Toxoplasma encephalitis in an immunocompetent patient, a case report

Authors

Abstract

Toxoplasma encephalitis is an opportunistic infection primarily affecting immunocompromised individuals. Transmission typically occurs through the ingestion of undercooked meat, exposure to oocysts in cat feces, contaminated water, and less commonly, raw shellfish. The disease usually results from the reactivation of latent tissue cysts. While it is most commonly seen in patients with a CD4 count below 200 cells/mm³, the risk increases significantly when the count falls below 50 cells/mm³. The most frequent presentation is focal encephalitis, leading to seizures, hemiparesis, and aphasia. This case report presents a rare occurrence of toxoplasma encephalitis in an immunocompetent patient. A 68-year-old male with diabetes mellitus and congestive heart failure was admitted with right-sided weakness, speech difficulty, and numbness. Initial brain MRI suggested a lymphoma-like mass, but stereotactic biopsy confirmed toxoplasmosis. Despite the patient’s normal HIV status and high CD4 count, toxoplasma encephalitis was diagnosed. Treatment with pyrimethamine, clindamycin, and folinic acid led to significant clinical and radiological improvement. This case highlights that toxoplasma encephalitis should be considered in the differential diagnosis even in immunocompetent individuals presenting with focal neurological deficits and atypical MRI findings.
This case report aims to emphasize that toxoplasma encephalitis, although rare, can occur in immunocompetent individuals and should be considered in the differential diagnosis of patients with focal neurological deficits and atypical brain MRI findings.

Keywords

Introduction

Toxoplasma encephalitis is an opportunistic infection caused by Toxoplasma gondii. It is most commonly transmitted by ingestion of raw or undercooked meat containing tissue cysts, by oral ingestion of Oocysts are excreted in the feces of infected cats, by contaminated hands, water, and food, and less commonly by ingestion of raw shellfish. The disease almost always occurs by reactivation of latent tissue cysts. It is usually seen in patients with a CD4 count below 200 cells/mm³, but the risk is higher in patients with a CD4 count below 50 cells/mm³. The most common form is focal encephalitis, which presents with findings such as seizures, hemiparesis, and aphasia due to focal deficits ¹. In this study, a case of toxoplasma encephalitis detected in an immunocompetent patient, which is very rare in the literature, is presented. The informed consent form was obtained from the patient.

Case Presentation

A 68-year-old male patient diagnosed with diabetes mellitus and congestive heart failure was admitted to the neurology clinic with complaints of weakness, speech difficulty, and numbness in the right hand and right leg for approximately 5 months, and a space-occupying lesion compatible with lymphoma was detected in the brain MRI. A stereotactic biopsy performed two months later for differential diagnosis revealed toxoplasmosis in the mass. The patient was admitted to the infectious diseases ward with a diagnosis of toxoplasma encephalitis. Serological examination revealed toxoplasma IgM: (-), IgG: (+), and IgG avidity: 24.7 (high avidity). HIV was investigated for possible immunosuppressive etiology and anti-HIV: (-), HIV RNA (-), CD4: 960 cells/mm³ were found. There was no growth in blood cultures and other laboratory tests were normal. The patient was started on pyrimethamine, clindamycin, and folinic acid treatment with the diagnosis of toxoplasma encephalitis. Except for clindamycin, all were supplied from abroad. During the waiting period for the drugs, trimethoprim/sulfamethoxazole 20 mg/kg/day treatment was given for
14 days, when the drugs arrived, pyrimethamine 200 mg loading dose for 16 days, then 75 mg/day maintenance, folinic acid 25 mg/day, and clindamycin 300 mg 4*1/day were given. The patient developed a significant tremor during follow-up, and this was attributed to secondary parkinsonism in the neurological evaluation, and levodopa treatment was initiated. After a total of 30 days of treatment, a control brain MRI revealed focal signal changes consistent with gliosis in the supratentorial area, dramatic shrinkage in the mass, and no abscess formation. The patient was discharged after a total of 45 days of treatment and clinical improvement. A control MRI performed two months later reported gliosis in the supratentorial area, and no abscess formation was observed. A control MRI performed 3 months after the last MRI revealed a completely normal radiological appearance, except for the sequelae of gliosis.

Discussion

T. gondii is an obligate intracellular protozoal parasite. T. gondii has three forms: tachyzoite (a rapidly multiplying form), bradyzoite (a slower-growing form found in tissue cysts), and sporozoite (found in oocysts) ². The parasite is acquired orally, transplacentally, or, rarely parenterally in laboratory accidents by transfusion or from a transplanted organ. Exposure to kittens, eating uncooked or raw meat, mussels, oysters, or vegetables contaminated with cat feces, drinking unpasteurized goat milk, or drinking untreated water has been associated with an increased risk of toxoplasmosis ^3,4.
Common symptoms of cerebral toxoplasmosis are headache, usually accompanied by fever, and altered mental status. Patients may also present with visual disturbances, seizures, cranial nerve abnormalities, and sensory deficits. Focal neurological symptoms are common and include motor weakness and speech disorders ⁵. In our case, the
patient had no fever, headache, or altered mental status. Toxoplasmic encephalitis presented with focal neurological symptoms such as right hemiplegia and speech disorder.
Lesions are usually multiple, but in some series, about half of the patients had a solitary lesion. Since the spread to the brain is hematogenous, the distribution is close to the corticomedullary junction within the thalamus and basal ganglia, where the small terminal arteries are embolized (6). In our case, there was a single solitary lesion measuring 32 × 15 mm with contrast enhancement extending to the right high frontal, corpus callosum, and adjacent ependymal surface.
On MRI, toxoplasmosis lesions typically show high signals on long T2-weighted images representing the necrotic component of the abscess and perifocal edema. The hallmark imaging feature of toxoplasmosis is the asymmetric target sign. Toxoplasmosis lesions usually appear homogeneously nodular or ring-shaped ⁷. In our case, the asymmetric target sign, which is distinctive for toxoplasmosis, was absent, and a lesion with an atypical appearance for toxoplasmosis was present.
In the differential diagnosis of ring-shaped lesions in the white matter, we should also consider these diseases; multiple sclerosis, brain abscess (bacterial, mycobacterial, cytomegalovirus), central nervous system lymphoma, deep white matter ischemia, acute disseminated myeloencephalitis, progressive multifocal leukoencephalopathy, posterior reversible encephalopathy syndrome ⁸. In our case, the lesion in the patient’s brain MRI was consistent with central nervous system lymphoma, but no unusual findings were detected in the patient’s hematological examinations. A biopsy was taken from the lesion for the diagnosis of brain abscess and lymphoma, and microbiological and pathological examinations were performed. Lymphoma was not detected in the lesion and toxoplasma bradyzoites
were seen as a result of microbiological examinations.
The most commonly used regimen in the treatment of toxoplasma encephalitis is the combination of pyrimethamine 50-100 mg/day with or without folic acid and sulfadiazine 4-8 g/day. However, this regimen usually leads to unwanted side effects and relapses. The other most commonly preferred regimen is the use of clindamycin instead of sulfadiazine. Macrolide antibiotics, atovaquone, fluorouracil, trimethoprim/sulfamethoxazole, minocycline or doxycycline, dapsone, rifabutin, pentamidine, diclazuril, folinic acid, and trimetrexate are other agents used ⁶. In our case, we preferred to apply pyrimethamine+clindamycin combination treatment to avoid the side effects of sulfadiazine and the risk of relapse. With this treatment, the patient achieved a dramatic response in a short time. Focal neurological findings regressed, and radiological lesions completely disappeared. No side effects related to the drugs were observed in the patient during the treatment.

Conclusion

Although toxoplasma encephalitis is usually seen in immunocompromised individuals, it can also be seen in immunocompetent individuals, as in the case presented. In immunocompetent individuals presenting with non-specific findings such as fever, neurological deficits, and headache, toxoplasma encephalitis should be considered as a differential diagnosis. Radiological findings may not be specific. Biopsy samples taken from patients with symptoms such as neurological deficits, fever, and headache, and lesions detected on brain imaging, should definitely be evaluated for microbiological diagnosis.

Declarations

References

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Additional Information

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Conference Presentation
This study was presented as a poster at KLIMIK Congress, Antalya, Türkiye, 2019

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About This Article

Received:

December 23, 2024

Accepted:

January 23, 2025

Published Online:

March 28, 2025