Contributions of Immunoblotting, Real-Time PCR, and the Goldmann-Witmer Coefficient to Diagnosis of Atypical Toxoplasmic Retinochoroiditis

Abstract

Ocular toxoplasmosis is a major cause of posterior uveitis worldwide. The diagnosis is based mainly on ophthalmological examination. Biological diagnosis is necessary in atypical cases, and this requires aqueous humor sampling by anterior chamber paracentesis. We evaluated real-time PCR targeting the Toxoplasma gondii 529-bp repeat element, the Goldmann-Witmer coefficient (GWC), and immunoblotting for the diagnosis of toxoplasmic retinochoroiditis in 54 patients with atypical uveitis. The results of these biological tests, applied to paired aqueous humor-serum samples, were compared to the clinical findings. Combining either PCR or the GWC with immunoblotting increased the sensitivity to 73% or 70%, respectively. Together, PCR and the GWC had 80% sensitivity. If feasible, sensitivity can be increased by combining the three methods (85% sensitivity). The interval between symptom onset and anterior chamber paracentesis strongly influenced the detection of specific intraocular antibody synthesis. The sensitivity of the GWC increased from 45% to 56% when sampling was performed 10 days after symptom onset, and that of immunoblotting increased from 53% to 72% when puncture was performed 30 days after symptom onset. PCR analysis of aqueous humor samples detected toxoplasmic DNA in 55% of patients. In contrast to the results of immunoblotting and the GWC, the results of PCR were not influenced by the interval between symptom onset and paracentesis. PCR was more informative than the GWC and immunoblotting for immunocompromised patients. Acute necrotizing retinal lesions were significantly larger in PCR-positive patients, with a mean of 3.5 optic disc diameters, than in PCR-negative patients, with a mean of 1.5 optic disc diameters.

Molecular Detection and Genotyping of Toxoplasma gondii from Clinical Samples

“…Lately, molecular methods are becoming a standard diagnostic approach in the diagnosis of ocular toxoplasmosis as well. A number of studies has already shown that a positive PCR result is not always accompanied by positive serology indicating local synthesis of IgG antibodies Talabani et al, 2009) and thus can be the only confirmation of the diagnosis (Okhravi et al, 2005).…”

An ophthalmologist survey-based study of the atypical presentations and current treatment practices of ocular toxoplasmosis in India

“…Viral retinitis and ocular tuberculosis, both of which can cause focal chorio-retinal lesions, were reported the most likely differential diagnoses for atypical OT. To accurately diagnose OT in such a situation, additional investigations would be needed (Fardeau et al 2002;Mahalakshmi et al 2006;Talabani et al 2009). These include detection of toxoplasma DNA in ocular fluids with polymerase chain reaction and intra-ocular antibody testing for the Goldman-Witmer co-efficient.…”

“…Hence, we suspect that a large pool of OT lesions would belong to the 'atypical' category. Such lesions may be confused with other infectious and non-infectious conditions and need additional tests for accurate diagnosis, unlike the typical lesions (Fardeau et al 2002;Mahalakshmi et al 2006;Talabani et al 2009). …”

A new era of uveitis: impact of polymerase chain reaction in intraocular inflammatory diseases

“…PCR for the detection of a Toxoplasma-specific gene region is reported to be useful [13,127]. In our previous study [13], PCR analysis using a combination of multiplex qualitative PCR and real-time quantitative PCR assays of intraocular fluids, mostly the aqueous humor, detected DNA of Toxoplasma gondii in all patients with active uveitis, but not in patients with inactive old lesions (Fig.…”

“…11). In addition, to prove that the antibody production against T. gondii is taking place in the eye, it is useful to calculate the GWC [127,128]. The sensitivity of diagnosing ocular toxoplasma can be further improved by Fig.…”