Micro USMLE 8-21 & 8-26(6) Flashcards
A transplant patient presents with a fever, decreased SpO2, shortness of breath, non-productive cough, nausea, vomiting, and tachypnea. Because of these symptoms and her transplant history, she should be suspected of having cytomegalovirus (CMV) pneumonitis, which is a common complication in immunocompromised patients after receiving a lung transplant, solid organ transplant or a bone marrow transplantation and occurs typically 1-4 months post-transplant.
Radiographic manifestations of CMV pneumonia are most commonly seen as bilateral, symmetrical, peribronchovascular, and alveolar processes occurring predominantly in the lower lobes, as in this patient. However, it can cause a focal consolidation or a solitary pulmonary nodule, but this is more suggestive of a ?
bacterial or fungal infection. Histopathology shows large cells with intranuclear basophilic inclusions (?owl’s eyes?—see black arrow in image below) and are pathognomonic of CMV infection. CMV is an enveloped, double stranded linear DNA virus that is latent in mononuclear cells. This patient’s history as well as radiographic and histologic findings make CMV the most likely causative organism.
Non-enveloped and double stranded linear DNA are characteristics of adenovirus, which causes respiratory involvement in immunocompromised patients and has a similar histologic presentation as CMV; however, adenovirus is far less common than CMV. Fluconazole is the drug of choice for candida albicans, which can infect immunocompromised patients; however, it rarely involves the respiratory tract and is seen histologically as budding cells with pseudohyphae. Cowdry type A inclusion bodies are pathognomonic for Herpes simplex virus (HSV), which is known to manifest in immunocompromised patients; however, it does not involve the respiratory tract. Langhans giant cells are associated with granulomas caused by ?
mycobacterium tuberculosis, which does affect immunocompromised patients; however, it’s typically seen radiographically with apical lung involvement and symptoms of hemoptysis. Multiple ring enhancing lesions on MRI are associated with toxoplasma gondii, which is known to infect immunocompromised patients causing brain abscesses; however, it does not invade the respiratory tract.
Cytomegalovirus (CMV) is an enveloped double stranded linear DNA virus that is latent in mononuclear cells. It is seen histologically as large cells with intranuclear inclusions (“owl′s eyes”) and is a common cause of ?
pneumonia in immunocompromised patients, especially those 1-4 months post-transplant.
This patient presents with fever, chills, and malaise, along with a tender axillary lymph node. Significantly, the patient notes that he was bitten by a flea during a visit to New Mexico, and his lab test results indicate disseminated intravascular coagulation (DIC). This clinical picture is most suggestive of infection with Yersinia pestis. Y pestis is the organism responsible for the bubonic plague (ie, Black Death).
Y pestis is spread to humans by fleas from rodents, especially prairie dogs, in the western United States. This rare disease develops after 2–8 days of incubation and is characterized by the presence of exquisitely tender lymph nodes called buboes (hence, the name bubonic plague). When Y pestis enters the bloodstream, it can lead to ?
abscess formation, DIC, and necrosis of the digits. This patient’s prolonged prothrombin time (PT) and partial thromboplastin time (PTT), low platelet count and fibrinogen level, and elevated D-dimer level support a diagnosis of DIC. He was appropriately escalated to inpatient care and given the appropriate antibiotic therapy, streptomycin and tetracycline.
The patient’s singular, painful, dark ulcer would be consistent with leishmaniasis, but cutaneous leishmaniasis is not transmitted in the United States and never causes systemic illness. This patient’s painful ulcer surrounded by hemorrhagic purpura is inconsistent with the ulcer caused by Bacillus anthracis, which is painless and accompanied by swelling out of proportion to its size. Infection with Sporothrix schenckii also typically presents as a painless ulcer but has a more indolent clinical course without systemic involvement in most patients and is associated with?
soil and plant exposure. Babesiosis (caused by Babesia microti) does not present with a dark ulcer at the bite site and tender lymphadenopathy; instead, it presents with fever and signs of anemia (eg, fatigue, pallor).
Yersinia pestis is transmitted by fleas from a rodent reservoir and causes exquisitely painful lymphadenopathy, a painful ulcer with surrounding hemorrhagic purpura, sepsis, and disseminated intravascular coagulation. Although most cases of plague occur in parts of Africa and Asia, a travel history to the western United States is also a risk factor for?
Y pestis infection.
This patient has a fever and a pruritic, vesicular rash with macules, papules, and pustules in different stages of healing. This is a classic case of chickenpox, which is caused by varicella-zoster virus (VZV). VZV is a highly contagious herpesvirus that is transmitted by respiratory droplets or direct contact and produces a self-limited infection. Following an infection, reactivation of latent VZV in the dorsal root ganglia can cause herpes zoster (shingles). Shingles is a sporadic disease characterized by a unilateral vesicular eruption within a dermatome, as shown, and is often associated with severe pain. Patients with herpes zoster can transmit their infection to seronegative individuals, who will then develop ?
chickenpox.
The other answer options are manifestations associated with other infections.
Autoimmune hemolytic anemia can be associated with conditions that may also cause rashes, but not the vesicular, pruritic rash seen in this patient.
Congenital deafness is more often attributed to maternal rubella or cytomegalovirus infections. Although rubella causes a widespread rash, it is not pruritic, and it would cause congenital deafness in a child only if seen in the mother during pregnancy.
Orchitis is more commonly associated with mumps infection, which manifests with inflammation of one or both parotid glands.
Subacute sclerosing panencephalitis is a complication of measles infection, which causes a widespread rash, but that is not pruritic.
Varicella-zoster virus (VZV) is in the herpesvirus family and is responsible for causing chickenpox and herpes zoster, or shingles. Chickenpox is transmitted by respiratory droplets and produces a self-limited infection that causes a pruritic, vesicular rash. Herpes zoster is caused by reactivation of latent VZV in the dorsal root ganglia and causes a ?
painful unilateral vesicular eruption within a dermatome.
This patient is admitted to the hospital in status asthmaticus, and mechanical ventilation is initiated after he experiences acute respiratory failure. After 96 hours, the patient requires additional ventilatory support. He has also developed a fever and tracheobronchial secretions. X-ray of the chest reveals a right lower lobe infiltrate. This patient likely has ventilator-associated pneumonia (VAP), a common complication among patients requiring ventilation. Sedative medications required during intubation depress the native ciliary elevator function of natural respiration, leading to VAP. Symptoms include fever or hypothermia, new purulent sputum, or a change in respiratory support requirements. In order for VAP to be diagnosed, a patient must have been receiving mechanical ventilation for at least 48 hours. Both chronic lung disease and convalescence in the intensive care unit are risk factors for VAP. It is often caused by the gram-negative bacillus Pseudomonas aeruginosa. For this reason, empiric antibiotic therapy for ?
VAP, such as piperacillin-tazobactam, must be prescribed to cover Pseudomonas.
Legionella pneumophila is a cause of a typical pneumonia syndrome that presents with cough, high fever, hyponatremia, and diarrhea. Candida albicans causes skin, vaginal, and oropharyngeal infections but is a very rare cause of pneumonia. Clostridium difficile presents with diarrhea in the setting of recent antibiotic use. Staphylococcus epidermidis is a cause of urinary tract infections and infections in indwelling prosthetic devices, intravenous lines, and Foley catheters.
Sedative medications required for intubation can cause depression of native ciliary elevator function of natural respiration. This increases a patient’s susceptibility to certain respiratory pathogens and can lead to VAP. P. aeruginosa is the organism most commonly associated with ?
VAP
This patient presents with urethritis and a purulent discharge, symptoms that are characteristic of infection with Neisseria gonorrhoeae in a man. A Gram stain showing gram-negative diplococci within neutrophils (pictured above) is sufficient for a diagnosis of gonorrhea in male patients. The same is not true for the presence of gram-negative organism in a female sample because non-pathogenic (commensal) Neisseria comprise part of the normal vaginal flora and would be present absent a gonococcal infection.
N. gonorrhoeae have specialized antigenically variable pili that mediate its attachment to mucosal surfaces. These surface-associated pili vary continually so that an effective immune response cannot be mounted. This is the reason?
why individuals can be repeatedly infected.
The ability to metabolize urea into ammonia and carbon dioxide is characteristic of Ureaplasma urealyticum, which causes nongonococcal urethritis. A life cycle involving an extracellular infectious form and intracellular replicative form is specific for Chlamydia trachomatis. Treponema pallidum, which causes syphilis, has a helical shape with two cell membranes and flagella trapped between these two membranes (endoflagella). Neisseria meningitidis causes meningitis and has a polysaccharide capsule with the ability to ferment maltose.
Urethritis and a purulent urethral discharge point toward an infection with Neisseria gonorrhoeae, a gram-negative diplococcus with antigenically variable pili that mediate its virulence in the human host. There is a high incidence of?
comorbid gonococcal and chlamydial infections.
For an HIV-infected patient, findings of fever, headache, altered mental status, vision changes, and an elevated opening pressure on lumbar puncture should raise concerns for an infectious intracranial process. In a patient who is noncompliant with medications and has had exposure to pigeon droppings (based on her gardening in a park), the primary concern is Cryptococcus neoformans meningoencephalitis. C. neoformans meningoencephalitis is acquired by inhaling dust from soil contaminated with bird droppings, particularly those of pigeons. This is an AIDS-defining illness, because it generally does not occur until the CD4+ cell count is <50. Under the microscope, Cryptococcus appears as a heavily encapsulated nondimorphic yeast with narrow-based budding on India ink stain (as shown in this image).
Broad-based budding yeast refers to Blastomyces. Blastomyces is found in wooded areas east of the Mississippi River.
Budding yeast with pseudohyphae refers to?
Candida albicans, which can cause thrush, vulvovaginitis, and numerous other mucocutaneous infections.
Mold with hyphae that branch at 45-degree angles refers to Aspergillus fumigatus, which more commonly infects individuals with underlying pulmonary disease or those working in construction (due to inhalation exposure).
Small intracellular yeast refers to Histoplasma, a fungus found in the Mississippi and Ohio River valleys.
In a patient with HIV infection, neurologic symptoms, and an increased opening pressure on lumbar puncture suggest meningoencephalitis due to infection with Cryptococcus neoformans. Cryptococcus is an encapsulated yeast with ?
narrow-based budding, and cryotococcosis is an AIDS-defining illness.
This patient, who has been experiencing vaginal itching for the past week, is found to have greenish vaginal discharge and a friable cervix, a presentation that suggests a diagnosis of trichomoniasis, a sexually transmitted infection (STI). Three million Trichomonas infections are diagnosed annually in the United States. Although both women and men may be infected, men have no symptoms. All sexual partners of the infected patient must be treated with metronidazole. Trichomonas vaginalis is typically seen as flagellated trophozoites on a wet mount. Polymerase chain reaction (PCR) may also be used to identify the organism. Because the frequency of mixed STIs is relatively high, the finding of motile protozoa means ?
further workup is needed.
Fuzzy epithelial cells, or clue cells, would be indicative of bacterial vaginosis caused by overgrowth of Gardnerella relative to other normal vaginal flora, but Gardnerella infection would not cause a friable cervix. Gram-negative diplococci would most likely be indicative of gonorrhea, which causes a mucopurulent, rather than a watery, discharge. Gram-positive cocci in the genitourinary context are most likely Staphylococcus saprophyticus, which can cause urinary tract infections, but not vaginitis. Spores and hyphae-like growth on Giemsa stain would indicate a candidal (yeast) infection, which presents with thick, cottage cheese–like discharge.
