Cerebral gnathostomiasis

Clinical record

A previously well, 42‐year‐old man presented to an Australian hospital with a 4‐day history of sudden onset, bilateral, occipital headache, 4 weeks after returning from a holiday in Thailand. He had consumed duck blood while travelling in Asia, but had eaten no raw or undercooked meat or seafood. His physical examination was normal with no evidence of neurological dysfunction and he had no rash or skin swellings. Blood tests revealed a peripheral blood eosinophilia of 4.89 × 10⁹/L (reference interval [RI], < 0.6 × 10⁹/L) but were otherwise normal. Computed tomography of the brain was unremarkable. Cerebrospinal fluid examination showed 30 × 10⁶/L red blood cells (RI, < 5 × 10⁶/L) and 1120 × 10⁶/L white blood cells, 80% of which were eosinophils (RI, < 5 × 10⁶/L). Magnetic resonance imaging (MRI) of the brain demonstrated non‐specific T2 hyperintensities in the subcortical white matter (Supporting Information) and normal T1‐weighted post gadolinium images (Box 1, A). However, susceptibility‐weighted images showed serpiginous tracts in both occipital lobes (Box 1, B). Cerebral gnathostomiasis was suspected and daily oral prednisolone at a dose of 60 mg was prescribed. His headache improved and he was discharged home. Four days later, he re‐presented with right‐sided upper limb weakness and mixed dysphasia. Repeat MRI showed significant progression of the tracts (Box 1, C). His corticosteroid therapy was increased to 8 mg dexamethasone three times daily, but antihelminthic agents were not prescribed as there was concern that dying larvae might migrate further or lead to cerebral oedema. His corticosteroids were subsequently weaned, and his neurological deficits gradually improved over one month. Blood that had been sent to Thailand for serological testing during his first hospital admission returned a positive result for gnathostomiasis. Sixteen months after his initial presentation, he had made an excellent neurological and functional recovery, with only a subtle short term memory deficit. Repeat MRI performed at this time revealed persistent, but stable, changes with no new tract formation (Box 1, D).

Discussion

Gnathostomiasis is caused by the migrating third‐stage larvae of Gnathostoma species nematodes and is endemic in Asia, particularly Thailand. The infection is usually acquired by eating raw second intermediate or paratenic hosts that include freshwater fish and poultry. Patients may present with cutaneous swellings, visceral larva migrans and occasionally eosinophilic meningoencephalitis. The characteristic MRI findings of cerebral gnathostomiasis are diffuse, poorly defined hyperintense lesions on T2‐weighted images, although their appearance may resemble the abnormalities seen in other inflammatory conditions such as multiple sclerosis.1 In our case, susceptibility‐weighted images — a sequence sensitive to blood product deposition — clearly showed serpiginous tracts caused by microhaemorrhages produced by the migrating larvae. Angiostrongylus cantonensis — the most common parasitic cause of eosinophilic meningitis — is also endemic to South‐East Asia and is an important alternative diagnosis. However, in such cases, brain imaging is usually normal or shows non‐specific meningeal enhancement.2 Several other parasites may cause eosinophilic meningitis, but these are usually distinguishable from cerebral gnathostomiasis radiologically2,3 (Box 2). Serological testing can differentiate between Gnathostoma and A. cantonensis but is not readily available and is only performed in a few countries. The treatment of cerebral gnathostomiasis is predominantly supportive, although corticosteroids can be used to suppress inflammation and reduce brain oedema. The role of antihelminthic treatment with albendazole or ivermectin is incompletely defined as there are no randomised control trials that might inform optimal management strategies. Improvement with antihelminthic therapy has been reported; however, these agents may also cause harm if dying larvae induce cerebral oedema.4,5 In our case, corticosteroids were started promptly, antihelminthic therapy was withheld, and the patient had an excellent outcome. Clinicians caring for patients with eosinophilic meningitis should consider the use of MRI with susceptibility‐weighted images as an aid to diagnosis and can be reassured that patients with cerebral gnathostomiasis may experience complete recovery without antihelminthic therapy.

Box 1 – Axial magnetic resonance brain imaging in cerebral gnathostomiasis

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A: T1‐weighted post gadolinium images revealed a normal appearance. B: Susceptibility‐weighted images showing serpiginous tracts in bilateral occipital lobes traversing the splenium of the corpus callosum (arrow). C: Repeat susceptibility‐weighted images showing progression of the tracts now involving the left parietal and frontal lobes (arrows). D: Susceptibility‐weighted images performed 16 months after initial diagnosis revealed persistent but stable changes with no new tracts.