A 42-year-old male with a history of pneumocystis jiroveci pneumonia is found to have multiple ring-enhancing lesions on brain CT. Which of the following is most likely responsible for this patient’s abnormal scan?
1.Neoplasm
2.Bacteria
3.Virus
4.Prion
5.Protozoa
exp:
This patient is most likely HIV-positive, given his history of pneumocystis jiroveci pneumonia (PJP) infection and now ring-enhancing lesions on brain CT. The most commonly tested etiology of multiple ring-enhancing lesions on a brain CT of an HIV-positive patient is brain abscesses due to the protozoan Toxoplasma gondii.
You must also be aware that primary CNS lymphoma is very high on the differential in these cases, if not the most commonly observed pathology in HIV-positive patients. The distinction can often be made because lymphoma is usually a solitary lesion with uniform enhancement whereas Toxoplasma causes multifocal lesions that are ring enhancing. These distinctions are not absolute but can help in differentiation in these cases.
Toxoplasma causes brain abscesses in HIV patients that present with seizures, headache, and ring-enhancing lesions on CT. Toxoplasma is a protist that causes congenital toxoplasmosis in neonates born to infected mothers, and is one of the “ToRCHeS” infections. Neonates with congenital toxoplasmosis present with a classic triad of chorioretinitis, hydrocephalus, and intracranial calcifications. Cats are the host for Toxoplasma, and infection results from contact with cat feces or from ingested cysts in meat (most commonly pork). Pregnant women should avoid cats or cleaning litter boxes for this reason. Treatment is with sulfadiazine and pyrimethamine.
Illustration B depicts an MRI showing two ring-enhancing lesions typical of toxoplasmosis.