Myelitis in a Young Patient With Testing Supportive for Both Angiostrongylus and Schistosoma Infection

Schistosoma

Neuroschistosomiasis is a rare complication of Schistosoma infection and prognosis depends on early recognition and treatment. Schistosoma infections are generally asymptomatic or have mild rash, fever, chills, cough, and muscle aches.^1-3 On rare occasions Schistosoma can spread to the central nervous system (CNS) and cause Neuroschistosomiasis, which typically presents with encephalitis if infected with S. japonicum, causing headache, seizure, and altered mental status, or myelitis if infected with S. mansoni or S. haematobium causing weakness, back pain, and urinary retention.^1-4 With myelitis, spinal cord symptoms include lower limb weakness, bowel or bladder dysfunction, lower limb paresthesia, deep tendon reflex abnormalities, and sexual impotence in more than 80% of cases. ⁴

Schistosoma typically occurs in Africa, the Arabian Peninsula, South America, China, Philippines, and Indonesia with various subspecies having predilection for different areas.^1,2 Infection in humans occurs after contacting the parasite that lives in freshwater snails.^1,2

The parasites mature over several weeks inside blood vessels. Some eggs travel to the bladder or intestines and are passed into urine or stool.^1-3 Eggs can embolize to the CNS where they mature into adult forms. ³ The eggs induce local eosinophilic inflammation causing damage, granuloma formation, and eventually fibrosis and demyelination.^1,3

MRI spine may show signal hyperintensity on T2-weighted images, enlargement of the lower spinal cord and conus medullaris, thickened spinal roots, and a heterogeneous pattern of contrast enhancement on T1-weighted images. ⁴

Angiostrongylus

Angiostrongylus is the most common cause of eosinophilic meningitis and usually presents as transient meningitis.^5,6 90% of patients present with a headache and 40%–54% have paresthesias or hyperesthesia.^6,7 Headache is often relieved by LP and patients with paresthesias may experience them for several week.^6-8 Other common symptoms include fever, constipation, neck stiffness, nausea, vomiting, and transient abdominal pain with or without fever.^6-8 Most patients have a self-limited course with complete recovery. ⁷

Angiostrongylus primarily occurs in Southeast Asia with a predominance for Thailand and Malaysia. ⁹ Infection in humans develops after eating infected raw or undercooked snails or slugs or from animals such as crab, freshwater shrimp, or centipedes.^5,9

The worms migrate to the CNS, but do not produce eggs. ⁵ Symptoms resolve as the worms die and the accompanying inflammation resolves. Treatment includes analgesics, corticosteroids, and CSF removal to relieve symptoms of increased intracranial pressure.^9,10 There is debate about the benefit of antiparasitic agents.^9,10

Laboratory findings include peripheral blood eosinophilia in approximately 60%–80% of patients.^4,11,12 There is also generally a CSF eosinophilia that exceeds 10% in 95% of cases. ¹² CSF protein is usually elevated. ⁷ MRI may demonstrate high signal intensities over the globus pallidus and cerebral peduncle on T1-weighted imaging, with multiple enhancing nodules in the brain and linear enhancement in the leptomeninges. ¹³

Clinical Decision Making

This case highlights the importance of considering a broad differential diagnosis in patients with atypical presentations of myelitis and eosinophilic CSF. This patient had a presentation that may be due to infection with Angiostrongylus and false positive Schistosoma serologies but could be from minimally symptomatic Schistosoma infection (likely without neurologic involvement) concurrent with Angiostrongylus infection. Early in his course, the clinical picture and positive Schistosoma serology seemed to fit the diagnosis of Neuroschistosomiasis, however the treatment team was unsatisfied with this diagnosis in isolation. In particular, the level of spinal cord involvement, cervico-thoracic rather than lumbosacral, was more suggestive of infection with Angiostrongylus cantonensis which often presents similarly. Additional factors such as travel to Southeast Asia, migratory pain, and rash also suggested Angiostrongylus as the primary causative agent and the diagnosis was confirmed with molecular testing. Despite the initial concern about Schistosoma, the lack of typical findings associated with Neuroschistosomiasis makes Angiostrongylus the more likely etiology for his myelitis, especially given Schistosoma serology can be falsely positive when cross reactive with other helminths including Angiostrongylus. ¹⁴ He also had a negative stool O&P and negative urine screens for Schistosoma which continued to make the diagnosis of schistosomiasis less likely, however, given the treatment team was unable rule out this diagnosis completely, anti-parasitic treatment was prudent.

Patients often need to be treated without definitive testing given how long it takes to get results. Fortunately for him, treatment of both conditions with pulse dose steroids was indicated to decrease severity and length of symptoms and aid in recovery.^1,10,15 Definitive therapy with antiparasitic agents for schistosomiasis is indicated after pulse dose steroids to reduce the risk of paradoxical reaction.^1,10 The benefit of antiparasitic treatment for Angiostrongylus is currently debated and should be decided based on shared decision making with the patient. ¹⁵ Ultimately, this case highlights the complexity of diagnosis of parasitic infections particularly when lab results are inconclusive or when cross-reactivity between different helminths complicates the interpretation. The clinical lesson here is the importance of evaluating all potential infectious causes, including co-infections, and being cautious of overreliance on a single serologic result when faced with an evolving clinical picture.

Conclusion

Patients with demyelinating or inflammatory appearing CNS lesions, recent travel history, or atypical findings should be considered for workup for CNS helminths. Eosinophilic CSF Pleocytosis may further narrow the differential diagnosis for helminth infections, and a thorough travel history can help identify possible causative agents of concern. A single serologic test may be unreliable given possible cross reactivity, so a thorough diagnostic workup to evaluate for all potential etiologies, even with positive laboratory results for one pathogen, is important to evaluate and treat patients with an atypical presentation.