Micro USMLE 8-29(20) (qmax 8/29 incorrect qs

Question 1

The patient is brought to the ED by her mother after exhibiting strange behavior and suffering amnesia. Based on her clinical presentation, lumbar puncture, and MRI, this patient most likely has?

Answer 1

encephalitis due to herpes simplex virus (HSV) type 1. The symptoms of HSV-1 encephalitis can range from amnesia and behavioral changes (eg, hypomania) to Klüver-Bucy syndrome (characterized by inappropriate sexual behaviors and mouthing of objects). Later stages of the disease can include coma and death.

Question 2

On the lumbar puncture, viral meningitis should produce?

Answer 2

Increased lymphocytes
Normal to increased protein
Normal to decreased glucose

Elevated numbers of RBCs might also be noted, due to hemorrhage from the necrosis of brain tissue. CT or MRI of the brain typically demonstrates focal pathology in the temporal lobe

Question 3

HSV-1 is the most common cause of sporadic encephalitis. HSV-2 is more likely to cause a meningitis, which is distinguished from encephalitis by the absence of significant cognitive changes. Other diseases caused by HSV-1 include?

Answer 3

gingivostomatitis (with lesions around the lips and gums), keratoconjunctivitis, and herpes labialis. HSV-2 is associated with herpes genitalis and neonatal herpes.

Question 4

Coxsackievirus is a common cause of viral meningitis and dilated cardiomyopathy, but it doesn’t demonstrate the same effects on the temporal lobe.
Streptococcus pneumoniae is the most common cause of otitis media, as well as meningitis overall, but this immunized patient’s lumbar puncture do not reflect a bacterial cause (high protein, low glucose, and neutrophil prominence).
The lumbar puncture and immunization status also helps to rule out an infection with?

Answer 4

Haemophilus influenzae, which can cause epiglottitis in children.
Toxoplasma gondii is a parasite that can lead to chorioretinitis, especially in the gestational period. However, neuroimaging would be expected to show distinctive ring-enhancing lesions.

Question 5

Herpes simplex encephalitis due to HSV-1 can affect any age group but is most often seen in persons under age 20 or over age 40. Symptoms can include headache and fever for up to 5 days, followed by personality and behavioral changes, seizures, hallucinations, and altered levels of consciousness. Lumbar puncture results are often consistent with?

Answer 5

viral meningitis, although MRI may be normal early in the course of illness. Temporal lobe involvement and early involvement of white matter are typical.

Question 6

This patient presents with fever and fatigue, shortly after a suspected tick bite acquired on a camping trip in an endemic area. A tender skin lesion at the site of the bite is well demarcated and has a black base, a finding that suggests?

Answer 6

ulceroglandular tularemia, one of the diseases caused by the facultative intracellular gram-negative rod-shaped Francisella tularensis.

Question 7

The most common means of transmission of ulceroglandular tularemia (80% of cases) is via contaminated rabbit blood. This bacterium can be transmitted to humans by ?

Answer 7

a tick or deerfly bite or through direct contact with an infected animal. Cases of tularemia have been described throughout the continental United States, with a predominance in the Midwest and Southeast. It’s important to note that the form of F tularensis may vary; it can be described as a either a coccobacillus or a rod.

Question 8

Although Lyme disease, caused by Borrelia burgdorferi, and Rocky Spotted Mountain fever, caused by Rickettsia rickettsi, are transmitted by ticks, they do not cause?

Answer 8

the formation of an ulcer with a black base. Brucella melitensis and Nocardia asteroides are not transmitted by the bite of a tick or flea and are not associated with an ulcer with a black base. Although Yersinia pestis can cause an ulcerative lesion with a black base, the geographic area in which the infection was transmitted and the patient’s description of a tick vector, rather than a flea, make this organism less likely to be the cause of his symptoms.

Question 9

Francisella tularensis is carried by rabbits and other small mammals and can be transmitted to humans via tick or deerfly bites or through direct contact with an infected animal. Infection may lead to ulceroglandular tularemia, characterized by a well-demarcated skin lesion with?

Answer 9

a black base, along with systemic symptoms.

Rabbit Tick Bites Contact Animals Black Base Ulceroglandular tularemia

Question 10

This patient presents with the classic Charcot triad of right upper quadrant pain, jaundice, and fever, typically found in patients with cholangitis. The patient’s history also reveals the possibility of long-standing gallstones, since eating fatty food elicits pain. Migration of these stones into the cystic duct and then the common bile duct leads to the potential for infection?

Answer 10

Bacterial cholangitis is defined as a bacterial infection of the bile ducts.

Cholangitis can result from any condition obstructing bile flow, most commonly choledocholithiasis. The bacteria are usually enteric gram-negative rods, such as Escherichia coli or Klebsiella, Bacteroides, or Enterobacter species, which enter the bile duct via the ampulla of Vater. Leukocytosis with neutrophilia and an elevated band cell count are commonly present as well.

Question 11

Acute pancreatitis usually presents with epigastric pain radiating to the back and increased serum lipase levels. Patients with acute viral hepatitis may also have symptoms of jaundice and fever, but not neutrophilia and a history suggestive of?

Answer 11

cholelithiasis. Findings in patients with cholecystitis may include right upper quadrant pain and nausea, but marked fever and leukocytosis are less common. Primary biliary cholangitis is an autoimmune reaction that usually presents with pruritus or as abnormal liver enzyme levels in an individual without symptoms.

Question 12

This patient arrives with his sister complaining of new-onset seizures and decreased visual acuity, which is confirmed in his physical exam by a right homonymous hemianopia. These findings, along with his low CD4 count and enlarged lymph nodes, indicate that he may have toxoplasmosis, which results from a?

Answer 12

Toxoplasma gondii infection. Toxoplasmosis occurs in patients with HIV whose CD4 count is <100 cells/μL. It most commonly manifests with encephalitis characterized by seizures and/or focal neurologic deficits. The classic picture on a CT scan or an MRI of the head is a ring-enhancing lesion with surrounding edema and mass effect (as shown in this MRI). The specific visual field defect in this patient is due to the cerebral lesions causing a focal neurologic deficit.

New-onset seizures in an HIV-positive patient with a CD4 count <100 cells/µL is highly suggestive of toxoplasmosis. Other manifestations are chorioretinitis, which is characterized by eye pain and decreased visual acuity, as seen in this patient.

Question 13

Another pathogen that causes similar symptoms is cytomegalovirus (CMV). CMV causes retinitis, rather than specific cuts of visual fields, and does not often cause new-onset seizures.
Aspergillus fumigatus typically causes pneumonia but not ocular or neurologic symptoms.
Candida albicans infection manifests with?

Answer 13

esophageal and oropharyngeal symptoms in immunocompromised patients, with disseminated disease rare except in severe AIDS.
Neurocysticercosis infection can manifest similarly with new-onset seizures, but occurs more commonly outside of the United States, especially in people who have recently eaten raw or undercooked pork.

Question 14

Toxoplasmosis is a central nervous system infection of HIV patients (with CD4 <100 cells/μL) that leads to focal neurologic deficits and chorioretinitis. Toxoplasmosis has been reported as the most common opportunistic infection in HIV/AIDS in developed countries and is the most common cause of?

Answer 14

focal brain lesions, coma, and death. It commonly causes encephalitis in HIV-infected patients.

Question 15

This patient presents with the classic symptoms (fever, sore throat, anterior cervical lymphadenopathy, lack of cough) of streptococcal pharyngitis (strep throat). This is caused by ?

Answer 15

the catalase-negative, ß-hemolytic, bacitracin-sensitive Streptococcus pyogenes.

Catalase is an enzyme that catalyzes the breakdown of hydrogen peroxide into water. ß-Hemolysis occurs when there is complete lysis of RBCs in the media surrounding the bacterial colony (see image); this lysis is caused by the streptolysin exotoxin. Bacitracin is an antibiotic that is commonly used to characterize bacterial strains. Diagnosis is confirmed with a rapid strep test or with throat swab culture, and treatment is with penicillin.

Question 16

Catalase-negative, a-hemolytic, optochin-resistant describes Streptococcus viridans, which does not present with oropharyngeal exudates. Streptococcus pneumoniae is catalase negative, a-hemolytic, and optochin sensitive and, like S. viridans, does not cause oropharyngeal exudates. Streptococcus agalactiae is ?

Answer 16

catalase negative, ß-hemolytic, and bacitracin resistant but is unlikely to be the cause of this patient’s infection because it typically affects neonates. Catalase-positive, coagulase-negative, novobiocin-sensitive describes Staphylococcus epidermidis, which does not typically infect the upper respiratory tract.

Question 17

This patient has a painful penile ulcer and inguinal lymphadenopathy with purulent discharge, a classic presentation of chancroid. Chancroid is a sexually transmitted disease caused by Haemophilus ducreyi, which is a?

Answer 17

gram-negative coccobacillus. The genital lesions may begin as small papules that rapidly evolve into painful ulcers with erythematous bases that bleed easily with mechanical manipulation. Painful, swollen inguinal lymph nodes, often unilateral, develop in about 30% of infected persons. In 50% of these patients, the swollen lymph nodes will rupture and drain pus. An example of chancroid infection is displayed in the image below. Treatment options for chancroid include azithromycin, ceftriaxone, and ciprofloxacin.

Question 18

The other descriptions apply to other sexually transmitted pathogens with different presentations. Neisseria gonorrhoeae is a gram-negative diplococcus that presents with urethritis, cervicitis, and pelvic inflammatory disease, but not genital ulcers. Herpes simplex virus is a double-stranded linear DNA virus that presents with genital lesions best described as small vesicles on erythematous bases that rupture into open shallow ulcers. Treponema pallidum (syphilis) is a?

Answer 18

gram-negative spirochete that presents with a painless chancre. Chlamydia trachomatis is an obligate intracellular bacterium that may produce purulent lymph nodes in patients with lymphogranuloma venereum, but the initial lesions are painless papules or ulcers.

Question 19

Genital ulcers are associated with chancroid, syphilis, lymphogranuloma venereum, and herpes simplex infection. Chancroid is caused by H. ducreyi, ?

Answer 19

a gram-negative coccobacillus. A chancroid ulcer is painful with an erythematous base that bleeds with mechanical manipulation; purulent inguinal lymph nodes are also associated with this infection.

Question 20

The boy is brought in to see his physician after multiple vomiting episodes and a fever. His symptoms—including fever, tender neck, and maculopapular rash with petechiae on his trunk—and laboratory findings are consistent with meningitis and septicemia caused by ?

Answer 20

Neisseria meningitidis. This gram-negative diplococcus is the second most common cause of meningitis in children aged 6 months to 6 years and is the leading cause of meningitis in older adolescents and young adults. The bacterium grows best on Thayer-Martin VCN medium, which contains antibiotics that kill competing bacteria and fungi. However, if it is obtained from sterile sources such as cerebral spinal fluid (CSF), it can be isolated on nonselective media.

Question 21

The CSF sample would most likely show a white blood cell count > 1000/mm3 with mostly neutrophils, glucose < 40 mg/dL, and protein 100–500 mg/dL, in keeping with the bacterial origin. Once in the bloodstream, the bacteria can cause a characteristic petechial rash (like that shown in the image) caused by endotoxin, which predisposes an individual to?

Answer 21

Waterhouse-Friderichsen syndrome (sepsis with adrenal insufficiency and potential adrenal hemorrhage). Adrenal insufficiency presents with anorexia, nausea, vomiting, abdominal pain, weakness, fatigue, fever, and confusion; it can even cause coma.

Question 22

Ascending peripheral nerve paralysis would be associated with Guillain-Barré syndrome, which may occur after infection with Campylobacter jejuni.
Myocardial infarction would be associated with Kawasaki disease, a medium-sized arterial vasculitis, which can occur in children.
Sudden onset of fever, lethargy, and a new heart murmur would be associated with?

Answer 22

acute bacterial endocarditis.
Right-sided upper and lower facial droop would be associated with Bell palsy, a possible sequela of herpes simplex virus activation or Lyme disease.

Question 23

Neisseria meningitidis is a gram-negative diplococcus that is a common cause of bacterial meningitis. It is often associated with a petechial rash in children and young adults. In severe cases, it can cause Waterhouse-Friderichsen syndrome, a condition characterized by?

Answer 23

sepsis and adrenal insufficiency due to adrenal hemorrhage.

Question 24

This young patient who is likely unvaccinated (never seen a doctor) and presents with 1 week of catarrhal symptoms (malaise, runny nose, cough) along with post-tussive vomiting most likely has pertussis, or “whooping cough.” Pertussis is caused by the gram-negative coccobacillus Bordetella pertussis. The characteristic presentation of pertussis allows for diagnosis to be made clinically. Nevertheless, culture of the nasopharynx can be useful when the diagnosis is uncertain. Difficulties culturing B. pertussis led to?

Answer 24

The development of Bordet-Gengou agar, which is made with blood, potato extract, glycerol, and antibiotics. Regan-Lowe agar, a charcoal blood agar, may also be used to culture B. pertussis.

Question 25

Pertussis was predominantly a childhood disease before the widespread use of immunizations, and now mostly occurs in unvaccinated children and older patients with waning immunity. It begins with upper respiratory symptoms (eg, malaise, rhinorrhea, congestion) and may progress to episodes of intense coughing that begin with a “whooping” inhale and result in vomiting. Lung auscultation and chest radiography are usually normal. Lymphocytosis induced by pertussis toxin is common and can cause fever. Treatment involves antibiotic therapy with a ?

Answer 25

macrolide, such as azithromycin, as well as prophylaxis for all close contacts regardless of vaccination status.

Question 26

MacConkey agar contains bile salts that inhibit the growth of gram-positive organisms. MacConkey agar is optimized for the culture of lactose-fermenting enteric bacteria.
Thayer-Martin agar, also known as Thayer-Martin VCN medium, is a blood agar supplemented with antimicrobials (VCN = vancomycin, colistin [polymyxin], and nystatin). It restricts the growth of?

Answer 26

gram-positive organisms and gram-negative organisms other than Neisseria spp, making it ideal for the culturing of N. gonorrhea and N. meningitidis.

Question 27

Haemophilus influenzae is a fastidious organism and requires ?

Answer 27

both factors V and X to grow; it can be grown on blood agar alongside Staphylococcus aureus, which facilitates release of additional factor X.

Question 28

Löffler’s agar contains horse serum, meat infusion, and dextrose and selectively grows?

Answer 28

the genus Corynebacterium.

Question 29

Bordetella pertussis causes pertussis (“whooping cough”). When diagnosis is uncertain, it can be cultured from the nasopharynx onto ?

Answer 29

Bordet-Gengou agar or Regan-Lowe agar.

Question 30

This girl’s symptoms began 4 days ago with a fever, headache, nausea, and a rash on her cheeks. She now presents to the emergency department complaining of a rash on her trunk and legs. Her temperature and white blood cell count are both elevated. These findings are highly suggestive of ? Parvovirus also causes aplastic anemia in patients with sickle cell anemia and hereditary spherocytosis.

Answer 30

fifth disease.
Parvovirus B19 is a single-stranded negative DNA virus that is the causative organism of fifth disease (also called erythema infectiosum), which typically affects children 5–10 years old. This condition is characterized by an initial prodromal phase that includes findings such as a low-grade fever, headache, and gastrointestinal symptoms. The virus causes an erythematous rash that looks like both cheeks have just been slapped (like shown in this image). In addition, a pruritic maculopapular rash starts on the arms and spreads to the trunk and legs.

Question 31

Single-stranded positive RNA viruses (such as coxsackie virus), single-stranded enveloped negative RNA viruses (such as paramyxovirus), and single-stranded enveloped positive RNA viruses (such as the rubella virus) do not present with a slapped cheek rash as presented in this patient’s symptoms. Catalase-negative, coagulase-negative diplococci describe ?

Answer 31

streptococcus bacteria species which produce diseases such as pharyngitis, cellulitis, and scarlet fever.

Parvovirus B19 is the causative organism of fifth disease (erythema infectiosum), which is characterized by an erythematous rash on both cheeks.