Discussion
Pulmonary cryptococcosis presenting with multiple cystic lesions is a rare phenomenon. Moreover, in our patient, the lesions enlarged after the initiation of treatment although cryptococcosis was controlled. Our experience shows that pulmonary cryptococcosis might present with multiple cystic lesions during the course of treatment. Moreover, new clinical symptoms such as exertional dyspnea might be observed and careful follow-up is required after treatment.
Cryptococcosis occurs in both immunocompetent and immunocompromised individuals2. The radiographic features of pulmonary cryptococcosis are varied, depending on the immunological status of the host1. Patients with RA show immunodeficiency due to drug treatment and autoimmune inflammation, as well as variable CT findings and distribution in pulmonary cryptococcosis4,5.
In pulmonary cryptococcosis, cavitation is occasionally detected on CT, especially in immmunocompromised patients1. There have been few case reports of pulmonary cryptococcosis with multiple cystic lesions. A lung cyst is defined as any round circumscribed space surrounded by an epithelial or fibrous wall of variable thickness that usually measures less than 3 mm. It can be distinguished from a cavity in which the wall thickness is greater than 3 mm6. The radiographic findings in the present case presented as cysts. Takata et al. reported a case of secondary pulmonary cryptococcosis presenting with multiple cystic shadows in a patient with RA, with size reduction of cystic lesions after the initiation of treatment7. However, in our case, the cystic lesions became coalesced with each other, taking on a thin-walled state, and became enlarged, despite improvement in clinical manifestation and antigen titer. A previous report has indicated that the radiologic resolution of pulmonary cryptococcosis following antifungal therapy is usually gradual and incomplete3. Residual abnormalities, including bronchiectasis, cavitation, and/or fibrotic scars, are frequently observed, most notably on CT3.
We speculated that the mechanism of the formation and development of cysts in this case refer to the etiology of other diseases presenting with multiple cystic lesions. Pathologically, most nodules and masses seen on radiographic patterns in pulmonary cryptococcosis are characterized by granulomatous reactions. Langerhans cell histiocytosis (LCH) is characterized by the infiltration of Langerhans cells mainly in the lungs, leading to the activation of an inflammatory process with potential dysfunction in the affected sites8. Granuloma formation in LCH is similar to the distribution of pulmonary cryptococcosis9. The pathogenesis of pulmonary cysts in LCH is speculated to be peribronchiolar distribution of granulomatous inflammation and fibrosis, leading to a check-valve mechanism9. Regarding the pathogenesis of cystic changes in infectious lung disease such as Pneumocystisjirovecii pneumonia in HIV-infected patients and staphylococcal pneumonia, a check-valve mechanism and excavation of necrotic material via draining bronchi play an important role in forming cystic lesions10,11.
Therefore, cystic changes in the present case might have been caused by transbronchial discharge of necrotic material and granulomatous involvement and fibrosis of the bronchioles, leading to a check-valve mechanism.
In conclusion, multiple cystic lung lesions that enlarge after treatment are a rare manifestation of pulmonary cryptococcosis. Even if infection control of cryptococcosis is achieved after the initiation of treatment, clinicians should continue to observe the patients carefully.