Toxoplasma gondii is a widespread intracellular protozoan parasite with a definitive host stage in cats. Immunocompetent persons are usually asymptomatic, but immunocompromised persons (especially HIV-positive persons with <100 CD4 cells/mm3) are susceptible to reactivation of latent disease with considerable morbidity and mortality.
Patients with central nervous system (CNS) toxoplasmosis most often present with symptoms consistent with intracranial mass lesions (headache, focal neurologic deficits, nausea/emesis, and/or seizure) or, less likely, encephalitis (fever, confusion, altered mental status). Contrasted computed tomography (CT) of the head typically reveals ring-enhancing lesions with a predilection for the basal ganglia. Magnetic resonance imaging (MRI) of the head is more sensitive than CT for identifying these lesions. Serologic tests for T gondii antibodies (IgG) are usually positive. Other causes of mass lesions in the brain in HIV-infected individuals include CNS lymphoma, cryptococcoma, tuberculoma, and brain abscess.
Ocular toxoplasmosis is a less frequent complication of HIV disease. Patients typically present with eye pain and decreased visual acuity. Retinitis may be diagnosed by ophthalmoscopic evaluation revealing characteristic exudates and hemorrhage. Toxoplasmosis retinitis appears as raised yellow-white, cottony lesions in a nonvascular distribution, unlike the edematous perivascular exudates of CMV retinitis.
Management and Disposition
There are two combination regimens considered to be first choice for the treatment of toxoplasmosis. The most commonly used regimen is pyrimethamine and sulfadiazine for 6 weeks or until neurologic findings have resolved; however, for those with sulfa allergies, pyrimethamine plus clindamycin is an alternative. If the patient presents with seizures, loading doses of antiepileptics such as fosphenytoin or levatiracetam should be administered along with benzodiazepines. All patients with acute symptomatic CNS toxoplasmosis infection should be admitted for treatment.
HIV-infected patients presenting with focal neurologic findings or seizures should be evaluated for meningitis and space-occupying lesions in the brain. AIDS-specific differential diagnoses include toxoplasmic encephalitis, CNS lymphoma, tuberculosis, and cryptococcal disease.
All HIV-infected patients should have a CNS space–occupying lesion excluded by imaging prior to lumbar puncture (LP).
Initial evaluation of the HIV-infected patient with possible CNS lesions should include CT or MRI imaging, LP, and triage management for bacterial meningitis. Further workup will require admission and infectious diseases consultation.
Toxoplasma gondii Infection. Contrast head CT showing typical multiple ring-enhancing lesions seen in T gondii CNS infection. (Photo contributor: Edward C. Oldfield III, MD.)
Toxoplasmosis Retinitis. Ocular toxoplasmosis is a common complication of HIV disease. The lesion is a focal destructive chorioretinitis that leaves well-defined, heavily pigmented scars, especially in the macular area. (Photo contributor: Department of Ophthalmology, Naval Medical Center, San Diego, CA.)