Seizures are the most common clinical manifestation of parenchymal brain cysticercosis and usually represent the primary or sole manifestation of this form of the disease (Del Brutto et al. 1992). While seizure prevalence among patients with neurocysticercosis varies according to the population studied and the diagnostic methods used, most series have shown that seizures occur in up to 80 % of cases (Ndimubanzi et al. 2010).

Epileptogenesis in neurocysticercosis has been a subject of debate. It was initially believed that neurocysticercosis-related seizures occurred almost exclusively when parasites began to degenerate and that the pathological substract explaining the occurrence of the seizure disorder was the acute inflammation surrounding dying cysticerci. Further studies, however, showed that seizures may occur at any stage of cysticerci involution within the brain parenchyma, from viable cysts to calcifications. In the latter, the intense gliosis that develops around dying or already dead cysticerci, as well as periodic morphological remodeling of calcification with exposure of antigenic material to the brain parenchyma, or even the development of hippocampal sclerosis may be the factors accounting for the epileptogenic activity of calcified cysticerci (Gupta et al. 2012; Nash et al. 2004; Rathore and Radhakrishnan 2012; Rathore et al. 2012).

Neurocysticercosis is a major cause of acquired epilepsy in most of the developing world and has been considered as the single cause explaining the increased incidence and prevalence of epilepsy in these regions (Blocher et al. 2011; Carabin et al. 2011; Del Brutto et al. 2005; Medina et al. 2005; Preux and Druet-Cabanac 2005; Villarán et al. 2009). In addition, this parasitic disease has also been considered one of the leading cause of adult-onset epilepsy (seizures starting in individuals aged 25 years or more) in areas of the world where the disease is endemic, particularly in developing countries of Latin America, Asia, and Africa. By the end of the twentieth century, large series of patients with adult-onset epilepsy from Brazil (Arruda 1991), Ecuador (Del Brutto and Noboa 1991), Mexico (Medina et al. 1990), India (Chopra et al. 1981), and South Africa (van As and Joubert 1991) demonstrated that neurocysticercosis occurred in 25–50 % of the cases, representing the single most common cause of this syndrome. On the other hand, there is more recent evidence suggesting that neurocysticercosis may no longer be the most common cause of symptomatic adult-onset epilepsy in patients evaluated in, at least, some urban centers of disease-endemic countries (Del Brutto and Del Brutto 2012a; Suástegui et al. 2009). In such regions, neurocysticercosis is now outnumbered by cerebrovascular diseases and brain tumors which appear to be the leading causes of acquired epilepsy in adult populations. Two factors may be responsible for the reported drop in the number of patients with neurocysticercosis-related adult-onset epilepsy, including increased sanitation and widespread availability of neuroimaging machines which allow early recognition of neurocysticercosis cases by general practitioners who can start prompt cysticidal drug therapy, avoiding long-term sequelae of chronically untreated disease such as poor seizure control.

Seizures due to neurocysticercosis are most often generalized tonic-clonic or simple partial with motor symptomatology, although some patients may present with complex partial seizures, myoclonic seizures, truncal seizures, or even with specific epileptic syndromes such as the Landau-Kleffner syndrome. The type of seizures has been considered to be related to the number and topographic location of the parasites, whereby patients with a single lesion present with partial seizures, while patients with multiple lesions have tonic-clonic generalized seizures (Sotelo et al. 1985). However, a study of 203 patients with epilepsy due to neurocysticercosis showed no difference in the frequency of partial seizures in patients with single parenchymal brain cysts as compared with those with multiple cysts (Del Brutto et al. 1992).

From 5 to 15 % of patients with parenchymal brain cysticercosis present focal signs in the neurological examination (Carabin et al. 2011). While weakness associated with pyramidal tract signs predominate, almost every focal neurological sign has been described in these patients, including sensory deficits, language disturbances, involuntary movements (hemichorea, tremor, facial myokymia, and blepharospasm), parkinsonian rigidity, gait disturbances, and signs of brainstem dysfunction (Keane 1982; McCormick 1985; Sotelo et al. 1985). As expected, focal signs are related to parasites strategically located in eloquent areas of the brain parenchyma, particularly in the cerebral cortex or the brainstem (Del Brutto and Del Brutto 2013a). Interestingly, parasites located in the basal ganglia are most often clinically silent (Cosentino et al. 2002). Focal neurological deficits in patients with parenchymal brain cysticercosis usually follow a subacute or chronic course resembling that of a brain tumor or focal granulomatous process such as an intracranial tuberculoma. However, some patients present with a stroke-like onset and rapid development of focal signs resembling a cerebrovascular event (Del Brutto 2012).

Different pathogenetic mechanisms explain the occurrence of increased intracranial pressure in patients with parenchymal neurocysticercosis, the most common being the so-called cysticercotic encephalitis (Rangel et al. 1987). This severe form of the disease most often affects children and young women and results from the acute inflammatory response that ensues in some patients as the result of massive cysticercal infection of the brain parenchyma. Intracranial hypertension in these cases is related to diffuse brain edema and not due to the physical presence of the parasites, since massive cysticercal infection of the brain parenchyma is not associated with increased intracranial pressure in the absence of immune reaction against the parasites (Del Brutto and Campos 2012). Patients with cysticercotic encephalitis present with a syndrome of acute or subacute onset characterized by clouding of consciousness, seizures, decreased visual acuity, headache, vomiting, and papilledema. These patients are severely ill during the acute phase of the disease (some patients may die as the result of intracranial hypertension), but those who survive the acute episode usually recover without sequelae (Noboa 1992).

Other mechanisms explaining the development of intracranial hypertension in patients with parenchymal brain cysticercosis include the rare presence of a large parenchymal brain cyst that displaces midline structures or the obstruction of CSF circulation due to a midbrain cyst that obliterates the cerebral aqueduct (Poon et al. 1980).

That patients with neurocysticercosis may develop psychiatric manifestations or organic mental disorders has long been known. Of historical importance, the first case of neurocysticercosis reported from Asia came from a man who had lived in a lunatic asylum in Madras (Wadia 1995), and it was not uncommon in Mexico City to find patients who, after being admitted to psychiatric hospitals for years, had a correct diagnosis of neurocysticercosis when they developed seizures or focal neurological signs (Nieto 1956).

The spectrum of cognitive impairment in patients with neurocysticercosis is wide and their prevalence has varied from one series to another. Recent studies have shown that a sizable proportion of these patients have a decrease in quality of life, depression, or mild cognitive impairment that is not directly related to the severity or the specific form of the disease (Bhattarai et al. 2011; de Andrade et al. 2010; Monteiro de Almeida and Gurjão 2011; Wallin et al. 2012). This contrasts with previous studies suggesting that these manifestations correlate with the presence of increased intracranial pressure but not with parenchymal brain cysts or with the coexistence of seizures (Forlenza et al. 1997). Overt dementia has been found in 6–15 % of neurocysticercosis patients, a finding that seems to be related with the presence of active disease (Ramirez-Bermudez et al. 2005; Rodrigues et al. 2012).

Psychotic episodes characterized by confusion, paranoid ideation, psychomotor agitation, violent behavior, and visual hallucinations have also been described in patients with parenchymal neurocysticercosis (Shandera et al. 1994; Shriqui and Milette 1992). Some of these episodes could represent attacks of psychomotor epilepsy or postictal psychosis (Feinstein et al. 1990).

The occurrence of headache without any other evidence of increased intracranial pressure has been reported in several series of neurocysticercosis patients with a prevalence that may be as high as 30 % of cases (Carabin et al. 2011). Such headaches are intermittent and resemble those seen in migraine, tension-type headache, or other primary headache disorders, raising the question of whether they are related to cysticercosis or may occur as an incidental finding in areas where both conditions are highly prevalent (Finsterer et al. 2006; Mishra 2007; Rajshekhar 2000). An old case-control study suggested that the prevalence of migraine-type headaches was significantly increased among patients with neurocysticercosis (Cruz et al. 1995). However, until recently, there was no convincing evidence of a cause-and-effect relationship between these two conditions. A large, case-control study comparing the prevalence of neurocysticercosis among patients with major neurological disorders found a significantly increased prevalence of parenchymal brain calcifications among patients with an otherwise typical “primary headache disorder” when compared with that seen in other neurological disorders (Del Brutto and Del Brutto 2012b). It is possible that periodic remodeling of intracranial calcifications exposing parasitic antigenic material to the host causes transient inflammatory changes in the brain parenchyma that may be the cause of transient and recurrent headache episodes mimicking a primary headache disorder, thus providing a rationale for the association between headache and calcified neurocysticercosis.

Communicating hydrocephalus is the most common pathogenetic mechanism explaining the occurrence of increased intracranial pressure in patients with subarachnoid neurocysticercosis. Hydrocephalus may occur by extension of the subarachnoid inflammatory reaction to the leptomeninges at the base of the brain occluding the foramina of Luschka and Magendie or by chronic inflammation and fibrosis of the arachnoid villi causing obstruction to the reabsorption of CSF (Lobato et al. 1981). In these patients, the syndrome of increased intracranial pressure without focalizing signs presents with a subacute onset and progressive course, although some patients may follow a chronic and normotensive course (Revuelta-Gutierrez and Valdéz-García 1995). Hydrocephalus is an ominous sign associated with a 50 % mortality rate at 2 years (Sotelo and Marin 1987).

Development of large cysts at the Sylvian fissure or CSF cisterns at the base of the brain (particularly the cerebellopontine angle cistern) are often associated with focal neurological deficits and signs and symptoms of increased intracranial pressure of subacute onset and progressive course that resemble the clinical manifestations of intracranial tumors or other focal granulomatous infections of the central nervous system (Fleury et al. 2011; Kelesidis and Tsiodras 2012).

Cysticercotic arachnoiditis causes entrapment of cranial nerves arising from the ventral aspect of the brainstem. The oculomotor nerves, running a long course within the basal subarachnoid space from their origin until their entrance into the cavernous sinuses, are often enclosed within the dense inflammatory exudate that occurs in this form of the disease. Extraocular muscle paralysis, diplopia, and pupillary abnormalities are the result of this entrapment (Keane 1993). The optic nerves and the optic chiasm may also be encased within this exudate with the subsequent development of diminution of the visual acuity or visual field defects (Keane 1982).

The absence of fever and signs of meningeal irritation have been considered useful for the differential diagnosis between cysticercosis and other causes of meningitis such as that caused by pyogenic microorganisms, Mycobacterium tuberculosis or fungi. However, the clinical course of some patients with cysticercotic meningitis is acute and may be associated with fever and neck stiffness. So, this parasitic disease should also be included in the differential diagnosis of acute meningitis in endemic regions (Bonametti et al. 1994; Srinivas and Chandramukhi 1992).

A stroke may occur in up to 12 % of patients with neurocysticercosis, particularly in those with the subarachnoid form of the disease (Marquez and Arauz 2012). It must be noted, however, that in endemic regions, a patient with neurocysticercosis may have a stroke from unrelated reasons. Therefore, the diagnosis of neurocysticercosis-related stroke is only possible after proper interpretation of data provided by neuroimaging studies, results of immunologic tests, CSF findings, and the evaluation of other risk factors for cerebrovascular disease that may be present in a given patient (Del Brutto 1992).

A variety of stroke syndromes, including transient ischemic attacks, cerebral infarctions, and intracranial hemorrhages, have been described in patients with neurocysticercosis (Table 7.1). Different stroke subtypes are related to different pathogenetic mechanisms and produce varied clinical manifestations (Cantú and Barinagarrementeria 1996). Transient ischemic attacks have been occasionally reported and are most often related to intermittent stenosis of major intracranial arteries secondary to meningeal cysticerci engulfing such vessels. A sizable proportion of these patients eventually develop a cerebral infarction when the inflammatory process occludes the affected artery (Aditya et al. 2004; McCormick et al. 1983).

Cerebral infarctions occur as the result of inflammatory occlusion of small penetrating branches of major intracranial arteries or of occlusion of major vessels. Small infarctions may be located in the subcortical white matter, the internal capsule, or the brainstem and present as lacunar syndromes (ataxic hemiparesis, pure motor hemiparesis, sensorimotor stroke) indistinguishable from those caused by atherosclerosis (Barinagarrementeria and Del Brutto 1989). Large cerebral infarctions, related to the occlusion of the anterior or middle cerebral artery, cause focal neurological signs that may be associated with cognitive decline when both anterior cerebral arteries are affected (Monteiro et al. 1994; Rodriguez-Carbajal et al. 1989).

Hemorrhagic strokes have been reported in a dozen of patients with neurocysticercosis (Viola et al. 2011). Some of them have had subarachnoid hemorrhages related to the rupture of an inflammatory (mycotic) aneurysm induced by the inflammatory reaction that often surrounds subarachnoid cysticerci (Huang et al. 2000; Kim et al. 2005; Soto-Hernández et al. 1996). Some other patients have developed parenchymal brain hemorrhages that have been thought to be related to the damage of a small artery in the vicinity of a parenchymal brain cyst (Alarcón et al. 1992; Téllez-Zenteno et al. 2003).