Inmunología

Question 1

A 26-year-old woman comes to the physician because of several days of fever, abdominal cramps, and diarrhea. She drank water from a stream 1 week ago while she was hiking in the woods. Abdominal examination shows increased bowel sounds. Stool analysis for ova and parasites shows flagellated multinucleated trophozoites (Giardia). Further evaluation shows the presence of antibodies (IgA) directed against the pathogen. Secretion of these antibodies most likely requires binding of which of the following?

Answer 1

The binding of the CD40 membrane receptor on B cells with CD40 ligand (CD40L) on the surface of T helper cells is the second step in immunoglobulin class switching and is necessary for the secretion of IgA in patients with Giardia lamblia infection. The first step in B cell activation is the binding of antigen-presenting MHC II on B cells to the CD4 receptor on T helper cells.

Question 2

What is the triad of hemolytic uremic syndrome (HUS) and which toxin is the most common cause in pediatric HUS?

Answer 2

This child presents with the triad of thrombocytopenia, signs of hemolysis (anemia, ↑ LDH, schistocytes), and renal dysfunction
The Shiga-toxin-producing E. coli (STEC) is the most common cause of pediatric HUS.

Question 3

A 44-year-old man with HIV comes to the physician for a routine follow-up examination. He has been nonadherent with his antiretroviral medication regimen for several years. He appears chronically ill and fatigued. CD4+ T-lymphocyte count is 405/mm3. Further evaluation of this patient is most likely to show which of the following findings?

Answer 3

Violaceous skin lesions in a patient with HIV describe Kaposi sarcoma. HIV patients are at a higher risk of Kaposi sarcoma at variable CD4 counts, even above 400/mm3.

Question 4

An investigator is conducting an experiment to develop a new drug against HIV infection. HIV-infected and uninfected CD4 T-cell lines are mixed in-vitro with a chemically modified synthetic peptide triazole complex. The complex is found to have a high binding affinity to the gp120 protein, irreversibly inhibiting its function and reducing CD4 T cell infection. Inhibition of which of the following steps of HIV infection is the most likely therapeutic effect of this experimental drug?

Answer 4

Attachment to host CD4 T-cells

Question 5

Fusion and entry of HIV into host CD4 T cells are mediated by the HIV envelope glycoprotein ___

Answer 5

41

Question 6

A 4-month-old boy is brought to the physician because of a painful lesion on his right leg. Yesterday, he received all of his scheduled childhood immunizations, including the second dose of the diphtheria, tetanus, and acellular pertussis vaccine, which was administered in the right quadriceps. Physical examination shows a 2-cm ulcer with surrounding induration over the right anterolateral thigh. A skin biopsy of the lesion shows localized edema, skin necrosis, neutrophilic infiltration, and complement deposition. Which of the following is the most likely cause of his symptoms?

Answer 6

Arthus reaction

A rare, localized, type III hypersensitivity reaction characterized by immune complex deposition in the walls of dermal blood vessels.

Question 7

A 60-year-old man comes to the office because of an 8-month history of cough, night sweats, shortness of breath, and fatigue. He has also had a 9-kg (19.8-lb) weight loss during this time. He appears pale. Abdominal examination shows hepatosplenomegaly. His leukocyte count is 80,000/mm3 and his leukocyte alkaline phosphatase level is increased. A peripheral blood smear shows > 82% neutrophils with band forms and immature and mature neutrophil precursors. An x-ray of the chest shows a 9-mm right hilar nodule. Which of the following is the most likely cause of this patient’s laboratory findings

Answer 7

A leukemoid reaction is characterized by profound leukocytosis with a proportionate increase in all elements of the myeloid lineage (neutrophils, immature and mature precursors) and elevated leukocyte alkaline phosphatase (LAP), as seen in this patient.

Question 8

This patient presents with recurring respiratory infections, lymphadenopathy, and inflammatory, pustular lesions, starting at a very young age. Together, these features suggest impaired functioning of phagocytic cells, making him especially susceptible to infection with catalase-positive organisms (e.g., S. aureus, E. coli, Aspergillus).

Answer 8

Defective NADPH oxidase

The NADPH oxidase enzyme is responsible for the respiratory burst (oxidative burst) within phagolysosomes, a component of phagocytic cells, which causes a rapid release of reactive oxygen species (ROS) that can destroy bacteria. In patients with defective NADPH oxidase, also known as chronic granulomatous disease (CGD), this reaction does not occur.

Question 9

This patient’s symptoms, together with his recent travel history, the findings of the physical examination, and serum studies (especially anti-HAV antibodies) suggest acute infection with hepatitis A virus (HAV). Virus-infected cells produce Interferon α and Interferon β, which upregulate MHC I expression to facilitate the recognition and destruction of infected cells. They also downregulate protein synthesis to prevent viral replication. This process also results in…

Answer 9

Increased breakdown of intracellular RNA

Besides promoting the expression of MHC class I proteins on the surface of virus-infected cells, interferon α and interferon β induce the activation of various enzymes that promote the antiviral state of the cell, including ribonuclease L. Ribonuclease L is an enzyme that mediates the degradation of cellular and viral RNA and thereby inhibits viral protein synthesis.

Question 9

A 22-year-old man comes to the physician because of abdominal pain, diarrhea, and weight loss that started after a recent backpacking trip in Southeast Asia. He does not smoke or drink alcohol. His leukocyte count is 7,500/mm3 (61% segmented neutrophils, 13% eosinophils, and 26% lymphocytes). Stool microscopy shows rhabditiform larvae (Strongyloides stercoralis). This patient is most likely to develop which of the following?

Answer 9

Perianal serpiginous rash

Strongyloides stercoralis is a nematode endemic to Southeast Asia that is transmitted via larval penetration of intact skin (usually when bare feet come into contact with contaminated soil).

Question 9

This patient presents with the thumbprint sign (thickening of the epiglottis) on x-ray of the neck as well as classic clinical features (dysphagia, drooling, distress) of acute epiglottitis due to Haemophilus influenzae infection.
The drug of choice for H. influenzae prophylaxis is rifampin, what is its mode of action?

Answer 9

Inhibition of DNA-dependent RNA-polymerase

Inhibition of prokaryotic DNA-dependent RNA polymerase is the mechanism of rifampin, the drug of choice for prophylaxis for Haemophilus influenzae.

Question 10

A 2-month-old boy is brought to the pediatrician for a routine check-up. His mother says he is feeding well and has no concerns. He is at the 85th percentile for height and 82nd percentile for weight. Immunizations are up-to-date. Results of serum hepatitis B surface IgG antibody testing are positive. Which of the following best explains this patient’s hepatitis B virus status

Answer 10

Passive Immunity

IgG is the most common type of antibody and can indicate prior infection or immunization.

Question 11

Recurrent infections (bacterial and fungal), failure to thrive, absent tonsils, and absent thymus shadow on x-ray suggest severe combined immunodeficiency (SCID). It also shows

Answer 11

Decreased circulating T cells

This patient’s severe combined immunodeficiency (SCID) is most likely due to an autosomal recessive adenosine deaminase deficiency (the second most common cause of SCID), which results in disrupted purine metabolism and accumulation of metabolites (including deoxyadenosine and dATP) that are toxic to maturing lymphocytes.

Question 12

Arthritis, fatigue, discoid rash, and oral ulcers are suggestive of systemic lupus erythematosus (SLE). This patient’s history of unprovoked deep vein thromboses (DVTs) should raise concern for antiphospholipid syndrome (APS). They also present

Answer 12

Rapid plasma reagin test (RPR) is a nonspecific screening test for syphilis that detects anticardiolipin antibodies.

Question 13

Two weeks after undergoing an allogeneic skin graft procedure for extensive full-thickness burns involving his left leg, a 41-year-old man develops redness and swelling over the graft site. He has not had any fevers or chills. His temperature is 36°C (96.8°F). Physical examination of the left lower leg shows well-demarcated erythema and edema (acite graft rejection) around the skin graft site. The graft site is minimally tender and there is no exudate. Which of the following is the most likely underlying mechanism of this patient’s skin condition?

Answer 13

Th1 cell-induced macrophage activation is responsible for this patient’s acute graft rejection. This type IV hypersensitivity reaction is triggered by foreign antigens from the allogeneic skin graft, which incite host T-cell sensitization

Question 14

Two hours after undergoing allogeneic kidney transplantation for polycystic kidney disease, a 14-year-old girl has lower abdominal pain. Examination shows tenderness to palpation in the area the donor kidney was placed. Ultrasound of the donor kidney shows diffuse tissue edema. Serum creatinine begins to increase and dialysis is initiated. Which of the following is the most likely cause of this patient’s symptoms?

Answer 14

Hyperacute graft rejection is mediated by preformed cytotoxic antibodies against donor class I HLA molecules or donor blood group antigens (type 2 hypersensitivity reactions).

Question 15

This man has periorbital edema, symptoms of myositis, fever, and eosinophilia after consuming bear meat. This suggests the diagnosis of trichinellosis. Major basic protein plays an important role in defending against helminthic infections. The release of major basic protein in response to this patient’s infection is most likely a result of which of the following?

Answer 15

Antibody-dependent cell-mediated cytotoxicity is critical for defense against helminthic infections. IgE molecules coat pathogens and are subsequently recognized by Fc receptor-bearing granulocytes, including eosinophils. The interaction of the IgE molecule and the receptor stimulates the release of cytotoxic granules such as major basic protein, which ultimately leads to the destruction of the pathogen.

Question 16

A 38-year-old woman comes to the physician because of a 2-day history of a red, itchy, burning rash on her vulva. She has had three similar episodes over the last two years that have all self-resolved. Genitourinary examination shows a small area of erythema with an overlying cluster of vesicles on the inside surface of the vulva. Latent infection of which of the following is most likely responsible for this patient’s recurrent symptoms?

Answer 16

Latency and reactivation in the dorsal root ganglion of host sensory neurons is the mechanism underlying the recurrent symptoms seen in herpes simplex virus 1 and 2 infection.

Question 17

A 4-year-old girl is brought to the pediatrician because of throat pain for 2 days. She had frequent episodes of oral thrush as a baby and has been treated for vaginal yeast infection twice in the past year. Physical examination shows white patches on the tongue and palate. Scraping off the patches reveals erythematous oral mucosa with pinpoint bleeding. Leukocyte count is within normal range. Exposure to nitroblue tetrazolium turns the patient’s neutrophils dark blue. A deficiency in which of the following enzymes is the most likely cause of this patient’s recurrent infections?

Answer 17

Patients with myeloperoxidase deficiency are typically asymptomatic but can also develop recurrent Candida infections (e.g., oral thrush and vulvovaginal candidiasis) due to ineffective hypochlorous acid production during the oxidative burst. The nitroblue tetrazolium test is positive (normal) in these patients because NADPH oxidase function is intact and still able to reduce the dye to blue. The diagnosis is confirmed by genetic testing or immunohistochemical staining.

Question 18

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Immune System: Block 1

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1
A 12-year-old boy is brought to the emergency department by his mother because of progressive shortness of breath, difficulty speaking, and diffuse, colicky abdominal pain for the past 3 hours. Yesterday he underwent a tooth extraction. His father and a paternal uncle have a history of repeated hospitalizations for upper airway and orofacial swelling. The patient takes no medications. His blood pressure is 112/62 mm Hg. Examination shows edematous swelling of the lips, tongue, arms, and legs; there is no rash. Administration of a drug targeting which of the following mechanisms of action is most appropriate for this patient?
2
A previously healthy 29-year-old man comes to the emergency department because of burning with urination for several days. He has also had pain in the right ankle for 3 days and pain and swelling in the left knee for 1 day. Two weeks ago, he had several days of fever and bloody diarrhea, for which he was treated with antibiotics. Examination shows a small left knee effusion and bilateral conjunctival injection. Which of the following is the most likely additional finding in this patient?
3
A 34-year-old man comes to the physician for evaluation of a rash on the elbows for several months. A biopsy of the affected area shows a thinned stratum granulosum as well as retained nuclei and spongiotic clusters of neutrophils in the stratum corneum. This patient’s skin findings are most likely associated with which of the following conditions?
4
A 12-year-old girl is brought to the physician by her mother 2 hours after cutting her hand while playing in the yard. Examination of the right hand shows a 2-cm laceration on the thenar region of the palm with some surrounding tenderness and erythema. The right palm appears mildly swollen in comparison to the left. In response to this patient’s injury, the endothelial cells lining the blood vessels of the affected area express increased numbers of cellular adhesion molecules. Which of the following mediators is most likely directly responsible for the described change?
5
A 26-year-old man is brought to the emergency department because of abdominal pain, dizziness, shortness of breath, and swelling and pruritus of the lips, tongue, and throat for 1 hour. The symptoms began minutes after he started eating a lobster dinner. It is determined that his symptoms are due to surface crosslinking of IgE. This immunologic event most likely caused the release of which of the following?
6
A 26-year-old man comes to the emergency department for evaluation of burning with urination and purulent urethral discharge for the past 3 days. He is sexually active with multiple female partners. Several months ago he was diagnosed with urethritis caused by gram-negative diplococci and received antibiotic treatment with complete resolution of his symptoms. A Gram stain of the patient’s urethral discharge shows gram-negative intracellular diplococci. Which of the following properties of the infecting organism most contributed to the pathogenesis of this patient’s recurrent infection?
7
One week after starting amoxicillin for sinusitis, a 4-year-old girl is brought to the emergency department with fever, rash, and myalgia. She has been hospitalized multiple times for recurrent streptococcal pneumonia and meningitis. She appears tired. Examination shows a diffuse urticarial rash. Her antibiotic is discontinued. Which of the following is the most likely underlying mechanism for her recurrent infections?
8
Two weeks after undergoing allogeneic stem cell transplant for multiple myeloma, a 55-year-old man develops a severely pruritic rash, abdominal cramps, and profuse diarrhea. He appears lethargic. Physical examination shows yellow sclerae. There is a generalized maculopapular rash on his face, trunk, and lower extremities, and desquamation of both soles. His serum alanine aminotransferase is 115 U/L, serum aspartate aminotransferase is 97 U/L, and serum total bilirubin is 2.7 mg/dL. Which of the following is the most likely underlying cause of this patient’s condition?
9
A 72-year-old man comes to the physician with chills, nausea, and diffuse muscle aches for 3 days. His niece had similar symptoms 2 weeks ago and H3N2 influenza strain was isolated from her respiratory secretions. He received his influenza vaccination 2 months ago. His temperature is 38°C (100.4°F). A rapid influenza test is positive. Which of the following mechanisms best explains this patient’s infection despite vaccination?
10
An investigator studying immune response administers a 0.5 mL intradermal injection of an autoclaved microorganism to a study volunteer. Four weeks later, there is a 12-mm, indurated, hypopigmented patch over the site of injection. Which of the following is the most likely explanation for the observed skin finding?
11
A 1-year-old girl is brought to the physician for a well-child examination. She has no history of serious illness. She receives a vaccine in which a polysaccharide is conjugated to a carrier protein. Which of the following pathogens is the most likely target of this vaccine?
12
13
A 2-year-old boy is brought to the physician by his mother for evaluation of recurrent infections and easy bruising. He has been hospitalized 3 times for severe skin and respiratory infections, which responded to treatment with antibiotics. Examination shows sparse silvery hair. The skin is hypopigmented and there are diffuse petechiae. Laboratory studies show a hemoglobin concentration of 8 g/dL, leukocyte count of 3000/mm3, and platelet count of 45,000/mm3. A peripheral blood smear shows giant cytoplasmic granules in granulocytes and platelets. Which of the following is the most likely underlying cause of this patient’s symptoms?
14
A 28-year-old man comes to the physician because of a two-week history of progressively worsening fatigue, nausea, and right upper quadrant pain. He has a history of intravenous heroin use. Hepatitis B surface antigen, hepatitis B e antigen, and hepatitis B core antibodies are positive. Hepatitis B screening 2 months ago was negative for hepatitis B surface antigen, hepatitis B core antigen, and hepatitis B core antibodies. Further analysis of the hepatitis B core immunoglobulin is most likely to show which of the following properties?
15
A 26-year-old woman comes to the physician because of several days of fever, abdominal cramps, and diarrhea. She drank water from a stream 1 week ago while she was hiking in the woods. Abdominal examination shows increased bowel sounds. Stool analysis for ova and parasites shows flagellated multinucleated trophozoites. Further evaluation shows the presence of antibodies directed against the pathogen. Secretion of these antibodies most likely requires binding of which of the following?
16
A 4-year-old girl is brought to the physician because of diarrhea and vomiting for 5 days. Vaccinations are up-to-date. She appears pale and irritable. Her vital signs are within normal limits. Examination shows petechiae on her trunk and extremities. Abdominal examination shows diffuse abdominal tenderness with hyperactive bowel sounds. The remainder of the exam shows no abnormalities. Laboratory studies show: Hemoglobin 8 g/dL Leukocyte count 17,000/mm3 Platelet count 49,000/mm3 Serum Creatinine 1.6 mg/dL Lactate dehydrogenase 300 U/L Coagulation studies are normal. A peripheral blood smear is shown. Which of the following is the most likely underlying cause of these findings?
17
A 44-year-old man with HIV comes to the physician for a routine follow-up examination. He has been nonadherent with his antiretroviral medication regimen for several years. He appears chronically ill and fatigued. CD4+ T-lymphocyte count is 405/mm3. Further evaluation of this patient is most likely to show which of the following findings?
18
An investigator is conducting an experiment to develop a new drug against HIV infection. HIV-infected and uninfected CD4 T-cell lines are mixed in-vitro with a chemically modified synthetic peptide triazole complex. The complex is found to have a high binding affinity to the gp120 protein, irreversibly inhibiting its function and reducing CD4 T cell infection. Inhibition of which of the following steps of HIV infection is the most likely therapeutic effect of this experimental drug?
19
A 4-month-old boy is brought to the physician because of a painful lesion on his right leg. Yesterday, he received all of his scheduled childhood immunizations, including the second dose of the diphtheria, tetanus, and acellular pertussis vaccine, which was administered in the right quadriceps. Physical examination shows a 2-cm ulcer with surrounding induration over the right anterolateral thigh. A skin biopsy of the lesion shows localized edema, skin necrosis, neutrophilic infiltration, and complement deposition. Which of the following is the most likely cause of his symptoms?
20
A 60-year-old man comes to the office because of an 8-month history of cough, night sweats, shortness of breath, and fatigue. He has also had a 9-kg (19.8-lb) weight loss during this time. He appears pale. Abdominal examination shows hepatosplenomegaly. His leukocyte count is 80,000/mm3 and his leukocyte alkaline phosphatase level is increased. A peripheral blood smear shows > 82% neutrophils with band forms and immature and mature neutrophil precursors. An x-ray of the chest shows a 9-mm right hilar nodule. Which of the following is the most likely cause of this patient’s laboratory findings?
21
A 3-year-old boy is brought to the physician for the evaluation of recurrent skin lesions. The lesions first appeared at the age of 3 months. He has also had several episodes of respiratory tract infections, enlarged lymph nodes, and recurrent fevers since birth. The boy attends daycare. His immunizations are up-to-date. He is at the 5th percentile for height and 10th percentile for weight. He appears ill. Temperature is 38.0°C (100.4°F). Examination shows several raised, erythematous lesions of different sizes over the face, neck, groin, and extremities; some are purulent. Bilateral cervical and axillary lymphadenopathy are present. Which of the following is the most likely underlying mechanism of this patient’s symptoms?
22
A 23-year-old man comes to the physician because of a 1-week history of anorexia, nausea, upper abdominal pain, and dark-colored urine. He recently returned from a trip to Belize. His temperature is 38.3°C (100.9°F). Physical examination shows scleral icterus and tender hepatomegaly. Serum studies show markedly elevated transaminases and anti-hepatitis A virus antibodies. In this patient, infected cells express more MHC class I molecules on their surfaces. This cellular event is primarily induced by a molecule that is also responsible for which of the following changes?
23
A 22-year-old man comes to the physician because of abdominal pain, diarrhea, and weight loss that started after a recent backpacking trip in Southeast Asia. He does not smoke or drink alcohol. His leukocyte count is 7,500/mm3 (61% segmented neutrophils, 13% eosinophils, and 26% lymphocytes). Stool microscopy shows rhabditiform larvae. This patient is most likely to develop which of the following?
24
An 8-year-old girl is brought to the emergency room for a 6-hour history of fever, sore throat, and difficulty swallowing. Physical examination shows pooling of oral secretions and inspiratory stridor. Lateral x-ray of the neck shows thickening of the epiglottis and aryepiglottic folds. Throat culture with chocolate agar shows small, gram-negative coccobacilli. The patient’s brother is started on the recommended antibiotic for chemoprophylaxis. Which of the following is the primary mechanism of action of this drug?
25
A 2-month-old boy is brought to the pediatrician for a routine check-up. His mother says he is feeding well and has no concerns. He is at the 85th percentile for height and 82nd percentile for weight. Immunizations are up-to-date. Results of serum hepatitis B surface IgG antibody testing are positive. Which of the following best explains this patient’s hepatitis B virus status?
26
A 1-year-old girl is brought to the physician for follow-up examination 1 week after admission to the hospital for bacterial pneumonia. She has had multiple episodes of purulent otitis media and infectious diarrhea since the age of 6 months. She underwent treatment for oral thrush 1 month ago. There is no family history of serious illness. Her height and weight are both below the 10th percentile. Physical examination shows no visible tonsils and slightly decreased breath sounds in the left lower lobe. Laboratory studies show increased deoxyadenosine concentration in both the serum and urine. An x-ray of the chest shows an absent thymic shadow. Which of the following additional findings is most likely in this patient?
27
A 42-year-old woman comes to the physician because of a 2-week history of joint pain and fatigue. She has a history of multiple unprovoked deep vein thromboses. Physical examination shows small bilateral knee effusions and erythematous raised patches with scaling and follicular plugging over the ears and scalp. Oral examination shows several small ulcers. Further evaluation of this patient is most likely to show which of the following?
28
Two weeks after undergoing an allogeneic skin graft procedure for extensive full-thickness burns involving his left leg, a 41-year-old man develops redness and swelling over the graft site. He has not had any fevers or chills. His temperature is 36°C (96.8°F). Physical examination of the left lower leg shows well-demarcated erythema and edema around the skin graft site. The graft site is minimally tender and there is no exudate. Which of the following is the most likely underlying mechanism of this patient’s skin condition?
29
Two hours after undergoing allogeneic kidney transplantation for polycystic kidney disease, a 14-year-old girl has lower abdominal pain. Examination shows tenderness to palpation in the area the donor kidney was placed. Ultrasound of the donor kidney shows diffuse tissue edema. Serum creatinine begins to increase and dialysis is initiated. Which of the following is the most likely cause of this patient’s symptoms?
30
A 31-year-old man comes to the physician because of severe muscle pain and fever for 4 days. He likes to go hunting and consumed bear meat 1 month ago. Examination shows periorbital edema and generalized muscle tenderness. His leukocyte count is 12,000/mm3 with 19% eosinophils. The release of major basic protein in response to this patient’s infection is most likely a result of which of the following?
31
A 38-year-old woman comes to the physician because of a 2-day history of a red, itchy, burning rash on her vulva. She has had three similar episodes over the last two years that have all self-resolved. Genitourinary examination shows a small area of erythema with an overlying cluster of vesicles on the inside surface of the vulva. Latent infection of which of the following is most likely responsible for this patient’s recurrent symptoms?
32
A 4-year-old girl is brought to the pediatrician because of throat pain for 2 days. She had frequent episodes of oral thrush as a baby and has been treated for vaginal yeast infection twice in the past year. Physical examination shows white patches on the tongue and palate. Scraping off the patches reveals erythematous oral mucosa with pinpoint bleeding. Leukocyte count is within normal range. Exposure to nitroblue tetrazolium turns the patient’s neutrophils dark blue. A deficiency in which of the following enzymes is the most likely cause of this patient’s recurrent infections?
33
A 27-year-old woman comes to the physician because of a 3-day history of a sore throat and fever. Her temperature is 38.5°C (101.3°F). Examination shows edematous oropharyngeal mucosa and enlarged tonsils with purulent exudate. There is tender cervical lymphadenopathy. If left untreated, which of the following conditions is most likely to occur in this patient?
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0h 22m

Session
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Question

A 27-year-old woman comes to the physician because of a 3-day history of a sore throat and fever. Her temperature is 38.5°C (101.3°F). Examination shows edematous oropharyngeal mucosa and enlarged tonsils with purulent exudate. There is tender cervical lymphadenopathy. If left untreated, which of the following conditions is most likely to occur in this patient?

Answer 18

Dilated cardiomyopathy is a potential late and serious complication of acute rheumatic fever, a type II hypersensitivity reaction that can occur within 2–4 weeks after untreated GAS pharyngitis. Rheumatic heart disease can manifest in several ways, including myocarditis, pericarditis, and valvular disease (mitral valve involvement is the most common). The development of dilated cardiomyopathy is multifactorial and usually occurs secondary to valvular disease, but can also result directly from myocarditis.