Neurocysticercosis (NCC) is a parasitic infection of the nervous system caused by the larvae of the tapeworm Taenia solium, also known as the "pork tapeworm". The disease is primarily transmitted through direct contact with human feces, often through the consumption of food or water containing Taenia solium eggs. These eggs hatch in the small intestine and penetrate the intestinal wall. The larvae can travel to the brain, muscles, eyes, and skin. Neurocysticercosis, caused by Taenia solium larvae, differs from taeniasis, which results from adult tapeworm infection.
Neurocysticercosis manifests with various signs and symptoms, influenced by the location, number of lesions, and immune response. While some people may have no symptoms, others may experience seizures, increased pressure in the skull, cognitive impairment, or specific neurological problems. In severe cases, the condition can be life-threatening.
Diagnosis relies on imaging and blood tests. Neurocysticercosis can be prevented through improved sanitation, education, awareness, de-worming and vaccines for endemic areas. Treatment options depend on cyst viability, the host's immune response, and the location and number of lesions. Symptoms are treated with anti-seizure, antiedema, pain, or anti-inflammatory drugs. Surgery, steroids, or other medications are used to treat intracranial hypertension. Anti-parasitic medications are used for treating earlier stages of the disease. Steroids are used to manage inflammation in the central nervous system. Surgery can be used to remove cysts.
Neurocysticercosis is common in developing regions, such as Latin America, China, Nepal, Africa, India, and Southeast Asia. Although rare in Europe and the US, immigration has increased its prevalence. Taenia solium has been recognized since 1500 BC and found in ancient Egyptian mummies. The first recorded cases of neurocysticercosis were likely in 1558. In the 19th century, German pathologists found similarities between T. solium and cysticercus scolex and discovered that consumption of cysticercus in pork caused human intestinal taeniasis.
Signs and symptoms Neurocysticercosis has a wide range of signs and symptoms, which relate to the location, number of lesions, and immune system's response to the infection. Ranging from asymptomatic to deadly, neurocysticercosis has been referred to as the "great imitator" as it can mimic many other neurological disorders. The most common symptoms are seizures, intracranial hypertension, cognitive impairment, and focal deficits.
+ Manifestations of neurocysticercosis Location Form of the disease Common clinical manifestations Brain parenchyma Vesicular cysts Seizures; sometimes asymptomatic.Colloidal cystsSeizures; vomiting; headache; focal signs.Granulomas/calcificationsSeizures, sometimes reoccurring.Cysticercotic encephalitisSeizures; coma; intracranial hypertension. Subarachnoid space Giant cysts in CSF cisterns Seizures; focal signs; intracranial hypertension; cognitive impairment.Diffuse arachnoiditis (inflammation of the arachnoid)Focal signs; intracranial hypertension.HydrocephalusIntracranial hypertension; cognitive impairment.AngiitisAcute stroke syndromes. Ventricular system Ventricular cysts Focal signs; intracranial hypertensionEpendymitis (inflammation of the ependyma)Seizures; intracranial hypertensionSpinal cordArachnoiditisRoot pain; weakness; rarely meningitisParenchymal cystsMotor and sensory signs below the level of the lesionOtherSuprasellar cysticercosisOphthalmologic and endocrinologic disturbancesOphthalmic cysticercosisVisual loss; extraocular muscle paralysisMuscle cysticercosisMuscle pseudohypertrophy
Seizures
Epilepsy is the most common symptom of neurocysticercosis; neurocysticercosis is the primary cause of late-onset seizures in countries with middle and low incomes. Seizures are more common in parenchymal neurocysticercosis than in other forms of neurocysticercosis; they can occur at any stage of the disease. If neurocysticercosis is left untreated, seizures often persist and recur despite treatment. Seizures are more commonly associated with degenerating cysts, which are often accompanied by swelling, inflammation, nerve damage, and gliosis. They are caused by inflammatory responses in the brain and the space-occupying effect of the cysts. Multiple lesions increase the risk of seizures. Active cysts are associated with first-time seizures while calcified granulomas are associated with chronic epilepsy.
Focal deficits Those with neurocysticercosis can exhibit a variety of specific neurologic symptoms determined by the size, number, and location of the parasites. Pyramidal tract symptoms, such as weakness, Babinski's sign, spasticity, and overactive reflexes are the most common. Sensory impairments, parkinsonian rigidity, involuntary movements, language disturbances, and signs of brain-stem dysfunction can also occur. Focal neurologic symptoms are most commonly seen in those with large subarachnoid cysts compressing the brain parenchyma. Inflammation in the arachnoid layer can cause focal signs, ischaemic strokes caused by intracranial artery blockage, cranial nerve compression, hearing loss, and facial nerve palsy or trigeminal neuralgia. There may also be focal neurological symptoms caused by brainstem damage. Cysticercosis of the spinal cord often causes radicular pain, weakness, and sensory impairments due to localized mass effects or inflammation in the subarachnoid space.
Intracranial hypertension
Intracranial hypertension – a build-up of pressure around the brain – is associated with neurocysticercosis and may be accompanied by other symptoms. More common in extraparenchymal neurocysticercosis, it is most frequently caused by buildup of cerebrospinal fluid (CSF) in the brain. Hydrocephalus can be related to granular ependymitis, compression of the CSF pathways by cysts, cysticercotic arachnoiditis, and inflammation or cysts blocking ventricles. Large subarachnoid cysts and cyst clumps can also cause a mass effect and intracranial hypertension, with or without hydrocephalus. Intracranial hypertension can present as episodic loss of consciousness when moving the head, known as Bruns syndrome; it may be subacute or chronic. Cysticercotic encephalitis, which is a severe type of neurocysticercosis usually affecting younger women and children, can also cause intracranial hypertension. Cysticercotic encephalitis is characterized by seizures, intracranial hypertension, clouding of consciousness, optic disc swelling, headache, reduction of visual acuity, and vomiting.
Cognitive and psychiatric disturbances Cognitive and psychiatric manifestations of neurocysticercosis can range from mild deficits to severe dementia. Episodes of psychosis which involve paranoia, confusion, and violent behaviour have been reported to occur with neurocysticercosis. Some of these episodes could be associated with psychomotor epilepsy or post-seizure psychosis. Other psychiatric symptoms of neurocysticercosis include anxiety, delirium, sensory changes, depression, and personality disorders. Those with neurocysticercosis may exhibit depression, cognitive impairments, or a decline in quality of life.
Other symptoms Spinal arachnoiditis can cause subacute root pain and weakness. Cysts in the spinal cord are typically associated with motor and sensory impairments that vary depending on the location of the lesion. Those with cysticerci in the sellar region may have vision and hormonal issues. In the eyes, cysticerci are usually found in the subretinal space, causing a gradual reduction in visual acuity or visual field abnormalities. The cysts can cause inflammation of the vitreous membrane, uveitis, and endophthalmitis, which is the most serious complication of ocular cysticercosis and can result in eye shrinkage. Cysticercal infection in striated muscles can cause weakening and enlargement over time.
Causes and mechanism Taenia solium, otherwise known as "the pork tapeworm", is a tapeworm in the Cestoda class and is a species of the genus Taenia. Taenia solium is a unique tapeworm because it can infect humans in two ways: as a definitive host (where the adult worm lives in the intestines, known as taeniasis) and as an intermediate host (where the larvae develop in tissues, known as cysticercosis).
The normal life cycle of Taenia solium involves humans as the definitive host and pigs as the intermediate host. The adult worm lives in the human small intestine and can grow up to 10 meters, though most reach 2–3 meters. Its head (scolex) is small (about 1 mm), round, and has 22–32 hooks arranged in two rows. Since pigs eat feces, the eggs remain in waste, increasing the chance of transmission.
In geographical areas where Taenia solium is common, poor sanitation and free-roaming pigs make it easy for pigs to consume human feces or contaminated food scraps. Once a tapeworm egg enters a pig's intestine, it hatches into a larva called an oncosphere. This larva penetrates the intestinal wall, enters the bloodstream, and travels through the body until it settles in a tissue site. There, it develops into a cysticercus—a fluid-filled sac containing an immature tapeworm head (protoscolex). When a human eats undercooked infected pork, the protoscolex attaches to the intestine and matures into an adult worm.
The life cycle of Taenia solium is completed when humans eat raw or undercooked pork containing mature cysticerci. However, humans more commonly become infected by ingesting tapeworm eggs through contaminated food or water. When Taenia solium larvae is ingested, the larvae hatches in the intestines and the oncospheres penetrate the intestinal mucosa before migrating to other parts of the body such as the CNS where they develop into vesicular (viable) cysticerci. Since Taenia solium proglottids are not motile and may break apart before being passed, infected feces can contain a high concentration of eggs. Contact with such feces can lead to infection with multiple cysticerci. These cysts take about three months to mature, and their effects depend on their number and location in the body.
As the immune system responds to cysticerci in the brain, cysticerci go through three different stages; first becoming inflamed (colloidal stage), then breaking down (granular stage), and finally turning into hardened nodules (calcified stage). Some cysticerci remain in the viable stage for years. During the colloidal stage, the inflammation can cause damage to the brain tissue, swelling, scarring, and damage to nerve cells. In the later granular and calcified stages, swelling decreases, however scarring and clusters of immune cells in the brain (brain granulomas) may remain.
Diagnosis Diagnosing neurocysticercosis can be challenging, especially in resource-limited areas, as available methods are often unreliable or inaccessible. Physical examination and laboratory testing are often not helpful in diagnosing neurocysticercosis. Diagnosis mainly relies on neuroimaging and blood tests. Diagnostic criteria were created by Del Brutto et al to help with the diagnostic process. When diagnosing neurocysticercosis, physicians may ask the affected individual about a potential history of exposure, such as contact with others who are infected with Taenia solium, or time spent in an area where Taenia solium is endemic.
Immunodiagnosis