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Select the ONE answer that is BEST in each case.
A 43-year-old man developed a cough shortly after returning from a 1-month hiking trip in California. While there, he was hiking in the central California valleys. During his trip, he had developed a “flu-like” illness consisting of fever, cough, and muscle pains, which resolved spontaneously. A CXR shows a thin-walled cavity in the right upper lobe, and the sputum reveals fungal elements. Which of the following is the most likely causative organism?
Coccidioidomycosis is the usual cause of pulmonary cavitation resulting from fungal infection. A rarefaction may be demonstrable in a pneumonic lesion within 10 days of onset. In the United States, most cases are acquired in California, Arizona, and western Texas.
An 8-year-old boy from an impoverished innercity area has never been vaccinated appropriately. He develops fever, cough, and coryza. The next day, blue white spots develop on the buccal mucosa. On the third day, an erythematous, nonpruritic maculopapular rash develops on the face and spreads over the entire body. Which of the following is the most likely complication?
The most common complication of measles is otitis media, other complications include mastoiditis, pneumonia, bronchitis, encephalitis, and lymphadenitis. Otitis media is usually a bacterial superinfection, and should be treated with antibiotics.
A 6-year-old boy develops symptoms of cough, fever, and malaise followed by a generalized maculopapular rash that has spread from the head downwards. A clinical diagnosis of measles is made. A few days after the onset of the rash he is drowsy, lethargic, and complaining of headache. A lumbar puncture, electroencephalogram (EEG), and computerized tomography (CT) of the brain exclude other etiologies and confirm the diagnosis of encephalitis. Which of the following is the most likely delayed neurologic complication of measles virus encephalitis?
Subacute sclerosing panencephalitis causes involuntary spasmodic movements and progressive mental deterioration, frequently ending in death within a year. It usually occurs in children whose measles occurred at an early age (= 2 years). It occurs 6–8 years after the primary infection. It presents with nonspecific symptoms such as poor school performance or mood and personality changes. It then progresses to intellectual decline, seizures, myoclonus, ataxia, and visual disturbances. Continued deterioration results in inevitable death.
A 27-year-old man presents with diarrhea. He returned 3 weeks ago from a trip to rural South America. Over the past few days, he has gradually developed lower abdominal pain and diarrhea. Now the symptoms are much worse with eight stools a day consisting mostly of mucus and blood. He is afebrile, the abdomen is tender in left lower quadrant, and the remaining examination is normal. His stool is mostly comprised of blood and mucus. Which of the following is the most appropriate initial diagnostic test?
Demonstration of hematophagous trophozoites of E. histolytica in stool confirms the diagnosis. The trophozoites are rapidly killed by drying, so wet mounts of stool should be examined.
A 4-year-old boy is sent to the emergency room because of clinical suspicion of meningitis. He has been ill for 2 days with fever and lethargy. On examination, he is febrile, the neck is stiff, and papilledema is present. There is no rash, the lungs are clear, and heart sounds normal. Which of the following is the most likely causative organism?
Since the introduction of H. influenzae type B vaccine, S. pneumoniae has become the most common type of meningitis in infants and toddlers.
Which of the following is a contraindication to receiving the live rubella vaccine?
Pregnancy or anticipated pregnancy within 4 weeks of vaccination is a contraindication to receiving the rubella vaccine. There is a theoretical concern that fetus might develop congenital rubella syndrome from the live attenuated virus used for the vaccine. Vaccination is usually given to children combined with measles and mumps vaccine between 12 and 15 months of age, and then repeated during childhood at age 4–6 years. It is given even to children with HIV infection. Infants <1 year old can be given the vaccine but may not develop adequate immunity and should still be given the recommended two doses.
A 24-year-old woman presents with chills and rigors. She looks unwell, and her temperature is 39.4C, blood pressure 100/60 mm Hg, pulse 110/min, and oxygen saturation 95%. There is a 3/6 pansystolic murmur at the right sternal border, which increases with inspiration. Her arms have multiple tattoos and needle marks from injection drug use. Blood cultures (2/2 sets) are positive for S. aureus, and she is started on appropriate antibiotics. Her renal function is mildly impaired and her urinalysis is positive for protein, and microscopy reveals red cell casts. Which of the following mechanisms is the most likely explanation for her renal abnormalities?
The clinical manifestations of infective endocarditis are a result of three factors: (1) direct infection in the heart, (2) septic emboli, and (3) high levels of circulating immune complexes. Glomerulonephritis, arthritis, and many of the mucocutaneous lesions are secondary to circulating immune complexes. Renal emboli cause hematuria and flank pain, but rarely impair renal function.
A 22-year-old university student complains of fatigue and malaise for the past 2 weeks. She also reports feeling feverish, and recently had a sore throat. Physical examination reveals enlarged tonsils and palpable cervical lymph nodes. There is also tenderness in the right upper quadrant on deep palpation, and minimal splenomegaly. Laboratory data show hemoglobin 13 g/dL; hematocrit 40%; platelets 340,000/mL; WBC 9400/mL, with 35% segmented neutrophils, 1% eosinophils, and 64% lymphocytes, of which 36% were atypical. A heterophil antibody (sheep cell agglutination) test is positive. Which of the following is the most appropriate initial treatment for this condition?
Adequate rest is the treatment of choice, but forced bed rest is not necessary. Glucocorticoids hasten defervescence and resolution of pharyngitis but are not routinely used. Acyclovir halts oropharyngeal shedding of EBV but has minimal effect on the clinical disease. Similarly alpha-interferon and ganciclovir have antiviral efficacy but have no role to play in uncomplicated infectious mononucleosis. Antibiotics are not helpful, and ampicillin is likely to cause a pruritic maculopapular rash in most patients.
A 23-year-old woman presents with a painless chronic vulvar ulcer. She recently arrived to study in the United States from Southern India. The lesion began as a papule and then ulcerated. It has persisted for several months. Currently, physical examination reveals a painless elevated area of beefy red, friable granulation tissue. She has been sexually active for several years. Which of the following is the most likely causative organism?
Donovanosis, or granuloma inguinale, is a mildly contagious, chronic, indolent disease that can be sexually transmitted. Calymmatobacterium granulomatis, a Gramnegative intracellular bacterium, is felt to be the cause. It is endemic in many tropical areas. Daily doxycycline or weekly azithromycin until the lesions are healed are the usual treatments. Erythromycin is used in pregnant patients.
A 20-year-old woman presents with headache, fever, and neck stiffness. On examination, her blood pressure is 100/70 mm Hg, pulse 100/min, temperature 38.6C, and the neck is stiff and painful to flex and extend. The ears, throat, and sinuses are normal, there are no focal neurologic signs, and the remaining examination is normal. There are no reported similar cases in the community. Which of the following is the most likely source of her infection?
S. pneumoniae colonizes the nasopharynx of 5–10% of healthy adults and up to 20–40% of children. The source of pneumococcal meningitis is either direct extension from middle ear or sinus infections, or via seeding from a bacteremia. In the latter circumstance, bacteremia from pneumonia would be more likely than from infective endocarditis.
A 44-year-old renal transplant patient develops severe cough and shortness of breath on exertion. On examination, he appears dyspneic, respirations 24/min, pulse 110/min, and oxygen saturation 88%. His lungs are clear on auscultation and heart sounds are normal. CXR shows bilateral diffuse perihilar infiltrates. Bronchoscopy and bronchial brushings show clusters of cysts that stain with methenamine silver. Which of the following is the most appropriate next step in management?
The patient is infected with Pneumocystis organisms invading an immunocompromised host. The treatment of choice is trimethoprimsulfamethoxazole. Alternate therapies include pentamidine (highly toxic) and trimetrexate plus folinic acid.
A34-year-old man presents with diarrhea 3 weeks after returning from a trip to rural South America. Over the past few days, he has gradually developed lower abdominal pain and diarrhea. Now the symptoms are much worse with eight stools a day consisting mostly of mucus and blood. He is afebrile, the abdomen is tender in left lower quadrant, and the remaining examination is normal. His stool is mostly comprised of blood and mucus, and stools tests show trophozoites of Entamoeba histolytica. Which of the following is the most likely site of extraintestinal involvement?
All the sites mentioned can be involved by amebiasis, but the liver is the most common. Most travelers who develop an amebic liver abscess will do so within a few months of their return. Pleuropulmonary and pericardial involvement results from extension from the liver.
A 20-year-old woman complains of headache and discomfort in both sides of her jaw. Physical examination reveals enlarged parotid glands that are slightly tender on palpation. There is reddening of the orifice of Stensen’s duct on intra oral examination; her temperature is 38.3°C, and the pulse rate is 80/min. Laboratory data show hemoglobin 14 g/dL; hematocrit 40%; WBC 11000/mL, with 33% segmented neutrophils, 7% monocytes, and 60% lymphocytes. Which of the following diagnostic tests will help to confirm the diagnosis of epidemic parotitis?
Acute and convalescent titres of specific IgG antibodies will confirm the diagnosis of mumps. A single test revealing a specific IgM antibody can also confirm the disease. Urine, saliva, and throat swabs will grow the mumps virus, but blood does not. Salivary amylase is elevated but is relatively nonspecific. Of course, a typical presentation during an epidemic probably does not require any confirmatory tests. Sporadic cases require more active confirmation. Other causes of parotitis requiring specific treatment include calculi, bacterial infections, and drugs. Tumors, sarcoid, TB, leukemia, Hodgkin’s disease, Sjögren’s syndrome, and lupus erythematosus can also cause parotid enlargement.
Three hours after a church social, eight people develop severe diarrhea. Other symptoms included nausea, vomiting, and abdominal cramps. Food served included chicken salad and cream-filled pastries. All affected individuals had the chicken salad. Which of the following is the most likely causative organism?
Staphylococcal enterotoxin food poisoning is characterized by violent GI upset with severe nausea, cramps, vomiting, and diarrhea. It occurs very rapidly after ingestion (1–6 hours) and usually resolves by 12 hours.
A young woman complains of hair loss, loss of hair luster, and intense scalp irritation. Examination reveals patches of hair loss with tiny little black dots where the hair shaft has broken off. A Wood’s light examination is positive. Which of the following is the most likely diagnosis?
The patient has tinea capitis, which may be caused by Trichophyton or Microsporum species. It may be successfully treated with topical azole drugs (e.g., clotrimazole). More severe infections are usually treated with systemic medications.
A 9-year-old boy has a severe sore throat with fever and dysphagia. On examination, there are grayish-white papulovesicular lesions on an erythematous base that ulcerate. They are located on the soft palate, anterior pillars of the tonsils and uvula. There are no lesions on the gingiva, tongue, or lips. A clinical diagnosis of herpangina is made. Which of the following is the most likely causative organism?
Coxsackie A viruses may cause a number of syndromes, including herpangina, exanthem, aseptic meningitis, common cold, paralysis, pneumonitis, and summer febrile illness. It is distinguished from HSV-1 herpes stomatitis by the fact that most of the lesions are concentrated in the posterior portion of the mouth and that there is no gingivitis. The other virus does not cause oral lesions. HSV-2 can occasionally cause oral lesions.
A young man has recently been bitten by a stray dog. He has a penetrating wound to the right forearm. The dog is nowhere to be found. In the emergency room, the wound is cleaned with water and povidone-iodine solution. Which of the following is the most appropriate next step in management?
Rabies is transmitted through the saliva of infected animals. Once clinical signs develop, the disease is almost 100% fatal. Symptoms of rabies may include apathy as well as hyperexcitability. Finding Negri bodies in nerve cells of the brain in infected animals confirms the diagnosis. Polymerase chain reaction for detection of viral material is another method of confirming the diagnosis. In cats and dogs that are not available for observation (lasting 10 days) to determine if they have signs of rabies, public health authorities should be consulted to determine the potential risk of rabies in the animal based on local rates of rabies in wild animals. Alternatively if there is a high risk the animal is infected, then postexposure prophylaxis should be started with rabies vaccination on days 0, 3, 7, 14, and 28 as well as one dose of rabies immune globulin on day 0.
Which of the following malignancies in the United States is most likely to contain EBV deoxyribonucleic acid (DNA) in a non-HIV patient?
EBV genetic material has been found in association with many malignancies. In Africa, about 90% of patients with Burkitt’s lymphoma have an association with EBV, but in the United States, only 15% of cases are associated with EBV. In contrast, almost all cases of anaplastic nasopharyngeal carcinoma and also HIVrelated CNS lymphomas are associated with EBV genetic material.
A 24-year-old man complains of fatigue, malaise, fever, and a sore throat. He was previously well, but now feels tired all the time and has to rest multiple times a day. Physical examination shows enlarged tonsils and palpable anterior and posterior cervical, axillary, and inguinal lymph nodes. There is also tenderness in the right upper quadrant with a liver span of 10 cm. Laboratory data is significant for a heterophil antibody (sheep cell agglutination) test that is positive. Which of the following rare complications can be associated with this condition?
Splenic rupture occurs during the second or third week of the illness and can be insidious or abrupt in presentation. Surgery is required. Hemorrhage is not a usual complication of infectious mononucleosis. Over 90% of cases are benign and uncomplicated, but liver involvement is clinical in 5–10%. Over 85% of EBV-associated neurologic problems resolve spontaneously. Although hemorrhage does not occur, autoimmune hemolytic anemia can occur. It is usually mediated by IgM antibodies with anti-i specificity.
A 40-year-old man develops erythema nodosum, conjunctivitis, and a pleural effusion. Over several weeks, pulmonary lesions lead to cavitation and a large, thin-walled cavity. He was traveling in Arizona before becoming ill. Sputum samples reveal mature spherules. Which of the following is the most likely diagnosis?
Coccidioidomycosis may present with a syndrome of erythema nodosum, fever, and conjunctivitis. Serious complications include cavitating lung lesions or meningitis.
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