive of foul-smelling sputum, which is associated with poor dentition.

Question 26

The patient is delivered to the ED in a desperate condition, with a high fever and racing heartbeat, appearing drowsy and confused. In light of his exposure history, progression of symptoms, and CSF analysis, this man was most likely infected with Naegleria fowleri, which manifests with a rapidly progressing meningoencephalitis that can progress to coma or death within 6 days.
The initial symptoms are indistinguishable from bacterial meningitis, including nausea, vomiting, seizures (this patient’s presenting symptom), and altered mental status. Infection typically occurs through swimming or diving in warm freshwater lakes or rivers. When water containing the ameba enters the body through the nose, the pathogen gains access to the CNS through ?

Answer 26

the cribriform plate. Microscopic analysis will reveal amoebas in the spinal fluid. Although amphotericin B has been effective in some cases of N. fowleri infection, the fatality rate for this rapidly progressing infection is over 97%.

Question 27

A skin abrasion can lead to many different viral and bacterial infections, though these infections would not demonstrate motile organisms on CSF wet mount.
Pseudomonas is a common pathogen causing malignant otitis externa, which can infect the external auditory canal.
Taenia solium, a tapeworm that can infect via the fecal-oral route, can cause ?

Answer 27

neurologic symptoms. This organism is endemic in Central and South America, sub-Saharan Africa, Eastern Europe, India, and Asia.
Respiratory viruses including rhinovirus and coronavirus are typically spread from person to person by contact with infected mucous membrane. Meningococcus and pneumococcus, which are common meningitis pathogens, are often spread through this route.

Question 28

Infection with Naegleria fowleri, an amoeba found in warm freshwater lakes and rivers, occurs when the pathogen gains access to the CNS via the?

Answer 28

cribriform plate. Infected individuals present with a rapidly progressing meningoencephalitis that can progress to coma or death within 6 days.

Question 29

A 35-year-old man who is a long-term intravenous drug abuser presents to the emergency department with a cough and fever. X-ray of the chest reveals faint bilateral interstitial infiltrates. Histologic analysis of induced sputum reveals trophozoite forms of Pneumocystis jirovecii.

Which of the following correctly states the function of the surface protein of the virus that predisposed this patient to his present infection?

Answer 29

The causal agent of AIDS is the HIV virus. The HIV surface protein gp120 binds to CD4 receptors on T helper lymphocytes. After a conformational shift, gp120 then binds to a chemokine coreceptor, either CCR5 on macrophages or CXCR4 on T cells. As a result HIV is engulfed into the cell.
Pneumonia caused by Pneumocystis jirovecii is an AIDS-defining illness, typically occurring when a patient’s CD4+ T-lymphocyte count decreases to <200/µL. Chest X-ray will typically show a bilateral, diffuse, reticular pattern with interstitial markings.

Question 30

The surface proteins of HIV are not directly involved in cellular killing. The gp120 viral surface protein plays a role in binding to host cell CD4. Another viral surface protein, gp41, is exposed after gp120 also binds to coreceptors CCR5 or CXCR4. gp41 aids fusion of the viral envelope to the host cell membrane.

The surface proteins of HIV bind to CD4 receptors, not CD3 receptors. However, it is true that CD3 receptors are found on both helper T lymphocytes and cytotoxic T lymphocytes.

The surface proteins of HIV bind to CD4 receptors, not CD8 receptors. CD4 receptors are found on helper T cells, whereas CD8 receptors are found on cytotoxic T cells. HIV selectively targets CD4+ helper T cells by binding to the CD4 receptor.

The function of the surface proteins of HIV is to allow entry into the helper T cells. Although the T helper cell will ultimately die from infection, its death is not due to ?

Answer 30

the surface proteins but rather to the uncontrolled replication of the virus.

Pneumocystis jirovecii pneumonia is an AIDS-defining illness that occurs when CD4+ counts drop below 200/µL. The HIV surface proteins gp120 and gp41 cause binding and fusion, respectively, to allow entry into CD4+ helper T cells.