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| Introduction Human eysticercosis is infection by the larval (cysticercus) stage of the tapeworm T solium. Prevalence rates to 10% are recognized in some endemic areas. The natural history of the infection is incompletely known. Cysticerci complete their development within 2-4 months after larval entry and live for months to years. Several factors give rise to symptomatology: Initially, the live larva within a thin- walled cyst (vesicular cyst) is minimally antigenic. When the host immune response or chemotherapy results in gradual death of the cyst, there may be cyst enlargement (colloidal cyst) with mechanical compression, inflammation with pericyst edema, and (sometimes) vasculitis that can result in small cerebral infarcts, increased intracranial pressure and cerebrospinal fluid changes may follow. Subsequently, as the cyst degenerates over 2-7 years, it may disappear or be replaced by a granuloma, calcification, or residual fibrosis. Cysts at different life cycle stages-active (live), transitional, and inactive (dead)-may be present in the same organ. Although some patients develop an intense immune response to the parasite, others show a remarkable tolerance. Locations of cysts in order of frequency are the central nervous system, subcutaneous tissues and striated muscle, globe of the eye, and, rarely, other tissues. Cysts reach 5-10 mm in soft tissues but may be larger (up to 5 cm) in the central nervous system. Attached to the inner wall of the cyst is an invaginated protoscolex with four suckers and a crown of hooks. Clinical findings Signs and symptoms: Neurocysticercosis In many patients, cysts remain asymptomatic. When symptomatic, the incubation period is highly variable (usually from 1 to 5 years but sometimes shorter). Manifestations are due to mass effect, inflammatory response, or obstruction of the brain foramina and ventricular systems. Neurologic findings are varied and nonspecific, in large part determined by the number and location of the cysts. . Acute invasive stage-This rare event, occurring shortly after invasion, results from extensive acute spread of eysticerei to the brain parenchyma. Fever, headache, myalgia, marked eosinophilia, and coma may occur. . Parenchymal cysts-Cysticerci can present singly or multiply and may be scattered or in clumps. Findings include epilepsy (focal or generalized), focal neurologic deficits, intracranial hypertension (intense headache, vomiting, papilledema, visual loss), and altered mental status. Seizures usually do not occur until the cyst or cysts have begun to die. . Subarachnoid space cysts and meningeal cysts-Small to large cysts are generally located in the cortical sulei or basal cisterns. The arachnoid is the principal basal membrane affected. Adhesive arachnoiditis may result in obstructive hydrocephalus, intracranial hypertension, arterial thrombosis leading to transient ischemia or stroke, and cranial nerve dysfunction (most often of the optic nerve). . Ventricular cysts may float freely (usually singly) within the ventricles or cerebral aqueduct or may be attached to the ventricular wall. They are usually asymptomatic but can cause increased intracranial pressure as a result of intermittent or total blockage. . Racemose cysts are rare aberrant forms that are multiple-branched, noneneysted, and lack a scolex; they present as grape-like irregular clusters and may reach over 10 cm in diameter. They generally are found in the ventricular and basal subarachnoid spaces, where they cause marked adhesive arachnoiditis and often-obstructive hydrocephalus. . Spinal cord cysts can be extraspinal or intraspinal and cause arachnoiditis (meningitis, radiculopathy) or pressure symptoms. Ophhthalmocysticercosis Usually there is a single cyst, ftee-floating in the vitreous or under the retina. Presenting symptoms include periorbital pain, scotomas, and progressive deterioration of visual acuity. Findings may include disk hemorrhage and edema, retinal detachment, iridocyclitis, and chorioretinitis. MRI but not CT may assist in diagnosis; immunologic tests are negative. . Subcutaneous and striated muscle cysticercosis Subcutaneous cysts present as nodules that tend to appear, collapse and disappear, and then reappear in other sites after variable periods of time. They are usually asymptomatic.
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