Two cases of pulmonary cryptococcosis, negative of serum cryptococcal antigen and difficult to differentiate lung cancer

Background. Pulmonary cryptococcosis sometimes presents as a solitary pulmonary nodule, therefore problems in distinguishing lung cancer and cryptococcosis often arises. The usefulness of serum cryptococcal antigen for the diagnosis of pulmonary cryptococcosis has been emphasized. However there are not a few cases negative for serum antigen when pulmonary cryptococcosis appeared as a solitary lung nodule. Recently we encountered 2 cases of serum antigen-negative pulmonary cryptococcosis. Cases. Case 1 was found on a chest radiograph in an annual medical checkup and case 2 complained of low grade fever. Solitary pulmonary nodules were pointed out in both cases. Chest CT revealed spiculation of these nodules, but no daughter lesion. Therefore these nodules were strongly suspected to be lung cancer. Case 1 was diagnosed as cryptococcosis by fiber-optic bronchoscopy, case 2 was diagnosed by lung biopsy via thoracoscopy, and both cases were successfully treated by fluconazole. Conclusion. Serum cryptococcal antigen may not be detected in cases of pulmonary cryptococcosis presenting as a solitary lung nodule, therefore the development of more effective examinations is required.