Week 4: Clinical TB

Question 1

IGRAs: interferon gamma release assays

Answer 1

• single blood test

- no cross reaction to BCG and most NTMs except M africanum, M bovid, M kansasii, M marine, M szulgai

Question 2

Recognize NTM

Answer 2

• Morphotype: middle aged white females, slender, tall, scoliosis, precuts excavate, MVP, higher % of CFTR genes, no cellular immune defects
• MAC (mycobacterium avium complex): variable presentation, e.g. COPD, no previous lung disease, hot tub lung, HIV, Il-12 defects
• M. marinum: water, fish
• M. fortuitum: footbaths, nail salons, piercings

Question 3

Risk factors for TB in the US

Answer 3

• exposure history
• foreign born from areas of high TB prevalence
• HIV infection and other conditions assoc. with immunosuppression
• Fibrotic changes on CXR assoc. with prior TB
• homeless, IV drug users, prison, health care workers, lab ppl, elderly in nursing homes

Question 4

History and physical: TB

Answer 4

Classic symptoms
-cough, >2 weeks
-may have hemoptysis
-low grade fever
-anorexia and weight loss
-night sweats
PE findings
-vary
-fever and respiratory rales most common
-exam often unrevealing

Question 5

Active TB assessment

Answer 5

• CBC and chemistry panel
• 3 separate morning sputum: Acid fast stain
• can do bronchoscopy
• treat with standard TB treatment pending cultures
• suspected TB should be put in isolation room
• confirmatory AFB culture in special media, takes up to 4 weeks to grow
• obtain drug susceptibility testing to rule out drug resistance
• PCR/DNA test is faster

Question 6

Pathogenesis of TB

Answer 6

• inhalation of infected droplets
• reaches lower respiratory tract
• Type IV hypersensitivity reaction 6-8 weeks after initial infection
• intracellular replication
• mostly, initial infection is latent: no symptoms
• reactivation of latent TB can occur years after in small % of people

Question 7

Clinical manifestations of primary TB

Answer 7

• usually children, but any age
• usually lower and middle lungs, and heals with no clinical symptoms in 90% of cases
• fibrosis and calcification

Question 8

Manifestations of post primary Active TB infection (tb reactivation)

Answer 8

• Upper lobes and apical segment of lower lobes
• progression is variable
• early: small granulomatous broncho-pneumonia infiltration
• caseation can occur
• infected sputum can be aspirated to other segments of lung
• CXR (non HIV): posterior segments of upper lobes (apices) or super segments of lower lobes
• CXR (HIV): can be normal CXR or with infiltrates in any lobes and any location

Question 9

Progression of Active TB

Answer 9

• Chronic parenchymal lesions: upper lobe destruction, fibrosis, and overdistended emphysema
• Hemoptysis: erosion of blood vessels within the TB lesion
• The lesions can also erode into blood vessels, leading to hematogenous dissemination can occur to one or more sites: lungs, CNS, genitourinary, skeletal, lymph nodes, etc

Question 10

Latent TB infection assessment

Answer 10

• PPD and TST (mantoux test)
  1. PPD>5mm
• HIV+
• known contact with person with active TB
• fibrotic changes on CXR with prior TB
• organ transplants, immunosuppressed
  2. PPD>10mm
• high risk: silicosis, DM, chronic renal failure, etc
• recent immigrants, IV drug users, residents employees in crowded settings
• children over 4 yo
  3. PPD>15mm
• person with no risk factors for TB

Question 11

Treatment of latent TB

Answer 11

• daily Isoniazid (INH) for 9 months
• risk of side effects increases with age, >35. Most weigh risks when deciding to treat
• liver fxn test to monitor high risk individuals
• Directly observed therapy (DOT) for better compliance

Question 12

Rx for active TB

Answer 12

• 6 month treatment course. First 2 months with RIPE

- then INH and rifampin for 4 more months