**5. Diagnosis**

There are no obvious or non-specific clinical manifestations of toxoplasmosis in competent hosts which are unique to the disease. Most of the time, infections are overlooked. Thus, it is not straightforward to diagnose. Serological testing in such patient is the main identifying evidence of specific antibody. In TE reactivation, clinical features are more helpful than serological testing in term of diagnostic criteria.

Centre for Disease Control and Prevention (CDC), the National Institutes of Health, and the HIV Medicine Association of the Infectious Diseases Society of America recommend that making a definitive diagnosis of TE requires 1) compatible clinical features; 2) single or multiple mass lesions by computerized tomography (CT), magnetic resonance imaging (MRI), or other radiographic testing; and 3) the most important is detection of the organism in a clinical sample. This requires a brain biopsy performed by a stereotactic CT-guided needle biopsy. Organisms are demonstrable with hematoxylin and eosin stains and immunohistochemistry staining by experienced laboratories might increase sensitivity (CDC 2009). However, these are always impracticable due to patients' conditions. For clinically suspected TE cases, CDC criteria should be applied for a presumptive diagnosis i.e. 1) the recent onset of a focal neurological abnormality that is consistent with intracranial disease or reduced consciousness; 2) evidence from brain imaging of a lesion with mass effect and ring enhanced appearance after injection of a contrast medium; and 3) positive serum antibody to *T. gondii* or successful response to anti-toxoplasmic treatment (Sukthana, 2006). By using these presumptive diagnostic criteria, the positive predictive value is achievable in approximately 80% (Cohn et al, 1989; Katlama, 1992; Luft et al, 1993).

On brain imaging, most of TE lesions occur in the basal ganglia, thalamus and corticomedullary junction (Lee et al, 2009). MRI is more sensitive than CT, Weenink and colleagues reported a TE patient who showed a normal contrast-enhanced CT scan, but MRI revealed clear abnormalities in the basal ganglia (Weenink et al, 2009). TE usually appears as multiple nodular or ring enhanced lesions with edema and mass effect. However, 14% of cases showing a solitary lesion which need to be differentiated from CNS lymphoma that more commonly presented as a single mass than toxoplasmosis (Legrand et al, 2010). Several techniques such as a diffusion weighted imaging; single-photon emission CT (SPECT) and positron-emission tomography (PET) could provide a more precise diagnosis (Sukthana, 2006; Legrand et al, 2010). Weighted MRI shows a peripheral hyperintensity of

Toxoplasmic Encephalitis 297

Treatment with PY+S has some limitations including 1) poor compliance due to side effects, particularly sulfadiazine; 2) the large number of pills needed; 3) unavailability in some countries; 4) high cost and 5) lack of an intravenous form. Nearly half of treated patients develop adverse effects such as gastrointestinal upset or rashes (Table 4) and require a change of therapy. Clindamycin is an alternative drug in the case of intolerance to sulfacompounds. A 600 mg every 6 hours for 3-6 weeks by oral or intravenous route is recommended (Mariuz & Steigbigel, 2001; Sukthana, 2006; Dedicoat & Livesley, 2008). The efficacy and adverse effects of the combination between pyrimethamine and clindamycin (PY+C) seem to be comparable with pyrimethamine and sulfadiazine (PY+S) combination (Table 5). However, when using PY+C as a maintenance regimen, the relapse rate was twice higher (P = .02) than those who received PY+S (Katlama et al, 1996). Diarrheoa was more frequent on PY+C, while skin rash and fever were more commonly encountered in the PY+S group. More drug discontinuation occurred in the PY+S than in PY+C group (11 vs. 30%, p=.001). Therefore, Katlama et al (1996) suggested that a combination of pyrimethamine and clindamycin is a good alternative for acute treatment but is less effective for long-term

**Drug Dosing/duration of treatment Adverse effects** 

Gastro-intestinal (GI) upset

Pseudomembranous colitis

Rash (including Stevens-Johnson

Rash

Cytopaenias

GI upset

syndrome) Cytopaenias Interstitial nephritis

Crystalluria Encephalopathy

GI upset Rash Diarrheoa

100 mg orally twice for 1 day, (loading dose) then 50-75 mg orally daily for 3-6 weeks

100 mg/kg (4-8 gm in four divided doses) orally daily for 3-6

600 mg every 6 hours for 3-6 weeks, orally or IV use

Table 4. Recommended dose, duration and adverse effects of the standard and alternative drug regimens for toxoplasmic encephalitis (Modified from Mariuz & Steigbigel, 2001).

Cotrimoxazole or trimethoprim-sulfamethoxazole (TMP-SMZ) is another regimen that has been studied and recommended as an alternative treatment in particular areas that pyrimethamine and sulfadiazine are not available especially in developing world (Torr et al, 1998; Béraud et al, 2009). Its efficacy was as high as 70-85.5%, while the mortality rate was low (Table 5). TE relapse occurrence was around one-third of the patients and successfully re-treated by TMP-SMZ. Rash and neutropaenia were the most common side effects which occurred in 12-13.8% of patients but only half required treatment discontinuation. With its low cost, availability in parenteral form with excellent diffusion into the CNS and wide availability in developing countries, TMP-SMZ thus could be the first-line drug regimen for

weeks

**Folinic acid** 10-20 mg orally daily for 3-6 weeks

prevention of the relapses.

**Pyrimethamine** 

**Sulfadiazine** 

**Clindamycin** 

**Or** 

TE mass lesion that is a feature helping to distinguish it from lymphoma. In comparison with TE and other infections, lymphoma displays high thallium uptake on SPET image. The rate of detection will be as high as 100% sensitivity and 89% specificity when the lesion is larger than 2 cm; otherwise it drops significantly if the lesion is smaller than 2 cm. PET imaging need more studies to determine its effectiveness (Lee et al, 2009). Among those techniques, none has high specificity and they are only useful when used in combination (Legrand et al, 2010). Moreover, they are costly and not widely available especially in resource-poor settings (Sukthana, 2006).

Routine laboratory tests of the cerebrospinal fluid (CSF) are not helpful for TE diagnosis because they are usually normal or non-specifically altered. Increased protein level could be seen in about 65% of patients, low glucose level in 8-52% and pleocytosis, predominantly mononuclear cells, in 27-40% (Collazos, 2003). Intrathecal level of *T. gondii* antibody is always low and of limited value for diagnosis because its sensitivity and specificity is about 60-70% (Collazos, 2003; Sukthana, 2006). Parasitic isolation from CSF is very rarely successful. Tachyzoites were seen in only 2 out of 6,090 examined ventricular CSF specimens and only 5 cases existed in the literature where a direct identification of *T. gondii* was possible by cytologic examination (Palm et al, 2008), however, those researchers reported a tachyzoites and bradyzoites of *T. gondii* directly seen in lumbar CSF cytology.

Most patients with TE have an evidence of past infection showing a low titre of *T. gondii* antibody, but it helps the diagnosis. The absence of the antibody thus argues against TE diagnosis (Collazos, 2003; Sukthana, 2006). Nevertheless, it is not impossible since 3-5% of patients with TE have negative serological finding (Collazos, 2003). DNA-amplificationbased techniques greatly contribute to the diagnostic improvement. Blood PCR as a single test is not sensitive. CSF PCR produced disappointing results with low sensitivity (50%), although specificity is high (96%-100%) and the results usually are negative once specific anti-toxoplasmic therapy has been started (Collazos, 2003; Sukthana, 2006; CDC, 2009). Repeated testing and combining both CSF and blood PCR enhance sensitivity. Tachyzoitebradyzoite stage-specific primers could provide a more precise diagnosis of reactivated toxoplasmic encephalitis, especially in recurrent cases (Contini et al, 2002; Cultrera et al, 2002; Mahittikorn et al, 2010). Sukthana used duplex reverse transcriptase PCR (RT-PCR) technique containing tachyzoite (SAG1) and bradyzoite (BAG1) specific genes developed by our colleagues (Mahittikorn et al, 2010) to diagnose Thai TE cases. It was found that RT-PCR technique is simple, easy to perform, and provides 85% positive predictive value when compared with CDC diagnostic criteria (to be published).
