Tuberculosis in children — branching viva

Viva \u2014 Branching structured oral

Stem. A four-year-old boy is brought in thin, with a cough and intermittent fever for six weeks. His uncle was diagnosed with smear-positive pulmonary tuberculosis two weeks ago, and his chest radiograph shows right paratracheal lymph-node enlargement. [1]

Branch 1 \u2014 Classification on the spectrum

Examiner: Where does this child sit on the TB spectrum, and why does that matter? [1]

Model answer. He has TB disease, not exposure or TB infection alone, because he has both symptoms (six weeks of cough and fever with thinness) and a compatible radiograph (paratracheal lymph-node enlargement). The spectrum \u2014 exposure, TB infection (the child is well but infected), TB disease (symptoms and/or radiological signs) \u2014 matters because it dictates everything that follows: observe, treat infection, or treat disease. I classify his disease as intrathoracic, and by severity as non-severe (lymph-node, non-cavitary, smear-negative pattern). [1] [2]

Examiner follow-up: His uncle is the source case. Why is the contact the most useful piece of information here? [1]

Model answer. The contact history is often the most specific bedside finding in childhood TB, because it establishes recent exposure to a known infectious adult and lifts the pre-test probability of disease substantially. It also lets me obtain the source case's drug-susceptibility result, which may decide the child's empiric regimen if there is resistance, and it tells me where to direct contact tracing and source-case treatment to break the transmission chain. [1]

Branch 2 \u2014 Pathophysiology of rapid progression

Examiner: Why do young children progress so quickly to severe disease? Walk me through the mechanism. [2]

Model answer. Inhaled droplet nuclei reach the terminal airway, are taken up by alveolar macrophages, and form the primary (Ghon) focus; bacilli then drain to the regional node, and the focus plus node form the primary complex. Outcome hinges on cell-mediated containment. Young children, especially under five, have immature cell-mediated immunity and fail to contain the bacilli, so the same inoculum that produces silent infection in an older child drives rapid progression to intrathoracic disease, miliary or disseminated TB and tuberculous meningitis within weeks. This is why an exposed under-five contact receives presumptive preventive therapy even before infection is confirmed. [2] [1]

Branch 3 \u2014 Investigation strategy

Examiner: How do you confirm the diagnosis? [5]

Model answer. I confirm microbiologically where possible: two to three early-morning gastric aspirates (or induced sputum or stool) for Xpert MTB/RIF Ultra plus culture and phenotypic susceptibility. Xpert detects mycobacterial DNA and rifampicin resistance within hours and is more sensitive than smear in children, but a negative result does not exclude disease because childhood TB is paucibacillary. I read the chest radiograph for the lymph-node pattern, take a TST or IGRA to support infection, and test for HIV. I treat empirically on a compatible clinical and radiological picture even if the samples are negative. [5] [1]

Examiner probe: A TST and IGRA both come back. How do you use them? [8]

Model answer. TST and IGRA indicate TB infection, not disease. They support a disease diagnosis and screen contacts, but neither can rule TB in or out alone, and I interpret them alongside the clinical and radiological picture rather than in isolation. IGRA does not cross-react with BCG and needs a single visit, which suits older children; TST remains useful especially in young children. They must not delay treatment of compatible disease. [8]

Branch 4 \u2014 Treatment by classification and the TBM override

Examiner: What treatment do you give this boy, and how do you decide? [7]

Model answer. I decide by classification. His disease is non-severe (lymph-node, non-cavitary, smear-negative pattern), so I treat with the weight-based 4-month regimen \u2014 intensive phase then continuation \u2014 validated by the SHINE trial for minimal, lymph-node or non-cavitary disease, using child-friendly fixed-dose combinations and re-weighing at every visit to avoid under-dosing. If he had severe, cavitary, miliary or CNS disease, or was an infant, malnourished or HIV-positive, I would use the full 6-month regimen. For TB infection in a high-risk contact I give tuberculosis preventive treatment. [7]

Examiner probe: Six months later his younger sibling presents febrile, irritable and drowsy. What now? [6]

Model answer. I presume tuberculous meningitis until proven otherwise. I assess airway, breathing, circulation and conscious level, arrange urgent brain imaging (basal exudate, hydrocephalus, infarct), perform a lumbar puncture with CSF for cell count, protein, glucose, acid-fast bacilli, Xpert and culture, and start an extended intensive anti-TB regimen with corticosteroids empirically without waiting for confirmation. Outcome depends on treating in the prodrome rather than in coma, so I treat on suspicion. I manage raised intracranial pressure with neurosurgical input for hydrocephalus. [6]

Branch 5 \u2014 Public health: notification, contact tracing, source-case finding

Examiner: What are your public-health responsibilities in this family? [1]

Model answer. TB is a notifiable disease, so I notify the public-health unit and trigger contact screening of household and close contacts \u2014 symptom review, TST/IGRA, and chest radiograph where indicated. I give tuberculosis preventive treatment to under-five and immunocompromised contacts, because their risk of rapid progression outweighs the small cost of treatment. Critically, I find and treat the infectious source adult \u2014 children are usually infected by an undiagnosed adult in the household and are poor transmitters themselves \u2014 so closing the transmission loop is how I protect the next child. I support adherence, re-weigh and follow up to cure, and use a trained interpreter for the family. [1] [7]