Neurocysticercosis
Abstract & Commentary
By Joseph E. Safdieh, MD, Assistant Professor of Neurology, Weill Medical College, Cornell University. Dr. Safdieh reports no financial interest in this field of study.
Synopsis: Single cysticercal granulomas are more common in patients with lesser degrees of exposure to T. Solium eggs and these granulomas likely represent cysts that were killed by the host immune system early after infection.
Source: Garcia HH, et al. Neurocysticercosis: Unraveling the nature of the single cysticercal granuloma. Neurology 2010;75:654-658.
T. solium infection and neurocysticercosis (ncc) are endemic in most developing countries and are being diagnosed with increasing frequency in industrialized countries due to tourism and immigration patterns. Humans are the definite host, and both pigs and humans can serve as intermediate hosts. Humans acquire T. Solium infection by ingesting infected pork. The infection is then transmitted by fecal-oral transmission through transmission of T. solium eggs. The embryos from these eggs are liberated by gastric acid secretion, crossing the intestinal wall and lodging in various end organs including brain, heart, and muscle. The infection establishes and encysts, reaching a full size of about 1 cm in 2-3 months. NCC presents with seizures in 50%-90% of symptomatic patients and disorders of intracranial pressure and hydrocephalus develop in 20%-30% of symptomatic patients.
After entering the central nervous system, cysts develop and elicit few inflammatory changes in the surrounding tissue, likely due to protection from the innate immune system by the blood-endothelial barrier. Symptoms often do not occur for an extended period of time after establishment of the cyst. This has been demonstrated in British soldiers returning from India to England, where symptoms of NCC developed 3-5 years after last possible exposure. This observation led to the prevalent viewpoint that symptoms of NCC develop after detection of an active cyst by the innate immune system or the administration of anti-parasitic therapy.
In some patients, NCC presents as a single cysticercal granuloma, which is a non-calcified ring enhancing small (1 cm) lesion detected on CT or MRI at the time of symptomatic presentation. This presentation is more common in returning travelers and in the Indian subcontinent where pig exposure is lower and the inoculum tends to be lower. In Central and South America, single cysticercal granulomas are a rare presentation. Single cysticercal granulomas have been demonstrated histologically to represent degenerating cysts, likely due to detection by the immune system. Most of these lesions resolve spontaneously after 1 year, leaving a calcified scar in 20%. Most patients with single cysticercal granulomas will not have a recurrent seizure. These lesions are likely in the process of destruction by the host immune system.
Commentary
Most U.S. neurologists have limited experience treating NCC, although this disease is certainly becoming more of an issue over time. This report is less relevant to patients who are from Central and South America, where multilesional involvement is more common. However, this is an important report for neurologists treating American patients who acquire the infection, as the inoculum tends to be lower. These patients may present years after exposure with a seizure and a single ring enhancing CNS lesion. Usually, this will lead to an expensive systemic neoplastic workup and possibly a brain biopsy. Often a recent travel history is negative, but clinicians should ask about a more remote travel history as well. The clinical suspicion for NCC should always be present because if this diagnosis can be made non-invasively with serum and cerebrospinal fluid antibodies, the patient can be spared a brain biopsy. Patients with single cysticercal granulomas generally have a good prognosis and may not require long term anti-epileptic drug therapy.
Single cysticercal granulomas are more common in patients with lesser degrees of exposure to T. Solium eggs and these granulomas likely represent cysts that were killed by the host immune system early after infection.You have reached your article limit for the month. Subscribe now to access this article plus other member-only content.
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