In August 2018 a 33-year old woman presented with a history of progressive headache, nausea and vomiting. The patient is of Thai origin but has resided in Switzerland for 6 years. However, she regularly travels to rural north-eastern Thailand, which was also the case prior to onset of symptoms. Two weeks after arrival in Thailand, the patient noted self-limiting diarrhea that was followed by non-specific symptoms (i.e. fatigue, feeling of generalized swelling, leg accentuated weakness). Two weeks after onset of these non-specific symptoms the patient returned to Switzerland and reported symptom aggravation in the form of gradually increasing headache. The initial headache location shifted from the right to the left hemisphere and eventually manifested as holocranial headache of dull-throbbing character. The patient, who denied being prone to headaches, described severe headache (numerical rating scale 7-10) that was not responsive to nonsteroidal anti-inflammatory drugs. Insomnia due to persistence of headache with additional occurrence of nausea and vomiting prompted the patient to attend the emergency department 5 days after returning from Thailand.
On admission, the patient was afebrile (temperature 36,8  C), fully conscious (Glasgow Coma Scale 15) and without focal neurologic deficits or signs of meningism. The medical history revealed a pre-existing, inactive hepatitis B infection and subclinical hypothyroidism. For both conditions no treatment was taken at the time of presentation. From routine screening during a previous pregnancy, HIV was known the be negative. A complete blood count (CBC), clinical chemistry, a lumbar puncture (LP) and cranial computed tomography (CT) was ordered. The CBC indicated a neutrophil predominance and biochemistry results were unremarkable. In the cerebrospinal fluid (CSF) eosinophilia was noted (Table 1), a finding that was not reflected in the peripheral differential count.
A vascular occlusion in the supply area of the right middle cerebral artery compatible with Moyamoya disease was suspected in the CT scan. Magnetic resonance imaging (MRI) was performed, revealing adequate collateral circulation and no evidence for a recent occlusion or active vasculitis. A few age-appropriate non-specific white-matter lesions were seen in both hemispheres but no leptomeningeal nor nodular enhancing lesions.
The pleocytosis (cell count of 1067/muL) in the CSF, and the abnormally elevated absolute and relative eosinophil counts of 267/muL and 25% respectively, led to the diagnosis of EOM (Fig. 2). Considering the travel history, an empirical treatment with albendazole (400 mg, BD) and prednisolone (60 mg OD) was started to cover parasitic EOM. Additionally, serological testing for tissue helminths was ordered and performed at the national reference center at Swiss Tropical and Public Health Institute, Basel, Switzerland alongside other neurotropic pathogens.
Enzyme-linked electroimmunotransfer blot (EITB) for A. cantonensis and Gnathostoma spp specific IgG antibodies performed with serum were nonreactive. IgG screening ELISAs and IgG/IgM/IgA indirect fluorescent antibody tests for Echinococcus granulosus, Fasciola spp., Filaria spp. Schistosoma spp., Strongyloides stercoralis, Trichinella spp and Toxocara spp. as well as screening for other neurotropic pathogens (i.e. Borrelia burgdorferi, Tick-borne encephalitis virus, Treponema pallidum) and HIV were negative. Aside from the afore-mentioned pathogens, the origin of symptoms due to an infection with free living amoeba (FLA) was considered. However, since neither typical features of primary amoebic meningoencephalitis (caused by Naegleria) nor granulomatous amoebic encephalitis (caused by Acanthamoeba) were seen, no molecular or immunologic tests to rule out a FLA infection were requested.
As acute phase Angiostrongylus serology can be negative, the empirical treatment was continued and follow up serology was recommended. The dual anthelminthic and anti-inflammatory therapy led to a marked clinical improvement, and the patient was discharged home after 6 days of hospitalization.
Two weeks after treatment initiation, the patient was seen for a follow up visit in the outpatient department. At this visit, no more symptoms were reported and serologic testing for A. cantonensis and Gnathostoma spp, the two most likely causes of the initial symptoms were repeated. While the latter remained negative, the serological test for A. cantonensis turned positive, indicating seroconversion and, thus confirming the Angiostrongylus-associated EOM. Recommended treatment with albendazole (3 weeks) and prednisolone (2 weeks) was completed and the patient recovered completely.