The Unyielding Ring

A 38-year-old man from rural Cochabamba department, Bolivia presents to the emergency department with two weeks of progressive headache, confusion, and right arm weakness. He grew up in a mud-walled adobe house where triatomine insects were commonly observed during childhood. He immigrated to California six years ago. HIV was diagnosed incidentally three months ago; he has not yet started antiretroviral therapy. His CD4 count is 78 cells/μL and HIV viral load is 482,000 copies/mL.

On examination, temperature is 38.2°C, heart rate 98/min, blood pressure 124/78 mmHg. He is oriented to person only. There is a right arm drift and dysmetria on finger-nose testing; no meningismus is present. MRI brain with gadolinium reveals two ring-enhancing cortical and subcortical lesions in the left frontal and parietal regions with surrounding vasogenic edema. Toxoplasma gondii IgG is negative; serum cryptococcal antigen is negative; CMV PCR and EBV PCR are both undetectable.

Given the imaging findings and degree of immunosuppression, empiric therapy with pyrimethamine (200 mg loading dose, then 75 mg/day), sulfadiazine (4 g/day in divided doses), and leucovorin (10 mg/day) is initiated alongside dexamethasone. After 14 days, he shows no clinical improvement and repeat MRI demonstrates stable-to-mildly progressive lesion enhancement.

Lumbar puncture is performed. Opening pressure is 18 cm H₂O. CSF analysis shows 14 nucleated cells (predominantly lymphocytes), protein 82 mg/dL, and glucose 54 mg/dL (serum glucose 98 mg/dL). On wet mount examination of the CSF, the finding shown below is identified.