TB Flashcards
Natural history of TB - active vs latent
A proportion of patients clear the infection but the majority control the infection and develop latent TB
Of those with latent TB around 10% will develop active TB in their lifetime
Tuberculosis infection (TBI) [newer term for latent tuberculosis]
Asymptomatic, not infectious but carriers of the organism
Treatment for latent infection with drug-susceptible M. tuberculosis (4)
6 months of isoniazid
or
12 weekly doses of rifapentine and isoniazid
or
1 month of daily rifapentine and isoniazid
Relationship between TB and HIV
HIV increases risk of active TB and higher mortality
More likely to develop extrapulmonary manifestations, particularly with low CD4 counts: including thoracic lymphadenopathy and pleural effusion, lymphadenitis, TB meningitis
Regarding IRIS
Start ART within 2 weeks after TB Rx
Start ART 4-8 weeks post-Rx in TB meningitis
Drug susceptible TB treatment in adults
Traditional regimen (≥6 months):
Intensive phase: isoniazid, rifampin, ethambutol, and pyrazinamide administered for 2 months
Continuation phase: isoniazid and rifampin administered for at least 4 months
Shortened (4-month) regimen:
Intensive phase: rifapentine, isoniazid, pyrazinamide, and moxifloxacin administered for 8 weeks
Continuation phase: rifарentinе, iѕοniаzid, and moxifloxacin administered for 9 weeks
Diagnostics in TB (TST)
Test of immune reactivity for TB
Based on delayed-type hypersensitivity reaction to purified protein derivative (PPD)
After 48-72 hours, the injection site is examined for induration (positive >10mm or >5mm in children with HIV/malnutrition
Advantages: Inexpensive, easy to administer, no special equipment needed.
Limitations: Cannot differentiate between latent TB infection and active disease; cross-reactivity with BCG vaccine and other mycobacteria can lead to false positives.
Diagnostics in TB (IGRA)
Blood test measuring immune response (specifically, interferon-gamma production) to TB antigens.
Advantages: More specific than TST, unaffected by prior BCG vaccination, no need for return visit.
Limitations: Higher cost than TST, requires laboratory infrastructure, cannot distinguish between latent and active TB.
Diagnostics in TB (smear)
Sputum examined to detect acid fast bacilli (AFB)
Either auramine stain or Ziel-Nielson. LED fluorescence microscopy can be used to improve sensivity
Advantages: Widely used, rapid, inexpensive.
Limitations: Limited sensitivity (particularly in HIV-positive or extrapulmonary TB cases), cannot differentiate TB species, requires skilled technicians.
Diagnostics in TB (culture)
Sputum or other samples cultured in specialised media (e.g., Lowenstein-Jensen or liquid culture media) to grow Mycobacterium tuberculosis.
Advantages: Most sensitive so considered the gold standard for TB diagnosis; allows drug susceptibility testing.
Limitations: Time-consuming (weeks for results), requires specialised laboratory setup.
Diagnostics in TB (Molecular)
Molecular Tests
Types:
Xpert MTB/RIF: Detects TB DNA and resistance to rifampicin.
Line Probe Assays (LPAs): Detects specific genetic mutations linked to drug resistance.
Whole Genome Sequencing (WGS): Provides a complete genetic profile of TB, offering insight into resistance and transmission.
Advantages: Rapid (within hours), highly sensitive and specific, can detect drug resistance
Limitations: Expensive, requires advanced laboratory infrastructure, often limited to centralized labs, still not as sensitive as culture
Features of extrapulmonary TB
Lymphadenitis
GUM
Peritonitis
Meningitis
Pleurisy
Spinal
Intraocular
TB lymphadenitis
Most common form - cervical, mesenterial
Painless with mild inflammation
Without treatment can develop liquification
Diagnosis - large needle biopsy.
No surgical management required, may come and go until months after the therapy
TB pleurisy
Seen in primary TB 6-12 weeks and in reactivation
Usually unilateral, 10% bilateral
Exudate, very high protein >30, pH 7.3, leucocytes
Pleural biopsy for histopathology and micro is most sensitive
Usually don’t need drainage
TB spondylitis
50% of all bone TB
Pain sometimes with focal neurology
Complications include psoas abscess
Abdominal TB
Can involve any part of the gastrointestinal tract, as well as the peritoneum, mesenteric lymph nodes, and liver. Symptoms include abdominal pain, weight loss, and ascites
