In a resident with a history of pulmonary tuberculosis who now has a 4‑day fever, lymphocytic leukopenia, and CT showing fibrocalcific nodules with new peribronchovascular nodules, what is the most likely diagnosis?

Reactivation Tuberculosis (Endobronchial Spread)

This clinical presentation is most consistent with reactivation tuberculosis with endobronchial spread of infection, and you should immediately initiate four-drug anti-TB therapy (INH, RIF, PZA, and EMB) while obtaining sputum specimens for AFB smear and culture. 1

Clinical Reasoning

Key Diagnostic Features Present

The CT findings are highly characteristic of active TB with endobronchial spread:

• New peribronchovascular nodules in the posterior segment of the right upper lobe and superior segment of the left lower lobe represent endobronchial spread of infection—a hallmark of active reactivation TB 1, 2
• Stable fibrocalcific nodules with cicatrization in the apical and posterior upper lobe segments indicate prior TB, which increases risk of reactivation 2.5-fold 1
• Fever for 4 days with lymphocytic predominance and leukopenia (WBC 3900) is consistent with active TB infection 1

Why This is Active TB, Not Just Old Disease

The CT report specifically notes "no significant interval change" in the old fibrocalcific nodules but describes new pulmonary nodules in peribronchovascular distribution. This pattern of new nodules superimposed on old scarring is pathognomonic for endobronchial spread from reactivated disease 1, 3, 4. The peribronchovascular distribution indicates lymphatic and airway spread of active infection 3.

Immediate Management Algorithm

Step 1: Initiate Treatment Immediately

Start four-drug therapy (INH, RIF, PZA, EMB) without waiting for culture results 1. The American Thoracic Society/CDC/IDSA guidelines explicitly state that patients with clinical and radiographic findings suggestive of pulmonary TB should have treatment initiated even when initial sputum smears are negative 1.

Step 2: Obtain Diagnostic Specimens

Collect at least three sputum specimens (using sputum induction with hypertonic saline if necessary) for AFB smears and mycobacterial cultures 1. If sputum cannot be obtained, consider bronchoscopy with bronchoalveolar lavage 1.

Step 3: Assess for Culture-Negative TB

Approximately 17% of pulmonary TB cases have negative cultures 1. If cultures remain negative but clinical suspicion remains high (as in this case with characteristic imaging):

• Continue treatment and reassess at 2 months 1
• If clinical or radiographic improvement occurs with no alternative diagnosis, continue treatment for culture-negative TB 1
• A 4-month regimen of INH and RIF is adequate for culture-negative TB (versus 6 months for culture-positive) 1

Critical Pitfalls to Avoid

Do not delay treatment waiting for culture results. Low bacillary populations, temporal variations in bacilli expelled, and processing errors can result in negative cultures despite active disease 1. The presence of new peribronchovascular nodules on CT in a patient with prior TB and fever is sufficient to initiate empiric therapy 1.

Do not assume the old fibrocalcific changes alone explain the fever. Inactive TB does not cause fever—the new nodules indicate active endobronchial spread 1, 2, 4.

Do not overlook drug resistance. Given the history of prior TB, obtain drug susceptibility testing once cultures are positive 1, 5. If the patient was previously treated, resistance patterns from prior treatment should guide current therapy 5.

Alternative Diagnoses to Consider (Lower Priority)

While the presentation strongly suggests TB reactivation, the differential for peribronchovascular nodules includes:

• Nontuberculous mycobacterial (NTM) infection: Less likely given the acute fever and classic upper lobe distribution, but culture will differentiate 1, 2
• Lymphoproliferative disease: The lymphocytic predominance could suggest lymphoma, but the peribronchovascular nodules with prior TB history makes this less likely 6, 7
• Sarcoidosis or vasculitis: Would not typically present with acute fever in someone with prior TB scarring 7

However, given the high pretest probability of TB reactivation with endobronchial spread, empiric anti-TB therapy should not be delayed while pursuing these alternatives 1.