Cervical Lymphadenitis With a Failed IGRA Control
A 3-year-old boy, born in the United States and never vaccinated with BCG, presents with a 5-week history of a 2.5-cm firm, nontender right cervical lymph node. He has no fever, weight loss, or cough. Chest radiograph is normal. His grandmother, who lives in the home, completed treatment for smear-positive pulmonary tuberculosis 8 months ago. The boy's tuberculin skin test is 12 mm, and an interferon-gamma release assay is indeterminate because the mitogen control failed. Excisional biopsy shows necrotizing granulomas; acid-fast bacilli stain is negative and mycobacterial culture is pending. The family asks whether the node can simply be observed.
1. How should the tuberculin skin test and the indeterminate IGRA be interpreted, and what is the leading diagnosis? Address why a negative AFB smear does not settle the question.
Read the worked answer
The TST is positive at 12 mm, and in a child with a household TB contact and no BCG vaccination that is substantive evidence of M. tuberculosis infection. The IGRA is not negative: an indeterminate result caused by mitogen failure means the assay did not demonstrate T-cell responsiveness and cannot be used to exclude infection. A negative AFB smear is expected in paucibacillary lymph node TB and does not lower the pretest probability.
The leading diagnosis is tuberculous cervical lymphadenitis. Nontuberculous mycobacterial lymphadenitis is the main alternative, especially with a unilateral, nontender node and a normal chest radiograph, but the high-risk household exposure and a 12-mm TST favor TB. Culture remains the discriminator; tissue PCR can shorten the wait, but a negative molecular test does not rule out TB.
2. The family prefers observation to avoid another procedure and medicine. Compare observation, further excision, and empiric antituberculosis therapy, and state your recommendation.
Read the worked answer
Observation alone is not appropriate for presumed TB lymphadenitis in a young child: untreated node TB can progress and reflects disseminated infection risk. Excision is diagnostic but not curative; rely on it only if the diagnosis remains unclear after cultures and molecular testing. Empiric standard four-drug antituberculosis therapy (isoniazid, rifampin, pyrazinamide, ethambutol) should begin now because of the positive TST, compatible histology, and household exposure, with adjustment when susceptibility results return.
For lymph node TB, 6 months of therapy is generally sufficient if the organism is fully susceptible and the response is good. If cultures grow M. avium complex, stop antituberculosis drugs and reassess: many NTM nodes are managed by complete excision, with drugs reserved for incomplete resection, immunocompromise, or severe disease. The key is not to let the pending culture delay treatment of probable TB.
3. What should happen while culture is pending: isolation, reporting, and follow-up? Include how you would respond if culture grows Mycobacterium avium complex.
Read the worked answer
While cultures are pending, report the case to the local health department as suspected TB and ensure the household contact investigation is complete; the grandmother's prior treatment and the child's exposure should be reviewed. The child does not need airborne isolation if there is no pulmonary disease and the chest radiograph is normal, but use standard precautions and cover draining nodes. If culture grows M. tuberculosis, continue public health follow-up, verify susceptibility, and arrange directly observed therapy if adherence is a concern.
If it grows M. avium complex, no respiratory isolation or public health contact investigation is needed; inform the family, stop TB drugs, and complete excision or observe according to symptoms. Follow node size and systemic symptoms; repeat imaging only for new findings.