CNS INFECTIONS-TOXOPLASMOSIS

SUMMARY

QUESTION
1. PRESENTATION: Toxoplasmosis: immunosuppressed patients (HIV, pregnancy) with undiagnosed lymphadenopathy or any granulomatous uveitis or retinitis.
2. Symptomatic acquired toxoplasmosis resembles infectious mononucleosis, and is usually self-limiting.
3. Congenital eye infection presents with posterior uveitis and may cause cataract.
4. EPIDEMIOLOGY: most infections are asymptomatic: in the UK >50% are infected by 70yrs.
5. COMPLICATIONS: In the immunocompromised (e.g. AIDS): myocarditis, encephalitis, brain lesions, stroke or seizures.

ANSWER
1. AIDS-related brain lesions: If you see multiple ring-enhancing lesions, think toxoplasmosis. (CNS lymphoma, TB, and bacterial infections are less likely)
2. Toxoplasma IgM: acute infection is confirmed by a 4-fold rise in antibody titre over 4wks or specific IgM (unreliable if HIV +ve).
3. Toxoplasma IgG: because toxo is a reactivation infection, patients typically have IgG (but not IgM) antibody to T gondii.
4. CNS Biopsy: do a brain biopsy if there is no improvement after empiric treatment, if there is a mass effect, or if there is only 1 lesion.
5. Some empirically treat single lesions if the CD4 count is < 100 and the patient hasn't been on toxo prophylaxis. Relapses occur often.

Reference(s)

Wilkinson, I., Furmedge, D. and Sinharay, R. (2017). Oxford handbook of clinical medicine. Oxford: Oxford University Press. Get it on Amazon.
Feather, A., Randall, D. and Waterhouse, M. (2020). Kumar And Clark’s Clinical Medicine. 10th ed. S.L.: Elsevier Health Sciences. Get it on Amazon.
Hannaman, R. A., Bullock, L., Hatchell, C. A., & Yoffe, M. (2016). Internal medicine review core curriculum, 2017-2018. CO Springs, CO: MedStudy.
Therapeutic Guidelines. Melbourne: Therapeutic Guidelines Limited. https://www.tg.org.au [Accessed 2021].