Cerebral Schistosomiasis: Pathophysiology, Imaging, Diagnosis, and Treatment

Introduction

Cerebral schistosomiasis is a rare but clinically significant manifestation of Schistosoma infection, a parasitic disease that affects over 250 million people worldwide.

While schistosomiasis typically involves the urogenital or hepatointestinal systems, neurological involvement—known as neuroschistosomiasis—can result in severe complications, including seizures, focal neurological deficits, and cognitive impairment.

This article presents an in-depth analysis of cerebral schistosomiasis, drawing from a real case of a 33-year-old man who developed seizures and confusion after returning from São Tomé and Príncipe.

The discussion integrates the latest global literature on pathophysiology, epidemiology, clinical presentation, imaging features, differential diagnosis, treatment, and prognosis.

Case Presentation

A 33-year-old Caucasian male presented with severe headaches, focal seizures, and confusion three weeks after returning from São Tomé and Príncipe, where he had lived for five years.

His past medical history was unremarkable.

Two weeks before departure, he reported swimming in a local river against medical advice.

Days later, he developed a pruritic rash on his lower extremities, suggestive of cercarial dermatitis (“swimmer’s itch”).

On admission, physical examination was unremarkable, but neurological assessment revealed aggressive behavior without focal deficits.

Laboratory findings showed persistent eosinophilia without leukocytosis.

Serological tests were positive for anti-schistosomal antibodies, while stool and urine tests were negative for eggs.

Lumbar puncture revealed 28 mononuclear cells with normal protein and glucose levels. HIV and malaria were excluded.

Imaging Findings

Figure 1. Non-contrast Head CT and MRI

CT (a): Hypodense lesion with mild mass effect.
MRI FLAIR (b): Hyperintensity in cortical and subcortical regions.
T1 post-contrast (c, f): Patchy, irregular gadolinium enhancement.
DWI/ADC (d, e): No restricted diffusion.

Interpretation: Suggestive of an inflammatory lesion with a pseudotumoral appearance, raising suspicion for cerebral schistosomiasis.

Figure 2. MRI Progression During Treatment

(a) Baseline MRI: Lesion with significant mass effect.
(b) After 15 days: Enlargement with increased edema.
(c) After 3 months of therapy: Marked regression with only minimal residual lesions.

Interpretation: Favorable radiological response to praziquantel and corticosteroid therapy.

Pathophysiology

Cerebral schistosomiasis occurs when Schistosoma eggs or migrating adult worms lodge in the brain parenchyma or leptomeninges. The immune system mounts a granulomatous inflammatory response, leading to edema, gliosis, and pseudotumoral lesions.

Key species involved:
- S. japonicum – most common cause of cerebral involvement, particularly in Asia.
- S. mansoni and S. haematobium – typically affect the spinal cord but can involve the brain.
- S. intercalatum – endemic to São Tomé and Príncipe, rarely associated with CNS disease.

The pseudotumoral form is characterized by mass-like lesions with patchy enhancement, often misdiagnosed as neoplasms or demyelinating disease.

Epidemiology

Schistosomiasis affects 78 countries, with Africa bearing 85% of the global burden.
Cerebral schistosomiasis remains underreported due to diagnostic challenges.
Most cases are seen in endemic regions:
- S. japonicum → Asia (China, Philippines).
- S. mansoni → Africa, South America.
Cases in Europe and North America are almost exclusively among travelers or immigrants returning from endemic regions.

Clinical Presentation

Patients may present with:

Seizures (most common symptom).
Headache and intracranial hypertension.
Cognitive or behavioral changes (e.g., confusion, aggressiveness).
Focal neurological deficits (depending on lesion location).

In acute settings, symptoms may mimic viral encephalitis, stroke, or primary CNS tumors.

Imaging Features

MRI Characteristics of Cerebral Schistosomiasis:

T1-weighted: Hypointense lesions.
T2/FLAIR: Hyperintense signal with surrounding edema.
Post-contrast: Irregular, patchy, or nodular enhancement.
Diffusion: Typically no restricted diffusion (helps distinguish from abscess).

Differential Radiological Patterns:

Pseudotumoral form – space-occupying lesion, mass effect.
Nodular/linear enhancement – “branch-like” pattern considered characteristic.
Multiple small granulomas – “starry sky” appearance in some reports.

Differential Diagnosis

Primary CNS neoplasms (glioma, lymphoma).
Neurocysticercosis – cystic lesions with scolex, not seen here.
Cerebral malaria – endemic overlap, but imaging differs.
CNS vasculitis – excluded due to negative ANCA and ESR.
Autoimmune encephalitis – less likely given eosinophilia and epidemiological context.

Diagnosis

The diagnosis of cerebral schistosomiasis is based on:

Clinical history: Recent exposure to freshwater in endemic areas.
Laboratory findings: Eosinophilia, positive serology.
Neuroimaging: Pseudotumoral lesions with patchy enhancement.
Exclusion of alternatives: Negative malaria, HIV, and tumor markers.

Histological confirmation via brain biopsy is rare due to invasiveness.

Treatment

Antiparasitic therapy:
- Praziquantel – 40 mg/kg/day in two divided doses for 3 days.
Anti-inflammatory therapy:
- Corticosteroids (methylprednisolone → prednisolone) to reduce immune-mediated edema and prevent paradoxical worsening.
Anticonvulsants:
- Phenytoin or other AEDs for seizure control.

Outcome: Most patients improve clinically and radiologically within months of therapy.

Prognosis

Favorable with early treatment.
Most patients experience resolution of seizures and regression of lesions.
Delayed diagnosis can result in chronic epilepsy, cognitive impairment, or permanent neurological deficits.

Learning Points

Always consider cerebral schistosomiasis in patients with seizures returning from endemic regions.
MRI often shows pseudotumoral lesions with irregular enhancement.
Eosinophilia and exposure history are critical diagnostic clues.
Combination therapy with praziquantel + corticosteroids is highly effective.

Quiz

Q 1. Which MRI feature is most suggestive of cerebral schistosomiasis?

A) Homogeneous contrast enhancement
B) Restricted diffusion on DWI
C) Patchy, irregular gadolinium enhancement with perilesional edema
D) Ring-enhancing lesion with central necrosis

Q 2. Which Schistosoma species most frequently causes cerebral involvement?

A) S. mansoni
B) S. haematobium
C) S. japonicum
D) S. intercalatum

Q 3. What is the cornerstone of pharmacological treatment for cerebral schistosomiasis?

A) Albendazole
B) Ivermectin
C) Praziquantel
D) Amphotericin B

Answer & Explanation

1. Answer: C. Explanation: Cerebral schistosomiasis typically demonstrates irregular patchy enhancement with surrounding edema, unlike abscesses or tumors.

2. Answer: C. Explanation: S. japonicum is the most common cause of cerebral schistosomiasis, particularly in Asia.

3. Answer: C. Explanation: Praziquantel is the first-line antiparasitic agent, often combined with corticosteroids to reduce inflammation.

References

[1] J. F. Ross et al., “Schistosomiasis of the central nervous system,” Lancet Neurology, vol. 11, no. 3, pp. 255–266, 2012.
[2] R. Ferrari et al., “Neurological manifestations of schistosomiasis,” Acta Tropica, vol. 105, no. 2, pp. 79–97, 2008.
[3] J. Lambertucci, “Cerebral schistosomiasis: A diagnostic challenge,” Revista da Sociedade Brasileira de Medicina Tropical, vol. 47, no. 1, pp. 3–9, 2014.
[4] S. Pittella, “Neuroschistosomiasis,” Brain Pathology, vol. 5, no. 2, pp. 143–148, 1995.
[5] World Health Organization, “Schistosomiasis: Key facts,” WHO Fact Sheet, 2022.
[6] J. L. B. Braga et al., “Pseudotumoral form of cerebral schistosomiasis: Imaging features and literature review,” Neuroradiology Journal, vol. 33, no. 5, pp. 411–420, 2020.
[7] H. H. Katz, “Management of neuroschistosomiasis,” Current Opinion in Infectious Diseases, vol. 34, no. 5, pp. 475–482, 2021.

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