Presentation and course
Young children and young adults have a predilection for symptomatic infections, with severity ranging from mild to fulminant life-threatening complications. Infectious mononucleosis due to Epstein-Barr virus is one of the most common causes of prolonged illness in adolescents and young adults in Western societies. Infection is often spread by saliva in teens and young adults, designating infectious mononucleosis as the kissing disease. After an incubation period of 4 to 7 weeks, a typical triad of fever, pharyngitis, lymphadenopathy (especially of the occipital and cervical nodes) begins. Other clinical features may include splenomegaly, mononuclear leukocytosis, and hepatocellular dysfunction rarely presenting with jaundice (38).
Epstein-Barr virus has been associated with multiple neurologic complications including acute encephalitis, meningitis, acute cerebellar ataxia, myelitis, Guillain-Barré syndrome, cranial nerve palsies, neuropsychiatric syndromes, mononeuropathies, and acute disseminated encephalomyelitis (17; 49; 02). Meningitis and encephalitis are the most common complications of acute Epstein-Barr virus infection, with encephalitis being less frequent than meningitis. The initial symptoms of meningitis are severe headache and neck stiffness. Encephalitis may present with coma, seizures, delirium, or focal neurologic deficits before infectious mononucleosis is apparent. Epstein-Barr virus encephalitis may also present with ataxia due to cerebellitis (24) and is also associated with Alice in Wonderland syndrome (AIWS), which is an encephalopathy characterized by visual hallucinations and perceptual distortions of objects and body parts, also known as metamorphopsia (28). It remains the commonest infectious cause of Alice in Wonderland syndrome, and although the pathophysiology remains controversial, local cerebral edema and ischemia similar to that shown in migraine-associated Alice in Wonderland syndrome have been postulated (42). Findings from fMRI studies show that metamorphopsia is linked to functional impairment of the occipital cortex and over activation of specific parietal regions (07).
Acute disseminated encephalomyelitis is a post-infectious immune-mediated syndrome presenting with encephalopathy and focal neurologic deficits, with lesions often seen in both the brain and spinal cord. Epstein-Barr virus may be the antecedent infection, and diagnosis is based on a reactive Epstein-Barr virus IgM serology (37). Epstein-Barr virus may cause an acute myelitis, but this is more common in immunocompromised patients through local reactivation of the virus (52). It is an inflammatory myelopathy, with lymphocytic pleocytosis and elevated protein concentration in the CSF as well as abnormal hyperintensity on MRI of cervical and thoracic spinal cord segments (46). Symptoms may include paresthesias, extremity weakness, and loss of sphincter control (35).
Epstein-Barr virus infection has also been associated with peripheral nervous system syndromes, including cranial neuropathies and polyradiculopathies (11). Hottenrott described a case of Epstein-Barr virus causing a lumbosacral radiculitis with radicular pain in an immunocompetent patient (23). Mechanisms of brachial plexus neuropathy from Epstein-Barr virus include acute virus infection, which is often associated with lymphadenopathy, and a post-infectious brachial neuritis (14).
Guillain-Barré syndrome is associated with multiple antecedent infections, the most common being Campylobacter jejuni, cytomegalovirus, Epstein-Barr virus, and Mycoplasma pneumoniae. All four of these infections associated with Guillain-Barré syndrome cause the formation of antibodies that cross-react with glycoconjugate proteins on peripheral nerves. Epstein-Barr virus, cytomegalovirus, and Mycoplasma pneumoniae can also form cold agglutinins that bind to carbohydrate antigens on glycoconjugate proteins, which is a similar mechanism to how antibodies are produced to gangliosides (26). Miller Fisher syndrome, a variant of Guillain-Barré syndrome, can be precipitated by Epstein-Barr virus infection as shown in a case report of a 14-year-old boy with bilateral cranial nerve dysfunction, limb hyporeflexia, and positive anti-GQ1b antibodies (10). The pathophysiological mechanism of Epstein-Barr virus-induced Miller Fisher syndrome is likely similar to that of the cross-reactivity theory with Epstein-Barr virus and Guillain-Barré syndrome (03).
A considerable amount of research has been carried out to investigate the association between Epstein-Barr virus and multiple sclerosis; however, a causal relationship has not been definitively demonstrated. Seropositivity for Epstein-Barr virus is as high as 100% in some study cohorts of patients with multiple sclerosis, with lower rates being found in patients without multiple sclerosis of the same age range (01). Risk of multiple sclerosis following Epstein-Barr virus infection is suggested in a longitudinal analysis of a cohort of adults with multiple sclerosis (04; 47). There are multiple hypotheses on the mechanism of the pathogenesis of Epstein-Barr virus leading to multiple sclerosis. Penders hypothesis proposes that the virus infects forbidden memory B cells that are active against host CNS epitopes and rescues them from apoptosis, thereby allowing them to act as antigen-presenting cells that activate CD4+ T cells and lead to chronic inflammation (40; 30). Other hypotheses describe a two-hit scenario that allows inflammatory cells to migrate into the CNS in the presence of Epstein-Barr virus infection (19). However, most studies conducted to investigate this subject have failed to show the presence of Epstein-Barr virus within multiple sclerosis lesions, which has led to controversy about the theories and a persistent lack of evidence of causality (29; 15; 47). The etiology and pathogenesis of multiple sclerosis is complex and heterogenous, and it has yet to be fully understood; thus, the role of Epstein-Barr virus in its pathogenesis remains unclear (05).
Although subacute sclerosing panencephalitis is classically known as a consequence of measles infection, there have been a few cases reported that include Epstein-Barr virus as a factor. Hochberg and colleagues described a case of a 13-year-old girl who died of subacute sclerosing panencephalitis during an acute mononucleosis infection (22). Brain tissue staining showed both measles and Epstein-Barr virus antigenic material. One hypothesis is that decreased cellular immunity from acute mononucleosis may be responsible for activation of latent measles virus. Epstein-Barr virus has also been implicated in nasopharyngeal cancer (51) as well as primary CNS lymphomas in immunocompetent and immunocompromised patients (34; 18).
Prognosis and complications
Epstein-Barr virus encephalitis is often self-limiting and is relatively benign compared to other herpes encephalitides (02). Rarely, the clinical course is complicated by cerebral edema, which can cause raised intracranial pressure and death. In children, it can be associated with subsequent developmental delay, and some adults show persistence of neuropsychiatric disorders after resolution of the acute illness (02). Similarly, Epstein-Barr virus myelitis is often complicated by permanent sequelae, with limited resolution of limb paresis. The prognosis of primary CNS lymphoma associated with Epstein-Barr virus among people living with HIV improves with the use of effective antiretroviral therapy. The prognosis in immunocompetent patients depends on many factors, and predictive scores such as the International Extranodal Lymphoma Study Group (IELSG) score and Memorial Sloan Kettering Cancer Center (MSKCC) prognostic score can be used to stratify patients prognoses (18). Prognostic factors generally include the age of the patient (with older age being associated with poorer outcomes) and occurrence of adverse events associated with mass effect from the tumor itself.
Compared to other viruses such as hepatitis E virus, cytomegalovirus and Epstein-Barr virus cause milder forms of Guillain-Barré syndrome with better neurologic outcomes, and full recovery is usually around six months post-onset (13).