September 2014

A 31 year-old Hispanic male presents to the Emergency Department with a chief complaint of headaches for the past 2 months

David Cantu M.D., Rocco LaSala M.D. and Kym Gyure M.D.

Overview

The patient is a construction worker from Guatemala who has been living in the United States for the past 12 years.  He has no significant past medical history and denies any recent international travel or sick exposures.

During the past two months, the patient has experienced several episodes of headaches, vomiting and dizziness.  The headaches were initially intermittent and localized to the top of the head but eventually progressed to a constant sharp sensation.  He further explains that for the past week he’s been having episodes of double vision.  He denies fever, chills, seizures or loss of consciousness. Physical examination is unremarkable, including absence of nuchal rigidity.

Gross Description

His initial laboratory testing, including CBC, liver and pancreas function tests, serum electrolytes, urinalysis and coagulation studies are without abnormalities.  A CT scan reveals moderate hydrocephalus with suggestion of obstruction within the fourth ventricle.  Cranial MRI confirms the presence of a non-calcified, uniloculated cystic lesion arising within the inferior fourth ventricle at the level of the obex (Image 1).  The need for alleviation of intraventricular pressure prompts neurosurgical intervention and excision of the cystic structure.  Histopathologic sections confirm the diagnosis.

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Image 1
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Image 2 (100X, H&E)
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Image 3 (400X, H&E stain)

Diagnosis

How is this infection Aquired ?

Answer

Please select an answer above.

Discussion

Neurocysticercosis is the most frequent neuroparasitosis in the world, affecting millions of people worldwide.  It is more prevalent in developing countries and areas where hygiene is poor.  In the United States, it is most frequently found in the Southwest. [2] 

The most common clinical manifestation of neurocysticercosis is seizures, which may be the only manifestation in up to one third of cases.  Cysticercosis is an important cause of adult-onset epilepsy in endemic areas.  As illustrated in the present case, intraventricular cysts may also produce obstruction of the cerebrospinal fluid flow causing hydrocephaly.  This is accompanied by changes in personality and mental status in up to 40% of patients.[4]   The characteristic finding on CT scan is the presence of one or more calcified cysts, which may show ring enhancement.  Lesion(s) present within the ventricle or subarachnoid space may not be visible by CT scan.[5]  Rarely, an invaginated protoscolex may be clearly noted on cranial MRI (Image 1b, arrow). 

The life cycle of T. solium is comprised of transmission between definitive hosts (humans) and intermediate hosts (pigs). Humans become infected by consumption of undercooked muscular tissues of the intermediate host, which contain viable cysticerci.  Over the course of a few weeks, these cysticerci develop into an adult tapeworm in the human intestine.  Here, each gravid proglottid can produce up to 50,000 eggs, which are released during defecation and ultimately ingested by the intermediate host.  On occasion, an accidental host such as humans may ingest these ova, producing cysticercosis.  Upon ingestion, an ovum releases the oncosphere, which penetrates the intestinal wall and gains access to the lymphatic vessels and bloodstream.  From here, an oncosphere may lodge in variety of tissues but most commonly affects skeletal muscle, eye and brain.[3]  Whatever the visceral site, an oncosphere encysts, forming a cysticercus.  The living cysticercus may produce an immune reaction that ultimately leads to formation of a fibrous capsule. If the organism dies, which commonly occurs within 2 years, an increased inflammatory reaction is elicited and calcification results. 

Diagnosis of human cysticercosis is made based on visualization of the organisms (e.g. radiographically by CT or MR or histologically in resected tissue) and/or by antibody testing.  Among the latter, both enzyme-linked immunostransfer blot (EITB) and enzyme-linked immunosorbent assay (ELISA) techniques are available.  EITB detects antibodies in an immunoblot that incorporates a fraction of lentil-lectin affinity-purified cysticercus glycoprotein.  EITB has higher specificity and sensitivity than ELISA.[1]  Due to cross-reactivity with other helminthes (i.e. specificity <100%), a definitive diagnosis of cysticercosis may depend on identification of the organism radiographically or through direct examination of resected material.[1]  Histologic features of intact cysticerci include a cyst wall composed of a thin tegument with microvilli and underlying myxoid matrix and a single invaginated scolex.  The neck region (Image 3) is comprised of thick tegument with underlying smooth muscles but no microvilli.  The rostellum of the scolex features 4 suckers and 22 - 36 hooklets, though serial sectioning through the block may be required to visualize these structures.[1]  Numerous calcaereous corpuscles are present in the scolex parenchyma (image 3).

Treatment options include praziquantel and albendazole.  Albendazole is the drug of choice in cases affecting the central nervous system.  When the cysticercus dies, it elicits an inflammatory reaction, which can be severe.  Therefore, the use of steroids is recommended when administering antiparasitic therapy.  Prevention can be achieved by properly cooking and freezing all meats and keeping pigs away from contaminated human feces. [1]

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Image 2 – Low power view of slightly tangential section through a scolex surrounded by fibromixoid tissue of the cyst wall. A portion of one sucker is visible (arrow) although no hooklets were apparent in this section.
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Image 3 – High power view of the neck region. Note the thick tegument (large arrow) with underlying smooth layer (small arrow) and scattered calcareous corpuscles (arrow heads).

References

  1. Meyers WM, Neafie RC, Marty AM, Wear DJ. Pathology of Infectious Diseases Volume I Helminthiases 2000; 7:117-136.
  2. Prayson R. Neuropathology 2nd Edition 2012; 7:365-6.
  3. Mahon CR, Manuselis G. Textbook of Diagnostic Microbiology 2nd Edition 2000. 24:811-2.
  4. Winn W, Allen S, Janda W, Koneman E, Procop G, Schreckenberger P, Woods G. Koneman’s color atlas and textbook of diagnostic microbiology 6th Edition 2006. 22:1281-4.
  5. Davis, LE. “Neurocysticercosis” Emerging Neurological Infections. 2005. 261-287.