FINAL DIAGNOSIS: NEUROCYSTICERCOSIS.
Neurocysticercosis, infection of the central nervous system (CNS) by larvae of the pork tapeworm Taenia solium, is the most common neuroparasitic infection in humans (1, 2). It has a worldwide distribution but is most common in Central and Latin America, Mexico, Asia, Africa, Spain, Portugal, and Eastern Europe. Most infected patients in industrialized nations are immigrants from endemic regions (1).
Humans are the only definitive hosts of T. solium. Infection is aquired by different routes (3). In the usual or benign life cycle, humans are infected by eating measly pork (pork which is infected by viable larvae or cysticerci). The ingested cysticerci attach to the jejunum where they mature into adult tapeworms. The tapeworm sheds gravid proglottids into the stool. If contaminated food is ingested by the pig then the eggs hatch, burrow through the pig's gastrointestinal tract, enter the circulation, and encyst in systemic tissue, including the brain, where they develop into the larval or cysticercus form. The life cycle is then complete, with the human acting as definitive host and the pig as intermediate host. Humans, however, may become accidental intermediate hosts by ingesting products which are fecally contaminated with T. solium eggs, either shed in a food handler's feces or in their own feces if they are infected by the adult tapeworm. If the resulting larvae encyst in the brain, neurocysticercosis develops. Cysticercosis in humans only develops by this aberrant mechanism.
The clinical presentation is highly variable and can mimic virtually any disease of the CNS, depending upon the number, size, and location of the cysts (4). In endemic regions neurocysticercosis is a common cause of seizures and should be included in the differential diagnosis of epilepsy (5). Subarachnoid lesions may cause meningitis, while intraventricular or aqueductal lesions may lead to hydrocephalus (1). Signs of increased intracranial pressure such as headache, vomiting, and confusion, may be present. An increased risk for cerebrovascular accidents has been reported (6).
The presenting CNS symptoms are highly dependent upon the host immune response (1, 3). Enlarging cysticerci may exert a mass effect but as long as the larvae are viable there is relative immune tolerance and minimal inflammatory response. Many patients with viable cysticerci are therefore asymptomatic. Antigen exposure, however, occurs when the larvae degenerate. This leads to an acute inflammatory response with numerous eosinophils and edema. The inflammation subsequently becomes granulomatous and finally forms a fibrous scar. The cysticerci undergo progressive involution during this process. By the stage of fibrous scarring, only fragmented hooklets may be seen, or no identifiable structures may be present within the cystic scar.
The treatment of neurocysticercosis has evolved from surgical therapy in the past to anticysticercal chemotherapy (2). Both praziquantel and albendazole reduce or even eliminate the cysticerci. Courses of albendazole for as short as 8 days have been reported to be effective. However, increased symptoms occur in some patients because death of the larvae stimulates the host inflammtory response. Concurrent steroid treatment may be given to alleviate these symptoms. This patient did not receive medical therapy because his temporal lesion had been grossly excised, a follow up MRI scan of the brain did not reveal additional lesions, and he was asymptomatic.
Contributed by Susan Abraham MD, Andrew Lieberman MD, PhD, Allison Pack MD, Kevin Judy MD, Gregg Wells MD, PhD, and Zissimos Mourelatos MD