A 28-year-old man presents to the ED complaining of three months of right-sided headache. He says it feel like someone is “poking” him in the occipital area.
He experiences these episodes up to 10 times a day, and each lasts a few minutes and resolves with ibuprofen.
He denies any other symptoms. He has a normal neurological examination, but is demanding a brain CT because he knows “there is something wrong” with his head. Here is what his brain CT shows.
What is the diagnosis? See p. 16.
Neurocysticercosis is an infection of the neurological system after exposure to the pork tapeworm, Taenia solium. Tapeworm (helminthic) infections were documented by the ancient Egyptians and Greeks. (Taenia Solium Cysticercosis: From Basic to Clinical Science. Wallingford, Oxfordshire, UK: CABI Publishing, 2002.)
Some have postulated that pork tapeworm infections were the reason that consuming pork was originally forbidden by Muslim and Jewish law. Cysticercosis infections are endemic to China, Latin America, Southeast Asia, sub-Saharan Africa, and India with currently approximately 2.5 million people infected. Neurocysticercosis is the most common parasitic disease of the nervous system worldwide and the leading cause of acquired epilepsy in children and adults worldwide. (Clin Microbiol Rev 2002;15:747; Rev Neurol 2004;39:924.) Once a disease primarily of developing countries, it has become increasingly prevalent in developed countries because of increased immigration, such as in the southern United States. (Neuroepidemiology 2012;39:145.)
Taenia solium is a foodborne disease transmitted by the fecal-oral route via a two host biological cycle. The pig is an intermediate host, and the human is the definitive host. T. solium embryonated eggs (ova) and gravid proglottids (larvae) from contaminated human feces are consumed by pigs via contaminated food or water. These ova hatch, penetrate the intestinal wall of the pig, and then circulate via the bloodstream into the muscle of the pig where the oncosphere develops into cysticerci in the pig muscle. This process can take months to nearly a decade. (Emerging Neurological Infections. Boca Raton, DL: Taylor & Francis Group, 2005.)
When a human consumes contaminated undercooked pork, the cysticerci develop into a mature tapeworm in the small intestine. The mature tapeworm has a head/scolex that contains four suckers, two rings of hooks, and a multisegmented body, and each hermaphroditic segment is capable of massive progeny production. It sheds nearly 250,000 eggs per day into the host's feces. This condition is known as cysticercosis or taeniasis. The mature tape worms can become an impressive 10 meters or longer, but the disease does not progress beyond this point.
The life cycle continues when a human accidentally ingests the larva or eggs from an exogenous source (either from self-infection or from another infected human via fecal water or food contamination). The T. solium eggs are then digested in the stomach, and the released larva penetrate the intestinal wall and travel via the bloodstream to any organ and develop into cysticerci. They deposit preferentially, however, in the subcutaneous tissue, eyes, and brain.
The presentation of cysticercosis depends on the tissue affected. Cysticerci in the muscle can result in myositis, which can progress into localized calcifications and at times lead to muscle fibrosis and atrophy. Most are asymptomatic, however. Cysticerci in the subcutaneous tissues result in painful mobile cysts found primarily on the extremities and trunk. (J Am Acad Dermatol 1991;25[2 Pt 2]:409.)
Cysticerci cysts can form in many different neurological tissues — the brain (neurocysticercosis), the spinal cord (spinal neurocysticercosis), within the ventricles of the brain (intraventricular neurocysticercosis), or the subarachnoid space (racemose neurocysticercosis). Racemose neurocysticercosis has the highest mortality rate, more than 20 percent. (Brain 1952;75:1.) Spinal neurocysticercosis is rare, but may present with weakness, paresthesias, or radicular back pain. Ocular cysts can form in the globe, subconjunctiva, and extraocular muscles of the eye, and result in monocular visual impairment or blindness.
Patients with neurocysticercosis typically present with seizure (approximately 70%). (Neurology 1992;42:389.) Patients can also present with an insidious onset of symptoms including neuropsychiatric dysfunction, progressive dementia, or a complaint of chronic headache. Chronic headaches may be the result of chronic meningitis, vasculitis, brain edema, or slowly progressive intracranial hypertension from obstructive hydrocephalus. Nearly one-third of obstructive hydrocephalus is secondary to inflammation and fibrosis. The presentation of neurocysticercosis depends on the number of lesions, the parasitic burden, lesion location, and the host's immune response. (Trop Doct 2008;38:192.) Up to 20 percent of patients with neurocysticercosis will have an abnormal neurological finding.
The differential diagnosis of neurocysticercosis is extensive, and includes the differential diagnosis of the space-occupying neurological lesions (tumor or abscess), dementia, meningoencephalitis, stroke, psychosis, and seizure.
The diagnosis of taeniasis is made by localizing ova in stool samples, but only 10 to 15 percent of patients with cysticercosis are infected with an intestinal tapeworm, so stool studies are often not helpful. (Am J Trop MedHyg 1998;59:902.)
The diagnosis of neurocysticercosis is primarily made by neuroimaging, and is not uncommonly an incidental finding. Brain CT findings depend on the stage of infection. Calcified lesions tend to represent dead or involuted nonactive parasitic infection. MRI is the imaging modality of choice to fully characterize neurocysticercosis lesions.
Cerebrospinal fluid (CSF) findings vary depending on the stage of infection and location of the lesions. A lesion fully localized in the brain parenchyma may result in normal CSF with no identifiable parasites. CSF findings of an acute infection can include increased protein, eosinophilia (also seen in the serum), increased IgG index, and mononuclear pleocytosis. Confirmatory testing of the CSF is enzyme-linked immunosorbent assay (ELISA) or serum enzyme-linked immunoelectrotransfer blot (EITB) assay. An immunodiagnostic test that can be considered a gold standard has not been developed so far. (J Biomed Biotechnol 2011;2011:516042.) Brain biopsy of a lesion is usually not required.
Treatment of neurocysticercosis depends on whether the parasitic cyst is dead or viable, the size and location of the offending lesion, and the patients' clinical presentation. (J Neurol Neurosurg Psychiatry 2008;79:978.) Patients who develop seizures from nonviable neurocysticercosis lesions require treatment with anticonvulsant medications; typically monotherapy is sufficient. Antiparasitic treatment should be given to patients with active parasitic infection. Studies have shown that the frequency of seizures resulting from a viable cystic lesion is improved when treatment with antihelmenthic mediations such as albendazole is given in addition to antiepileptic medications. (Neurology 1992;42:389.)
Patients with evidence of brain edema, vasculitis, or encephalitis are typically given steroids to decrease brain swelling, but the data supporting this are limited. (Expert Rev Neurother 2011;11:1175.) Symptomatic space-occupying lesions require surgical intervention. Asymptomatic patients with cysts found incidentally on imaging may not require specific treatment.
Improved sanitation facilities, better meat inspection programs, and improved hygiene decrease the disease burden in affected developing countries. Prevention of pig cysticercosis infection by vaccination is being studied.
This patient initially denied being foreign-born because he is undocumented, but later stated that he was a native of rural Mexico and immigrated 12 years ago. The CT of his brain performed in the ED demonstrated multiple lesions in left basal ganglia, temporal lobe, and cerebral tissue in addition to some intraventricular lesions and changes consistent with hydrocephalus from the racemose subtype of neurocysticercosis. A ventriculoperitoneal shunt was placed, and the patient was started on steroids, antihelmenthic medication, and an anti-epileptic medication. He was discharged and has not followed up.
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