Cysticercosis laboratory findings

Editor-In-Chief: C. Michael Gibson, M.S., M.D. [1];Associate Editor(s)-in-Chief: Ahmed Younes M.B.B.CH [2]

There is no single gold standard for diagnosing cysticercosis (except for biopsy which is rarely done). Diagnosis is made by combining data from various investigations and suspecting the disease. A set of diagnostic criteria was proposed in 2001 based on combination of epidemiological factors, clinical manifestations, laboratory and radiological investigations.

A set of diagnostic criteria were proposed by Del Brutto et al based on the laboratory and imaging tests. The criteria were modified in 2001 to be:^[1]

The definitive diagnosis consists of demonstrating the cysticercus in the tissue involved. Demonstration of Taenia Solium eggs and proglottids in the feces diagnoses taeniasis and not cysticercosis. While suggestive, it does not necessarily prove that cysticercosis is present. Persons who are found to have eggs or proglottids in their feces should be evaluated serologically since autoinfection resulting in cysticercosis can occur.

• CDC’s immunoblot is based on detection of antibody to one or more of 7 lentil-lectin purified structural glycoprotein antigens from the larval cysts of Taenia solium in an immunoblot format.^[2]
• It is 100% specific and has a sensitivity superior to that of any other test yet evaluated. Serum specimens from 97% of parasitologically confirmed cases of cysticercosis have detectable antibodies. No serum samples from patients with other microbial infections react with any of the T. solium-specific antigens.
• The most important factors identified as determining positive immunoblot reactions are the numbers and stage of development of cysticerci. Cumulative clinical experience has confirmed that in patients with multiple (more than two) lesions, the test has more than 95% sensitivity. Seropositivity in biopsy-confirmed patients with single, enhancing parenchymal cysts was <50%; in clinically defined patients with a single cyst but who were not biopsied, sensitivity was 70%. Seropositivity in serum and CSF of patients with multiple but only calcified cysts was 82 and 77%, respectively.
• In all patients, regardless of their clinical presentation, the immunoblot assay is slightly more sensitive in serum than in CSF specimens: consequently, there is no need to obtain CSF solely for use in the immunoblot assay.

• CDC’s immunoblot is both more specific and more sensitive than enzyme immunoassay (EIA) systems with which it has been compared. Lack of specificity has been a major problem in most EIAs because of cross-reacting components in crude antigens derived from cysticerci; these components react with antibodies specific for other helminthic infections, especially echinococcosis and filariasis. Most partially purified fractions evaluated in an EIA appear to have lower sensitivity than crude antigens and do not necessarily achieve higher specificity. Assays employing crude antigens for the detection of antibody are not reliable for the identification of this disease; all positives and any negative strongly suspected of cysticercosis should be confirmed by immunoblot. Currently available antibody detection tests for cysticercosis do not distinguish between active and inactive infections and thus have not been useful in evaluating the outcomes and prognoses of medically treated patients. Both the CDC immunoblot and an EIA are commercially available in the United States.

• CDC’s immunoblot assay with purified Taenia solium antigens has been acknowledged by the World Health Organization and the Pan American Health Organization as the immunodiagnostic test of choice for confirming a clinical and radiologic presumptive diagnosis of neurocysticercosis.

• Typical antibody reactions in CDC’s immunoblot for cysticercosis. Individual sera from patients with either cysticercosis or echinococcosis were analyzed using the immunoblot for cysticercosis.

• Cysticercosis-specific antibodies react with glycoproteins derived from T. solium cysts. The positions of the seven diagnostic glycoproteins are marked and designated according to their relative mobilities in SDS-PAGE. Sera from patients with cysticercosis react with at least one of the cysticercosis-specific proteins, whereas sera from patients with echinococcosis do not react with any of the seven diagnostic proteins.

Can be used for following the response to treatment but less sensitive than EITB in detecting the disease.^[3]

• Microscopic identification of eggs and proglottids in feces is diagnostic for taeniasis; however, eggs and proglottids are not released into the feces until approximately 2 to 3 months after the adult tapeworm is established in the upper jejunum.
• Repeated examination and concentration techniques will increase the likelihood of detecting light infections. Examination of 3 stool samples collected on different days is recommended to increase the sensitivity of microscopic methods.
• Eggs of Taenia spp. cannot be differentiated; a species determination may be possible if mature, gravid proglottids (or, more rarely, examination of the scolex) are present.

• Analysing CSF for parasitic antigens is one of the minor criteria for diagnosing cysticercosis.^[3]
• Lumbar puncture is contraindicated if there are signs of increased ICP (to avoid brain stem herniation).
• Positive changes in CSF analysis as Increased cells (mainly eosinophils), increased proteins, decreased glucose in additiion to positive immunoassays in CNS analysis (ELISA and complement fixation) are almost only present in extraparenchymal NCC in the ventricles and choroidal plexus. ^[4]

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