Lung cancer and pulmonary sarcoidosis were also excluded both clinically and biologically; paratracheal lymph node biopsy revealed the presence of lymph node necroinflammation and histiocyte infiltrates, with no associated malignant cells, which excluded lung cancer, and serum levels of angiotensin-converting enzyme (ACE) (an important serum marker in the diagnosis of sarcoidosis) were in the normal range, which suggested the absence of pulmonary sarcoidosis, which ultimately raised the suspicion of an obscure post-infectious inflammatory syndrome. This evidence concerns the gene ACE and pulmonary sarcoidosis.