Cerebral Toxoplasmosis in AIDS Patients : Clinical Manifestations and Laboratory Diagnosis

Abstract

Background : Patients with acquired immunodeficiency syndrome (AIDS) are susceptible to a variety of infections. Cerebral toxoplasmosis is one of the most common. The presumptive diagnosis is based on clinical manifestations, a positive Toxoplasma antibody test, characteristic neuroradiological abnormalities, and improvement after specific therapy. We evaluated not only the clinical manifestations and laboratory diagnosis but also its prevalence and the CD4 count in relationship to the development of cerebral toxoplasmosis in order to determine its place in the natural history of HIV infection.
Methods : A retrospective cohort study was performed in 104 AIDS patients who were stratified into three levels: 35 with a definite diagnosis of cerebral toxoplasmosis and 41 with a probable diagnosis and 104 with a possible diagnosis. The criterion for diagnosing definite illness was a good response to specific treatment. Toxoplasma IgM were detected using solid-phase enzyme immunoassay and monoclonal captured ELISA methods respectively in all patients. 65 cases without a definitive diagnosis were further investigated with a CT scan of the brain. The patient data were followed up on day 7 and 14.
Result : Toxoplasma IgG was present in 37 out of all case (35.6%) and Toxoplasma IgM was positive in only one case. The study showed that ELISA was a valuable method for diagnosis in addition of a CT scan of the brain. The ELISA detected antibodies in 24 out of 35 cases with a definite diagnosis (sensitivity 68.6%, 95% CI 5.7%-83.2%) and no antibody in 56 out of 69 cases with other diagnoses (specificty 81.2%, 95% CI 69.9%-89.6%). The CT scan showed positive features in 30 out of 33 cases with definite diagnosis (sensitivity 90.9%, 95% CI 75.7%-98.1%) but there were 4 (out of 32 cases) with a positive CT scan who were negative for the diagnosis, i.e., false positive, giving a specificity of 87.5%, 95% CI 71.0%-96.5%. The most common clinical presentations were headache and neurological deficit. Interestingly, neurological deficit was the only clinical manifestation that was associated with cerebral toxoplasmosis, when the group with a definite diagnosis was compared with the other diagnosis group (p-value 0.006). In HIV seropositive patients with previous Toxoplasma infection, cerebral toxoplasmosis was present in 24 out of 37 cases who were positive for Toxoplasma IgG (positive predictive value 64.9%), particularly in individuals with a CD4 count less than 100 cells/mm3.
Conclusion : The two most common clinical manifestations were headache and neurological deficit. Detection of Toxoplasma gondii IgG and CT scan of the brain are valuable tools for the diagnosis of cerebral toxoplasmosis. Cerebral toxoplasmosis is mainly caused by reactivation, as Toxoplasma IgM antibodies were found in only one case.