Week 11 Flashcards
12 yr old w/ pain in right knee, high BP, subcutaneous nodules, hx of pharyngitis 3 wks ago, cardiac exam with diastolic murmur
- Serological testing is positive for streptolysin O and DNase B. Describe the pathogenesis of this child’s acute disease.
- If the patient had presented to his pediatrician three weeks ago for evaluation of his pharyngitis, discuss the laboratory tests that could have been ordered to identify the causative organism. Describe the expected findings of these tests for this organism.
- During work-up, the patient is also discovered to be oliguric with dark-brown colored urine. Urinalysis shows 3+ blood and 1+ protein, and microscopic analysis reveals dysmorphic red blood cells (RBCs) and RBC casts. Describe the mechanism of injury and the microscopic changes you would expect to see in the patient’s kidney.
- The patient has acute rheumatic fever (ARF), based upon the presence of polyarthritis, subcutaneous nodules, and confirmatory serologic testing. ARF is an immune-mediated sequela of pharyngitis caused by group A beta-hemolytic Streptococcus. ARF results when antibodies and CD4+ T cells directed against streptococcal M proteins cross-react with cardiac self-antigens. As a result, antibody binding activates complement, recruits inflammatory cells (neutrophils, macrophages), and results in cytokine production. Thus, damage to affected organs (heart, joint, skin) is caused by a combination of antibody- and T-cell mediated reactions.
- Gram stain results would reveal Gram-positive cocci in chains. Differential biochemical tests indicate that the organism is catalase-negative and PYR-positive. Culture results indicate the organism is bacitracin sensitive and displays β-hemolysis on blood agar plates. Antigen detection tests can be performed for detection of the Group A antigen.
- Post-streptococcal glomerulonephritis (or acute proliferative glomerulonephritis) occurs secondary to glomerular deposition of antigen/antibody complexes (usually formed by antibodies attaching to bacterial particles planted in the glomerulus). The tissue response includes mesangial proliferation and recruitment of inflammatory cells to the site of injury, both of which are seen on microscopic examination (enlarged, hypercellular glomerular tufts).
15 yr old w/ fever, chills, worsening dyspnea, productive cough, with tenacious yellowish sputum, Chest radiographs show extensive infiltrates in the left lower lung involving both the lower lobe and the lingula. Blood and sputum are taken for cultures followed by assays for drug susceptibility tests.
- Discuss which laboratory tests could be used to confirm the most likely causative organism and describe the expected findings for this organism.
- Identify and categorize this patient’s pneumonia syndrome based on the presence or absence of distinguishing patient history and physical examination features.
- Gram stain of sputum shows the organism grows as Gram-positive diplococci (or cocci in short chains). Differential biochemical tests indicate that the organism is catalase-negative and PYR-positive. Culture results indicate the organism is optochin susceptible, displays α-hemolysis on blood agar plates, is bile-esculin negative on bile esculin agar plates, and displays a positive Quellung reaction
- This patient has Community-Acquired Pneumonia. There are no special history or examination features that would indicate an atypical course (which would be suggested by an insidious course, prolonged duration of symptoms, and decreased severity of symptoms). His symptoms have instead been acute onset and severe with a high fever. There are no historical elements that would suggest a recent hospital visit, longer hospital admission, other recent or regular medical interactions, or immunocompromise.
Explain why the presence of beta-lactamases changes the course of treatment, and include an appropriate treatment.
- The β-lactamase enzyme produced by the bacteria breaks the beta-lactam ring of penicillin via hydrolysis deactivating the drug’s antibacterial properties.
- An appropriate treatment is a penicillinase-resistant penicillin including members of the isoxazolyl penicillin family such as cloxacillin, dicloxacillin, or oxacillin. They were synthesized to counter the increasing prevalence of infections caused by penicillin-resistant Staphylococcus aureus. Another potential treatment option is to combine a β-lactamase inhibitor such as tazobactam or clavulanic acid with penicillin to overcome the β-lactamase-mediated antibiotic resistance which otherwise inactivates most penicillins. Additionally, it would be also be appropriate to change the antibiotic to a subclass related to beta-lactams, but lack sensitivity to β-lactamases, such as a third-generation cephalosporin (e.g., ceftriaxone).
22 y/o female presents primary care physician with three days of increased urinary frequency and suprapubic pain after micturition. She denies fever, chills, flank pain, nausea/vomiting, or vaginal discharge. She denies any similar episodes in the past. She is sexually active and states that her partner consistently uses condoms. She has no history of sexually transmitted diseases. Physical examination reveals suprapubic tenderness to palpation but is otherwise unremarkable. Spot urinary pregnancy test is negative. Dipstick urinalysis is significant for WBC 3+, RBC 1+, and positive nitrite, and the urine sample is sent for culture.
- Identify the most likely family of organisms responsible, as well as the most common causative pathogen for this patient’s signs and symptoms.
- Outline the expected screening OSE findings for this patient’s clinical condition.
- The patient’s physician recommends integrative approaches to reduce her risk of future urinary tract infections (UTIs).
- The detection of nitrite on urinalysis reflects the presence of a gram-negative bacilli from the Enterobacteriaceae family, which convert urinary nitrate to nitrite. Escherichia coli is the most common microbial cause of simple cystitis (75 to 95% of cases), with occasional infections caused by other species of Enterobacteriaceae (such as Klebsiella pneumoniae and Proteus mirabilis; and less frequently Serratia marcescens)
- In this patient with acute cystitis, we would expect OSE findings related to Viscerosomatic reflexes due to irritation of the bladder and lower ureter. Representing sympathetic Viscerosomatic reflexes, we would expect to find bilateral acute tissue texture changes and hypertonicity from T11-L2, Chapman’s reflexes anteriorly in the periumbilical area and posteriorly at the L2 Transverse processes. In addition, there may be some tissue texture changes and tenderness in the anterior abdomen 1 cm superior to the umbilicus representing the inferior mesenteric ganglion. Representing parasympathetic Viscerosomatic reflexes, we would expect to find tissue texture changes and sacral dysfunction from S2-4.
- The presumed active compounds in cranberry, proanthocyanidins (PACs), inhibit bacterial adhesion to the bladder wall and decrease bacterial virulence.D-mannose is ordinarily found in glycoproteins on the surface of uroepithelial cells, but pathogenic bacteria (such as E. coli) are able to use fimbriae to adhere to the D-mannose on the urinary epithelium. When taken as a supplement, on the other hand, D-Mannose is not metabolized in the blood and therefore concentrates in the bladder, where it binds to bacterial fimbriae and blocks the ability of bacteria to adhere to the epithelial cell wall.
A 45-year-old male who breeds parrots and other exotic birds complains of intermittent symptoms of malaise and shortness of breath. These symptoms tend to subside when he is away from work for a few days. A thorough workup including imaging, pulmonary function testing, bronchoalveolar lavage, and lung biopsy eventually leads to a diagnosis of hypersensitivity pneumonitis.
- Compare and contrast the expected findings in this disease with those of sarcoidosis regarding:
Presentation/symptoms
Imaging
- Compare and contrast the expected findings in this disease with those of sarcoidosis regarding:
Lymphocyte count and CD4/CD8 ratio in bronchoalveolar lavage fluid and Histologic changes
- After the patient fails to respond to a beta-lactam antibiotic, you suspect that he is infected with Legionella pneumophila even though cultures are negative for bacteria. Describe why the routine culture and Gram-stained specimen would be negative for Legionella organisms, then describe how this organism could be isolated and detected
- Hypersensitivity Pneumonitis (HP) patients tend to present with vague constitutional and respiratory symptoms associated with exposure to environmental antigens, which may resolve when the antigen is removed. Imaging findings in HP are nonspecific and tend to show diffuse nodular infiltrates with later or severe cases showing fibrosis; Sarcoidosis patients may also present with vague symptoms (or may be asymptomatic) but symptoms tend not to be related temporally to an identifiable exposure. In either disease, severe cases can present with more serious respiratory symptoms. Imaging findings in Sarcoidosis include hilar adenopathy and interstitial infiltrates that progress in a typical order depending upon the stage, and in late stages also include fibrosis.
- In both hypersensitivity pneumonitis (HP) and Sarcoidosis, increased lymphocytes are seen in bronchoalveolar lavage specimens. But in HP, the CD4/CD8 ratio tends to be near 1:1 whereas in Sarcoidosis the CD4 count tends to be much higher than the CD8 count. Histologically, both diseases are characterized by granulomatous changes. However, in Sarcoidosis, the granulomas are universally present and are well-formed. In HP, the granulomas are small and poorly formed, and may not be seen at all. More importantly, HP is characterized by interstitial inflammation which is not generally seen in Sarcoidosis.
- A Gram stain (as used in this case) is usually negative because the gram-negative rods are too thin to be seen in clinical specimens. This organism is usually best visualized with silver stain. In addition, the organism should be cultured on charcoal yeast extract media (supplemented with iron and cysteine) with extended incubation (at least 1-2 weeks). Because these bacteria require cysteine and iron salts for primary isolation, no growth will occur on blood or chocolate agars.
A 35-year-old male with a history of intravenous drug use and homelessness presents to a community health clinic with complaints of a dry persistent cough, fever, and anorexia. Over the preceding four weeks, he has unintentionally lost twelve pounds and has been experiencing chills and night sweats. Serologic testing for HIV infection reveals that the patient is HIV positive. A sputum sample is induced, collected, and submitted for bacterial, fungal, and mycobacterial cultures, as well as an acid-fast bacilli (AFB) smear and testing for Pneumocystis organisms.
- Compare the role and limitations of sputum culture to sputum AFB testing in the diagnostic work-up of this patient.
- Conventional culture is the most definitive tool for detection of TB (can detect as few as 10 bacteria/mL; the sensitivity and specificity of sputum culture are about 80% and 98%, respectively). Sputum culture is required for drug susceptibility testing and for species identification.
- However, culture may take at least a month to perform (because of the slow growth pattern of Mycobacteria) and depends on the burden of organisms, which may be lower in this HIV-infected patient.
- A sputum AFB smear is the most rapid and inexpensive test for TB.
- However, AFB testing is less sensitive than culture (~10,000 bacilli per mL are needed for detection using light microscopy; the sensitivity and positive predictive value are 45-80% and 50-80%, respectively). Because the organism burden is lower in the setting of HIV infection, the sensitivity of an AFB smear is further diminished in this patient (sensitivity may be as low as 20-30%).
Compare the role and limitations of IGRA to TST in the diagnostic evaluation of this patient.
I- GRA and TST (purified protein derivative / PPD) are rapid diagnostic tests which both have a relatively high sensitivity for diagnosing TB.
Regarding specificity, IGRA is considered relatively more specific (88-99%). This is because of the potential for false-positive tests with TST in patients sensitized to BCG or most nontuberculous mycobacteria (such as M. avium complex), which lowers TST’s specificity (85-86%) for ruling out TB. Neither IGRA or TST can be used in isolation to establish (or rule out) the diagnosis of TB, because a positive IGRA/TST only indicates a history of TB infection but cannot definitively distinguish between active and latent TB.
