Isolated pulmonary Cryptococcus neoformans infection presenting with severe pulmonary involvement: a case report

BACKGROUND: Pulmonary cryptococcosis is an uncommon fungal infection typically seen in immunocompromised hosts. In individuals with only mild immunosuppression, the disease is rare, often mimicking bacterial pneumonia, leading to diagnostic delays and inappropriate treatment. CASE PRESENTATION: We report a 50-year-old Chinese man with poorly controlled diabetes mellitus and myasthenia gravis on low-dose corticosteroids who presented with fever, cough, and hypoxemic respiratory failure. Initial imaging suggested severe community-acquired pneumonia, and broad-spectrum antibiotics were administered, but there was no clinical response. Chest CT revealed bilateral patchy consolidations, and bronchoalveolar lavage cultures confirmed Cryptococcus neoformans. Lumbar puncture excluded central nervous system involvement. The patient was initially treated with amphotericin B, but therapy was complicated by acute kidney injury, requiring a switch to flucytosine and fluconazole. Despite this, he demonstrated marked clinical and radiological improvement, with near-complete resolution at 6 months. CONCLUSION: Pulmonary cryptococcosis can masquerade as community-acquired pneumonia, delaying appropriate management. Clinicians should maintain a high index of suspicion in patients with prolonged corticosteroid use, poorly controlled diabetes mellitus, and poor response to antibiotics. Early recognition and timely antifungal therapy are vital to improving outcomes.