27th June 2023

Cerebral toxoplasmosis

Toxoplasma gondii is a parasite spread through oocysts shed by infected cats. It is usually asymptomatic in people with a functioning immune system. Cerebral toxoplasmosis causes a multifocal necrotising encephalitis in people with HIV (usually CD4+ T-cell count is <200/μL), with subacute onset. Presenting features include:

• Subacute headache
• Focal neurological deficit
• Fever
• Confusion
• Seizures
• Ataxia

Radiology demonstrates ring-enhancing focal brain lesions. Contact is confirmed using an enzyme-linked immunosorbent assay (ELISA) which detects IgG and IgM antibodies against Toxoplasma gondii in the serum. This is sensitive but not specific, as many uninfected people have positive IgG titres for Toxoplasma gondii. Lumbar puncture (LP) can be used for PCR of Toxoplasma gondii DNA, however, this does not have a high sensitivity and patients with toxoplasma encephalitis may have mass effect, increasing the risk of brain herniation with an LP. Management of cerebral toxoplasmosis involves pyrimethamine and sulfadiazine with folinic acid. Second-line treatment and primary prophylaxis is with co-trimoxazole.