Positive, But Wrong

A 44-year-old man with acute myeloid leukemia presents on day 28 following allogeneic hematopoietic stem cell transplantation with persistent fever despite five days of piperacillin-tazobactam and vancomycin. He underwent myeloablative conditioning with busulfan and fludarabine and received a matched unrelated donor graft. Tacrolimus and methotrexate are in use for graft-versus-host disease prophylaxis. He has remained profoundly neutropenic with an absolute neutrophil count of 80 cells/μL.

Over the past 48 hours he has developed multiple skin lesions: firm, erythematous papules 3 to 8 mm in diameter scattered across his trunk and proximal extremities, several with a central umbilication and pale necrotic center. He reports no pain at the sites. Two sets of blood cultures obtained at the onset of fever are still without growth at 72 hours. Serum (1→3)-β-D-glucan is 480 pg/mL (reference: less than 80 pg/mL). Serum cryptococcal antigen by lateral flow assay (IMMY CrAg LFA) returns positive at a titer of 1:8.

The team considers starting empiric liposomal amphotericin B for presumed cryptococcosis. On examination, the patient is febrile to 39.2°C, heart rate 104 bpm, and blood pressure 108/66 mmHg. He is alert and oriented. No meningismus is present. The skin lesions are as described, without fluctuance. There is no hepatosplenomegaly. CT of the chest, abdomen, and pelvis shows no pulmonary nodules and no hepatic or splenic lesions. Chest X-ray is unremarkable.