Parasitic Infections
Major public health problem in tropical and less developed countries. Predisposing factors: poor living conditions; appropriate climate for vectors to facilitate transmission; immunosuppression. Diseases caused by worms (helminths), protozoa.
Helminthic Infection
Frequent systemic allergic responses (e.g., eosinophilia). Nervous system involvement more often focal than diffuse.
Cysticercosis
Encystment of larvae of Taenia solium (pork tapeworm), in tissues. Acquired by ingestion of ova by: (a) fecal contamination of food; (b) autoinfection via anal-oral transfer; (c) reverse peristalsis of proglottids into stomach. Ingestion of infected pork results in adult tapeworm infection, not in cysticercosis.
Epidemiology
Most common parasitic infection of CNS. CNS involved in 50–70% and in virtually all symptomatic patients.
Common in Mexico, Central and South America, Southeast Asia, China, India. Increasing in the United States.
Symptoms and Signs
Depend on cyst location. Common: seizures (cerebral cortex), headache (increased intracranial pressure due to edema), meningitis (meningeal spread). Also: obstructive hydrocephalus (third or fourth ventricle), stroke (cerebral vessels).
Investigations
CT, MRI: hydrocephalus; cyst (MRI) or cyst calcification (CT); enhancement of cyst with intravenous contrast.
Plain radiographs of thighs and calves: multiple cigar-shaped calcifications.
CSF: normal or moderate pleocytosis, elevated pressure. Meningeal form: hundreds to thousands of white blood cells (WBCs) (usually mononuclear), high protein, low glucose.
Antibody to tapeworm usually positive in serum, CSF.
Treatment
Hydrocephalus: ventricular shunting. Seizures: anticonvulsants. Intractable seizures: consider surgical removal of cysts. Meningitis: corticosteroids used, but benefit not proven.
Eradication of infection: albendazole, with corticosteroids during first week of treatment to reduce inflammation due to dying cysts. Indications for eradication of infection ocontrversial.
Echinococcosis (Hydatid Cysts)
Caused by larvae of Echinococcus granulosus (dog tapeworm). Most common in children in rural areas in countries where herd dogs assist in sheep and cattle raising.
Cysts most common in liver, lungs. Brain involved in 2% of cases. Neurologic symptoms may develop with cysts in skull or spine. Cerebral cysts usually single. Most common in cerebral hemispheres.
Symptoms and Signs
Dictated by location of cyst. Seizures, increased intracranial pressure may also occur.
Investigations
CT, MRI: single, nonenhancing cyst of CSF density. Needle biopsy avoided; may cause anaphylaxis from cyst rupture. In spinal disease, vertebral collapse common. Eosinophilia uncommon except after cyst rupture. Liver enzymes usually normal. Serologic tests positive in 60–90% of infected people.
Treatment
Complete surgical removal without puncturing cyst. Albendazole used to: 1) reduce cyst size; 2) prevent secondary hydatidosis at time of surgery. Albendazole alone sometimes curative.
Schistosomiasis (Bilharziasis)
Schistosoma japonicum: cerebral hemispheres; S. haematobium, S. mansoni: more often spinal cord.
Epidemiology
Affects >200 million people worldwide. S. japonicum: Asia and Pacific tropics. S. mansoni: Caribbean, South America, Africa, Middle East. S. haematobium: Africa, Middle East.
Syndromes
Symptom onset may be delayed for 2 years. May relapse. CNS involved in 3% to 5% with S. japonicum.
Acute cerebral schistosomiasis: diffuse fulminating meningoencephalitis with fever, headache, confusion, lethargy, coma. Focal or generalized seizures, hemiplegia, other focal signs also common.
Chronic cerebral form: localizing signs, increased intracranial pressure with papilledema.
Granulomatous masses in spinal cord: acute onset; signs and symptoms of incomplete transverse lesion. Conus most common site of cord involvement; also granulomatous root lesions.
Investigations
Blood: leukocytosis, eosinophilia. CSF: may be normal; pressure may be increased; slight or moderate pleocytosis (sometimes with eosinophils); increased protein. CT, MRI: cerebral or spinal lesions.
Treatment
Praziquantel. Oral steroids may help. Anticonvulsants for seizures. Surgery for large granulomatous lesions.
Paragonimiasis
Lung flukes (Paragonimus westermani, P. mexicanus). Common in China, Korea, Japan, Southeast Asia, South Pacific areas, Africa, India, Central and South America.
Acquired by eating uncooked or inadequately cooked fresh water crustaceans. Most common symptoms pulmonary, intestinal.
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