Hypermetabolic pulmonary lesions on FDG-PET/CT: Tularemia or neoplasia?

Objectives: Pulmonary tularemia is a rare and little-known disease, whose clinical and radiological presentation can be confused with those of much more frequent pathologies, such as lung cancer or B-cell lymphoma (46,000 and 5,000 new cases respectively per year in France). Furthermore, PET/CT is a powerful tool for the diagnosis of malignancies or the exploration of fever of unknown origin. The objective of this study was to describe the characteristics of pulmonary tularemia and to determine whether its PET/CT aspect could help distinguish it from neoplasia.

Methods: Retrospective observational study collecting all pulmonary tularemia cases for which a PET/CT was performed between 2016 and 2020.

Results: Twenty-seven cases of pulmonary tularemia were analyzed. The sex ratio was 4.4, and the median age was 60 years. Clinical manifestations were mainly represented by fever (n=23), arthralgia (n=7) and cough (n=6). PET/CT revealed intensely hypermetabolic mediastinal adenopathies in all cases, associated with parenchymal (n=20) or pleural (n=6) lesions, suggesting neoplastic pathology in 15 patients. Cytopuncture or lymph node biopsy was performed in 16 patients, revealing non-specific adenitis (n=8), necrotic epithelio-gigantocellular granuloma (n=3), or were non-contributory (n=5). All patients reported significant environmental exposure. The outcome was favorable for all patients, spontaneously for 8 of them and after antibiotic therapy with either doxycycline or ciprofloxacin for the other 19.

Conclusions: Depending on the epidemiological setting, pulmonary tularemia may be considered an alternative diagnosis to lung cancer, lymphoma, or tuberculosis, in the presence of infectious symptoms and hypermetabolic pulmonary lesions and mediastinal lymphadenopathies on PET/CT.