Expect the unexpected: a case of isolated eosinophilic meningitis in toxocariasis

Clinical spectrum of symptoms in cerebral Toxocariasis (Review)

Human helminth zoonosis is one of the most encountered helminthiases worldwide. Representative diseases include Toxocara canis and Toxocara cati, which are common nematodes prevalent in dogs and cats. The infiltration of these roundworms in the human body through contaminated food or nematode eggs could lead to central nervous system injury as the roundworms can cross the blood-brain barrier leading to neurotoxocariasis. Among the neurological and neuropsychological disturbances produced by Toxocara infection, in humans, the most representative are meningitis, encephalitis, myelitis and cerebral vasculitis, but asymptomatic central nervous system infection is probably the most prevalent. The present review examines the clinical symptomatology of neurotoxocariasis in case reports in the literature in the last 7 decades (1950-2020). The available evidence was retrieved from PubMed and Medline electronic databases. The present review reports the most prevalent clinical symptomatology in the cases of detected and diagnosed Toxocara infection with neuroinvasion. Thus, the present review aims to raise the awareness of neurological cases of Toxocara infection with the potential to at least establish differential diagnosis of neurotoxocariasis.

Imaging of toxocariasis

Several imaging modalities have now been employed to visualize the manifestations of larval Toxocara infection in hepatic, neurologic, ocular, renal, and other anatomical sites. This report reviews the usefulness and value of these individual imaging methods in diagnosis and follow-up of the different cases causing eosinophilic (granulomatous) infiltrations the liver, lungs, brain, heart, and eyes. Imaging provides a means of assisting in diagnosis and management in this infection where diagnosis by biopsy is often unlikely to capture an actual larva for the purpose of making a definitive diagnosis on the basis of larval morphology or DNA detection.

Toxocariasis and the clinical spectrum

Toxocara canis and T. cati are among the most widely distributed helminthic species in the world with a high zoonotic impact. Millions of people are infected^a and hundreds of thousands are suffering from toxocarosis, a disease encompassing four different entities: larva migrans visceralis (VLM) syndrome, ocular larva migrans (OLM) syndrome, covert toxocarosis (covT), common toxocarosis (comT) and neurotoxocarosis (NT). Toxocara infections in humans may remain clinically inapparent but may also induce severe diseases. This contribution gives a synoptic overview of the most important historical, clinical, diagnostic and therapeutical aspects of toxocarosis in humans.

Clinical and Magnetic Resonance Imaging Findings of Neurotoxocariasis

Human toxocariasis is one of the most prevalent helminthiases worldwide. Toxocara canis larvae can cross the blood-brain barrier leading to the neurotoxocariasis. The clinical presentation consists of a wide spectrum of neurological manifestations, but asymptomatic infection is probably common. Neurotoxocariasis is not a frequent diagnosis probably due to the non-specific nature of its symptoms as well as the lack of confirmatory diagnostic tests. Diagnosis of neurotoxocariasis is based on the presence of a high titer of anti-Toxocara antibody in the cerebrospinal fluid or in the serum, presence of eosinophilia in the serum or cerebrospinal fluid, and clinical and radiological improvement after anthelmintic therapy; however, universally accepted diagnostic criteria are lacking. Magnetic resonance imaging (MRI) findings include single or multiple, subcortical, cortical or white matter hyperintense lesions, best visualized on FLAIR and T2-weighted imaging, and usually isointense or hypointense on T1. These imaging findings are suggestive but not specific to neurotoxocariasis. Definitive diagnosis is made by histological confirmation, but it is rarely followed. This review provides an overview of the clinical manifestations, management options, and MRI findings of neurotoxocariasis.

Neurotoxocariasis: a systematic literature review

PURPOSE

Toxocariasis is a widespread zoonosis, which may result in central nervous system injury.

METHODS

We conducted a systematic literature review in MEDLINE, SciELO, ScienceDirect and Google Scholar up to April 2015 using a combination of the following search terms: "neurotoxocariasis" or "neurotoxocarosis", "toxocariasis" or "toxocarosis" and "cerebral" or "neurologic".

RESULTS

One hundred cases of neurotoxocariasis were identified in literature. The majority of patients were male (58 %), with a median age of 42 years. The predominant clinical pictures were myelitis (60 %), encephalitis (47 %) and/or meningitis (29 %). Fever was inconstant (23 %). The suspected mode of transmission, mentioned in only 49 % of cases, was mainly contact with dogs and/or cats (67 %) and ingestion of contaminated food (31 %). Diagnostic imaging examinations found hypodense lesions in cerebral scanner sequences and hyperintense lesions in cerebral MRI T2-weighted sequences in 65 and 57 % of encephalitis cases respectively, and in 92 % of myelitis cases in medullary MRI T2-weighted sequences. The detection of antibodies against Toxocara spp. was almost constant in blood and cerebrospinal fluid (CSF), 99 and 93 %, respectively. The two most commonly used drugs were corticosteroids (72 %) and/or albendazole (68 %) for a period of at least 3 weeks, which often needed to be repeated. Despite a low mortality rate (6 %), complete remission was observed in only 40 % of cases.

CONCLUSIONS

Neurotoxocariasis, a completely preventable zoonosis, could lead to severe sequelae failing prompt diagnosis. A compatible clinical picture, presence of risk factors, blood eosinophilia and high titers of antibodies against Toxocara spp. in CSF should alert physicians.