A 50-year-old man presents to the emergency department with low back pain for 3 months. He is a known case of HIV and had a lung infection several years back. There is cachexia. The back is tender to palpation over the lumbar spine, range of motion is decreased, and paraspinal paresthesias are present. An x-ray of the spine shows an abscess at L4, with L5 demineralization and osteolytic lesions. An x-ray of the chest is shown. What is the diagnosis?