Isolated oculomotor nerve palsy revealing infectious mononucleosis.

Abstract

Epstein–Barr virus (EBV) is a member of the herpesvirus family causing infectious mononucleosis (IM). Neurological complications have been reported rarely. A previously healthy 18-year-old woman presented with a 5-day history of binocular vertical diplopia, asthenia and night sweats. Ophthalmological examination was normal. Pupils were equal and reactive to light, with no relative afferent pupillary defect. Oculomotor examination revealed a left pupil sparing partial third nerve palsy (partial ptosis and moderate restriction of elevation, depression and adduction). The rest of the neurological examination was unremarkable. General examination revealed an apyretic patient with painless disseminated lymph nodes and a mild hepatomegaly. Brain MRI showed a focal T2 abnormal hyperintense signal located on the left oculomotor nerve at its exit from the mesencephalon. A gadolinium enhancement was noted (Fig. 1). Biochemistry abnormalities showed hepatic cytolysis (ASAT/ALAT 3ULN) and C-reactive protein level of 13.5 mg/l. IgM and IgG antibodies against Epstein–Barr viral capsid antigen were found positive, whereas IgG antibodies for Epstein–Barr nuclear antigen were negative. Epstein–Barr viral load testing by PCR reached 65 000 copies/ml. This biological profile was indicative of an acute primary EBV infection. Diplopia gradually resolved in a few days, followed in several weeks by the resolution of asthenia and lymphadenopathy. At the 2-month follow-up visit, neuro-ophthalmological examination and liver enzymes level had return to normal. A new brain MRI showed the decrease in size of the previously noted hyperintense signal of the left oculomotor nerve, with mild residual gadolinium enhancement. Peripheral and/or central nervous system (CNS) involvement is rare in IM, occurring in <5% of the patients (Silverstein et al. 1972). The most frequent neurological disturbances observed in IM are meningitis and encephalitis. Other manifestations include cranial nerve palsy, peripheral mono- or polyneuropathies, transverse myelitis, optic neuritis, Guillain–Barré and Miller Fisher syndromes (Brazis & Miller 2005). Involvement of any cranial nerve has also been reported. Isolated or multiple cranial nerve involvement may occur, although mononeuritis seems to be the least common. In some patients, oculomotor nerve palsies occur in association with more spread CNS manifestations. In others, the paresis is isolated and may even be the presenting manifestation of EBV infection. Only four cases of isolated third nerve palsy (Erben et al. 2008), two of isolated fourth nerve palsy and three others of isolated bilateral sixth associated with IM have been published to date. Concerning the MRI findings, two previous cases of oculomotor nerve palsy in IM were reported with a very similar aspect on MRI (Erben et al. 2008). However this MRI appearance is non-specific. The differential diagnoses on MRI include Lyme neuroborreliosis, neurosyphilis, viral infection (HIV, VZV and CMV), tuberculosis, neurosarcoidosis, CNS lymphoma, vasculitis and Tolosa–Hunt syndrome. The pathogenic mechanism explaining how EBV infection can affect neurological structures remains unclear. The possibility of a direct viral invasion to neural tissues and/or of an indirect post-infectious immunological mediated mechanism is debated (Tselis 2014). The combination of both mechanisms is highly probable making the descriptive term ‘parainfectious’ the most appropriate (Tselis 2014). Concerning the treatment, the use of corticosteroids in patients with neurological manifestations related to IM remains controversial (Odumade et al. 2011). It has been argued that steroids may enhance replication of herpesviruses. However, corticosteroids may be beneficial in patients with impending airway obstruction and when severe neurological or haematological (thrombocytopenia and haemolytic anaemia) complications occur (Brazis & Miller 2005). It appears that in most of the cases, the prognosis is good with a spontaneous recovery of the cranial nerve palsy over weeks to months, only with supportive measures (Erben et al. 2008). Epstein–Barr virus infection should be considered when confronted to an oculomotor palsy, mainly when it occurs in adolescents or young adults. Usually, the prognosis is good.