Infectious Disease · Opportunistic Infections
The facts most likely to be tested
Toxoplasmosis in HIV/AIDS patients typically presents as ring-enhancing lesions on CT or MRI of the brain when the CD4 count is <100 cells/mm³.
The classic triad of congenital toxoplasmosis consists of chorioretinitis, hydrocephalus, and intracranial calcifications.
Transmission of *Toxoplasma gondii* occurs primarily through the ingestion of oocysts from cat feces or undercooked meat containing tissue cysts.
The first-line treatment for active toxoplasmic encephalitis is a combination of sulfadiazine and pyrimethamine supplemented with leucovorin to prevent bone marrow suppression.
Primary prophylaxis for toxoplasmosis in HIV-positive patients with a CD4 count <100 cells/mm³ and positive Toxoplasma IgG is trimethoprim-sulfamethoxazole.
Patients with ocular toxoplasmosis typically present with unilateral vision loss and a focal necrotizing retinitis often described as a headlight in the fog appearance on fundoscopy.
Diagnosis of toxoplasmosis in immunocompromised patients is primarily based on clinical presentation and serology, with empiric treatment initiated before considering a brain biopsy.
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A 34-year-old male with a history of untreated HIV presents with a two-week history of progressive headache, confusion, and left-sided hemiparesis. His most recent CD4 count was 45 cells/mm³. A brain MRI reveals multiple ring-enhancing lesions with surrounding edema in the basal ganglia. He has no history of recent travel or sick contacts.
What is the most appropriate next step in management?
Initiate empiric therapy with pyrimethamine, sulfadiazine, and leucovorin.
The patient's presentation of ring-enhancing lesions in the setting of advanced HIV (CD4 <100) is classic for toxoplasmic encephalitis, necessitating immediate empiric treatment rather than invasive biopsy.
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Etiology / Epidemiology
Caused by Toxoplasma gondii; primary risk is undercooked meat or cat feces in immunocompromised patients.
Clinical Manifestations
Triad of ring-enhancing lesions on CT/MRI in HIV patients with CD4 < 100.
Diagnosis
Toxoplasma IgG serology for exposure; Brain biopsy is the definitive gold standard.
Treatment
Pyrimethamine plus Sulfadiazine plus Leucovorin; bone marrow suppression.
Prognosis
High mortality if untreated; prophylaxis required when CD4 < 100.
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Epidemiology & Etiology
Transmission occurs via ingestion of oocysts from cat litter or tissue cysts in undercooked pork/lamb. Most immunocompetent individuals are asymptomatic. Reactivation is the primary concern in patients with advanced HIV/AIDS.
Pertinent Anatomy
The parasite has a predilection for the central nervous system, specifically the basal ganglia. Ocular involvement manifests as chorioretinitis, affecting the retina and choroid.
Pathophysiology
Primary infection leads to latent tissue cysts. In the setting of severe immunosuppression, these cysts rupture, causing focal necrosis and inflammation. This results in the characteristic space-occupying lesions seen on neuroimaging.
Clinical Manifestations
Patients present with focal neurologic deficits, seizures, and altered mental status. Imaging reveals multiple ring-enhancing lesions with surrounding edema. Red flags include rapid neurologic decline and signs of increased intracranial pressure.
Diagnosis
Diagnosis is typically presumptive based on clinical presentation and positive Toxoplasma IgG. Brain biopsy remains the definitive gold standard if lesions fail to respond to empiric therapy. MRI is superior to CT for visualizing multiple lesions.
Treatment
The standard regimen is Pyrimethamine plus Sulfadiazine plus Leucovorin (to prevent myelosuppression). If allergic to sulfa, use Clindamycin. Contraindicated in pregnancy (use Spiramycin). Prophylaxis is indicated with TMP-SMX when CD4 < 100.
Prognosis
Prognosis is excellent with early treatment but poor if diagnosis is delayed. Key complications include permanent neurologic deficits and blindness from chorioretinitis. Patients require serial imaging to monitor for treatment response.
Differential Diagnosis
Primary CNS Lymphoma: usually solitary lesion, EBV positive in CSF
CNS Tuberculosis: usually basal meningitis, not ring-enhancing
Cryptococcosis: usually presents as meningitis, not focal mass
Neurocysticercosis: calcified cysts, history of travel to endemic areas
Progressive Multifocal Leukoencephalopathy: non-enhancing white matter lesions