PET/CT imaging revealed that pulmonary tuberculosis (TB) lesions can stay in the lungs a long time after the patient is treated with antibiotics, according to a new study published in Nature Medicine.

After patients with TB are treated with several medications over the course of six months, there is no reliable way to determine when the antibiotics have successfully cured them. Tissue sample tests can return negative results for TB even when the microbe causing it remains in the lungs.

Researchers from the National Institute of Allergy and Infectious Diseases (NIAID) had 99 patients with pulmonary TB in South Africa undergo PET/CT exams before, during, and after standard treatment.
After the six months of treatment, the PET/CT scans showed that 76 of the 99 patients had lung lesions similar to those seen in untreated pulmonary TB patients. A year after that treatment was completed, 50 patients still had “radiological abnormalities.”

Most of the lesions did decrease in severity and size, but only 16 patients with those abnormalities did not have any TB lesions. The other 34 patients still had a significant amount of remaining lesions.

The findings also found that TB genetic material was present in the saliva and mucus sample of a large amount of patients who were considered to be cure of clinical symptoms after treatment was completed.

PET/CT was chosen because it’s able to measure the level of inflammation or lesions in the affected parts of the lungs. In a 2014 study, NIAID researchers found that PET/CT can predict the effectiveness of TB drug regimens.

The researchers aren’t sure how this might contribute to the risk of disease relapse, but the findings do suggest that there is a need for new diagnostic methods to determine if TB is present after treatment as well as better strategies for treatment.

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