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, and lymphadenopathy (especially of the occipital and cervical nodes) begins. Other clinical features may include splenomegaly, mononuclear leukocytosis, and hepatocellular dysfunction, rarely presenting with jaundice (33).
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 (03; 52). 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, which is an encephalopathy characterized by visual hallucinations and perceptual distortions of objects and body parts, also known as metamorphopsia (27). 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 (37).
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 (34). 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 T2 hyperintensities on MRI of cervical and thoracic spinal cord segments (42). Symptoms may include paresthesias, extremity weakness, and loss of sphincter control (31).
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). Brachial plexus neuropathy associated with infectious mononucleosis has also been reported (47).
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 (04).
A considerable amount of research has been conducted 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 (05; 44). It is also suggested that Epstein-Barr virus-related infectious mononucleosis is a greater risk for multiple sclerosis than asymptomatic Epstein-Barr virus infection (30).
There are multiple hypotheses on the mechanism of the pathogenesis of Epstein-Barr virus leading to multiple sclerosis. The first posits that Epstein-Barr virus antigens trigger cross-reactivity to CNS self-antigens by T-cells previously exposed to Epstein-Barr virus. This is further promoted by poor clearing of Epstein-Barr virus-infected B cells, prolonging CD8+ T-cell exposure to Epstein-Barr virus antigens (36). Another hypothesis states that multipel sclerosis is not primarily an autoimmune disease, but rather a disease that has secondary autoimmune reactions that cause bystander injury when the CNS is exposed to Epstein-Barr virus antigens--both latent antigens during latency and lytic antigens during viral replication--leading to the relapse symptoms (attacks) observed in multiple sclerosis. This is suggested by the presence of gadolinium-enhancing lesions on brain MRI scans in relapsing-remitting multiple sclerosis (02; 32). In this hypothesis, therefore, it is the clinical attacks in relapsing-remitting multiple sclerosis that are immune-driven when Epstein-Barr virus antigen-induced autoimmunity causes bystander injury in the CNS. A third hypothesis describes a “two-hit” scenario that allows inflammatory cells to migrate into the CNS in the presence of Epstein-Barr virus infection (19).
Despite the strong association between Epstein-Barr virus and multiple sclerosis occurrence, the etiology and pathogenesis of multiple sclerosis are complex and heterogenous and have yet to be fully understood; thus, the role of Epstein-Barr virus in its pathogenesis remains unclear (06). Little evidence yet exists to definitively prove any of the hypotheses above.
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 (29; 18).
Prognosis and complications
Epstein-Barr virus encephalitis is often self-limiting and is relatively benign compared to other herpes encephalitides (03). 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 (03). 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 the 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 6 months post-onset (14).