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USMLE STEP 1, 2, 3 > Internal Medicine_Infectious Diseases_6 > Flashcards

Internal Medicine_Infectious Diseases_6 Flashcards

Bacteria_Mycobacteria (TB, leprosy, etc.)

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USMLE® Step 1 flashcards
1
Q
A
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2
Q

What type of stain is used to identify Mycobacterium tuberculosis?

A

Ziehl-Neelsen stain with carbol fuchsin (acid-fast stain).

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3
Q

What medium is used to culture Mycobacterium tuberculosis?

A

Lowenstein-Jensen agar.

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4
Q

What is the major virulence factor of M. tuberculosis that prevents phagosome-lysosome fusion?

A

Sulfatides.

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5
Q

Which virulence factor of M. tuberculosis contributes to granuloma formation and evasion of macrophages?

A

Cord factor.

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6
Q

What are the primary symptoms of reactivation tuberculosis?

A

Cough, night sweats, hemoptysis, anorexia, and weight loss.

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7
Q

What is the common radiologic finding in primary tuberculosis?

A

Ghon complex (calcified lung lesion and nearby lymph node).

basically bihilar LAD.

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8
Q

What is the hallmark of miliary TB?

A

Hematogenous dissemination leading to millet seed-like lesions.

can lead to organ failure and septic shock
millet seed-like lesions in lungs
can involved bones, adrenal glands, CNS, and GU (sterile pyuria)

diagnosis is with acid fast blood cultures and tissue biopsy (culture/NAA)

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9
Q

What is the treatment regimen for active tuberculosis?

A

RIPE: Rifampin, Isoniazid, Pyrazinamide, and Ethambutol.

4 months of isoniazid (plus B6) and rifampin.

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10
Q

What are the major risk factors for reactivation of latent tuberculosis?

A

HIV, immunosuppression, and TNF-alpha inhibitor therapy.

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11
Q

What extrapulmonary condition is associated with TB of the spine?

A

Pott disease.

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12
Q

What diagnostic test is used to screen for TB and involves an intradermal injection?

A

Purified protein derivative (PPD) skin test.

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13
Q

A PPD is considered positive in those with high risk of TB if the induration size is >

A

5 mm

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14
Q

Who are considered high risk individuals for TB?

A

HIV, recent TB contact, immunocompromised, transplant recipients, evidence of prior TB infection (lung calcification, fibrosed regions, nodular regions).

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15
Q

The PPD may be false-negative in patients with

A

CD4+ counts < 200/mm3 (HIV)

Sarcoidosis

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16
Q

A PPD is considered positive in those with intermediate risk of TB if the induration size is >

A

10 mm

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17
Q

Who are considered moderate risk individuals for TB?

A

Recent immigrants (<5 years) from TB-endemic areas
Injection drug users
Residents & employees of high-risk settings (eg, prisons, nursing homes, hospitals, homeless shelters)
Mycobacteriology laboratory personnel
Higher risk for TB reactivation (eg, diabetes, prolonged corticosteroid therapy, leukemia, end-stage renal disease, chronic malabsorption syndromes)
Children age <4, or those exposed to adults in high-risk categories

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18
Q

A PPD is considered positive in those with normal risk of TB if the induration size is >

A

15 mm

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19
Q

When is a PPD recommended as part of prenatal care?

A

The PPD skin test is only indicated in pregnant women with one or more of the following risk factors: known case of HIV infection, close contact with individuals suspected of having tuberculosis, immigration from a highly endemic region, homelessness, living or working in prisons or mental health care facilities, certain non-infectious diseases that increase the risk of tuberculosis (e.g. diabetes mellitus, cancer, alcohol use disorder, intravenous drug use).

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20
Q

(+) PPD with (-) X-ray is managed with … ?

A

Isoniazid for 9 months

other forms of treatment for latent TB:
Isoniazid and rifapentine for 3 months or rifampin for 4 months

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21
Q

active TB (RIPE) is managed with … ?

A

2 months of RIPE: Rifampin, Isoniazid, Pyrazinamide, and Ethambutol

and

4 months of isoniazid and rifampin

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22
Q

Following a (+) PPD, first order what diagnostic test?

A

a chest x-ray

differentiates between active and latent TB

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23
Q

In the United States, a PPD is considered negative in healthy patients with low likelihood of TB if the induration size is <

A

15 mm

the cutoff for intermediate-risk patients (e.g. healthcare workers, recent immigrants) is < 10 mm

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24
Q

Why should individuals who are to be started on a TNF-α inhibitors (e.g. infliximab) receive a PPD test?

A

Inhibition of TNF-α via immunosuppression drugs causes lack of TNF-α –> lack of granuloma –> lack of containment of tuberculosis –> resultant reactivation of tuberculosis

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25
Q

Interferon-γ release assay (IGRA) has (greater/fewer) false positives from BCG vaccination than PPD testing?

A

fewer

IFN-γ release assay tests cell mediated response by seeing if macrophages release IFN-γ when presented with antigen.

These assays don’t get false positives from patients who are BCG vaccinated, thus are the preferred methods of testing for these patients.

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26
Q

Is Interferon-γ release assay (IGRA) is influenced by prior BCG vaccination?

A

No

If someone has prior BCG vaccination, performing a PPD test is not appropriate given the high false-positive rate in such individuals

Regardless, you interpret the PPD screen ignoring the fact that the patient has had a BCG vaccine.

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27
Q

Isoniazid can be given as a monotherapy for tuberculosis ONLY when there is a(n)

A

positive PPD and a negative chest x-ray

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28
Q

What is the next step in management for a healthy patient with 16-mm induration at 48 hours following PPD testing, normal chest X-ray, and no acid-fast bacilli?

A

9 months of isoniazid and pyridoxine (B6)

29
Q

What is the next step in management for an asymptomatic patient that has a 12-mm induration two days after a PPD injection? The patient has no TB risk factors.

A

No additional intervention required

in the US, an induration size of < 15 mm is considered negative in healthy patients with low likelihood of TB

30
Q

What is the next step in management for an HIV patient who has an 8-mm induration at 48 hours following PPD testing and a normal chest X-ray?

A

9 months of Isoniazid and pyridoxine (B6)

this patient should be treated for latent TB (> 5 mm)

31
Q

What type of hypersensitivity reaction is tuberculin skin test (PPD)?

A

Type IV HSR (Th1 Mediated)

32
Q

What can be used besides CXR for active TB infection

A

Sputum cultures taken at various times

Test with AFB smear, mycobacterium culture and NAA test

33
Q

What is seen on CXR for patients with a primary TB infection?

A

hilar lymphadenopathy

patients are usually asymptomatic with possibly fever, cough, and fatigue

34
Q

primary TB infection is typically diagnosed with … ?

A

PPD of IFN y release

35
Q

Reactivation of TB tends to present with what symptoms?

A

fever, night sweats, dyspnea, weight loss, cough (hemoptysis)

36
Q

Reactivation of TB has what characteristic CXR?

A

pulmonary infiltrate in the upper lobe

diagnosis should be with CXR and sputum.

37
Q

when can a patient come out of isolation while being treated for TB?

A

after 2 weeks on medication and improving

with

3 consecutive AFB smears

38
Q

What is the characteristic temperature preference for Mycobacterium leprae?

A

Cooler temperatures, often affecting the skin and extremities.

39
Q

What type of stain is used to identify Mycobacterium leprae?

A

Acid-fast stain, specifically using carbol fuchsin (Ziehl-Nelson).

High concentration of mycolic acid.

40
Q

What is the main non-human reservoir for Mycobacterium leprae in the United States?

A

Armadillos (rarely).

Primarily transmitted through respiratory droplets from infected people.

41
Q

What type of immune response is associated with tuberculoid leprosy?

A

A strong TH1 cell-mediated immune response.

It leads to the containment of the bacteria within macrophages.

42
Q

How does tuberculoid leprosy typically present on the skin?

A

As well-demarcated, slightly elevated, hypopigmented, hairless, hypoesthetic skin macules or plaques.

43
Q

What type of immune response is predominant in lepromatous leprosy?

A

A TH2 humoral immune response.

The TH2 response leads to failed containment of the bacteria, leading to dissemination of the bacteria to various parts of the body.

Leads to a higher risk of human-to-human transmission.

44
Q

What are the common neurological manifestations of lepromatous leprosy?

A

“Glove and stocking” neuropathy, with sensory loss in the extremities.

Palpable nerves with neuropathy.

Characterized by loss of sensitivity to temperature and pain in the extremities

45
Q

What is the facial deformity commonly seen in advanced lepromatous leprosy?

A

Leonine facies.

Thickening of the skin, loss of eyebrows and eyelashes, nasal collapse, and nodular earlobes.

46
Q

What is the treatment regimen for tuberculoid leprosy?

A

Dapsone and rifampin for 6-24 months.

47
Q

What is the treatment regimen for lepromatous leprosy?

A

Dapsone, rifampin, and clofazimine for 2-5 years.

48
Q

How is lepromatous leprosy transmitted between humans?

A

Through prolonged, close contact over many months.

49
Q

What test can differentiate tuberculoid from lepromatous leprosy?

A

Tuberculoid leprosy presents with well-demarcated, hairless plaques, while lepromatous leprosy presents with poorly demarcated raised lesions.

The lepromin skin test (positive in tuberculoid leprosy, negative in lepromatous leprosy).

50
Q

Lepromatous leprosy is associated with what type of immune system?

A

A weaker immune response.

These infections have a more widespread lesions, and a higher bacterial load.

51
Q

What are the two distinct clinical presentations of M. leprae infection?

A

Tuberculoid leprosy

and

Lepromatous leprosy.

52
Q

What is the diagnostic tool to classify the type of leprosy in a person already diagnosed with the disease?

A

The lepromin skin test.

Inactivated Mycobacterium leprae is injected under the skin.

It is a diagnostic tool to classify the type of leprosy in a person already diagnosed with the disease. A positive result, where a nodule forms, indicates a stronger cellular immune response, typically seen in tuberculoid leprosy. A negative result, where no nodule forms, indicates lepromatous leprosy, which is associated with a weaker immune response, more widespread lesions, and a higher bacterial load.

53
Q

How does tuberculoid leprosy typically present on the skin?

A

Lepromatous leprosy often manifests with poorly demarcated diffuse hypopigmented erythematous papules, macules, nodules, and plaques.

54
Q

How is leprosy diagnosed?

A

skin biopsy with an acid fast stain.

55
Q

What stain is used to detect acid-fast mycobacteria such as Mycobacterium avium complex (MAC)?

A

Carbol fuchsin stain.

56
Q

Why are mycobacteria acid-fast?

A

Due to their high mycolic acid content in the cell wall.

57
Q

What immune system feature do mycobacteria evade by forming granulomas?

A

They invade macrophages and form granulomas to escape immune detection.

58
Q

What does MAC stand for in nontuberculous mycobacteria?

A

Mycobacterium avium complex (M. avium and M. intracellulare).

59
Q

What are the TB-like symptoms caused by MAC infections?

A

Cough, fatigue, night sweats, shortness of breath, and weight loss.

60
Q

MAC generally causes pulmonary disease in patients with …. ?

A

HIV
COPD
Bronchiectasis

61
Q

In which immunocompromised population is disseminated MAC disease common?

A

Patients with advanced HIV and a CD4 count <50.

62
Q

What is the recommended treatment for MAC infections?

A

A macrolide (e.g., clarithromycin or azithromycin)

combined with

ethambutol and rifabutin

63
Q

What is the prophylactic treatment for HIV patients with CD4 counts <50 who are not on ART?

A

A macrolide (e.g., azithromycin) and initiation of ART.

64
Q

What skin condition is commonly caused by Mycobacterium marinum in aquarium handlers (fresh and salt water)?

A

Skin infections.

65
Q

What infection is caused by Mycobacterium scrofulaceum, most commonly in children?

A

Cervical lymphadenitis.

66
Q

How is Mycobacterium marinum typically transmitted?

A

Through direct contact with contaminated water or infected animals like fish.

67
Q

Mycobacterium marinum is treated with …. ?

A

Clarithromycin

with

ethanmbutol or rifampin

68
Q

Infection with Mycobacterium ______ can also mirror TB.

A

Mycobacterium kansaii

USMLE STEP 1, 2, 3 (45 decks)

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