From the Gülhane Military Medical Academy, Department of Pediatrics (VO, STY, RA) and Ophthalmology (FMM), Ankara, Turkey. Originally submitted June 14, 2006. Accepted for publication February 6, 2007.
The authors have no financial or proprietary interest in the materials presented herein.
Address correspondence to Vedat Okutan, MD, Gülhane Military Medical Academy, Department of Pediatrics, Ankara 06018, Turkey.
Benign sixth nerve palsy in children is commonly attributed to a preceding viral infection without definite proof.1 It can be an alarming sign, indicating the presence of significant underlying etiology. Rarely, abducens nerve palsy is recurrent and no underlying cause is found, so the diagnosis of benign recurrent abducens nerve palsy can be made.2 We describe a patient with benign recurrent abducens nerve palsy. To our knowledge, this is the first Turkish patient reported.
A healthy 11-month-old girl without a history of any medical problem presented to the pediatric department with an acute-onset esotropia in the left eye due to sixth nerve palsy. Esotropia increased with horizontal gaze to the left (in gaze toward the affected eye) (Fig. 1). There was also a severe face turn toward the left side. Fixation of colored objects was normal for both eyes. Her developmental milestones and vaccination history were normal for her age. Physical examination was unremarkable except for abducens palsy. All other cranial and peripheral nerves were intact, including corneal sensation. Pupillary light reactions were normal in both eyes. There was no evidence of nystagmus, and dilated funduscopy was unremarkable with no evidence of papilledema. A magnetic resonance imaging scan of the brain disclosed no tumor and no sign of increased intracranial pressure; the cavernous sinuses and the brainstem appeared normal. Part-time occlusion therapy was ordered for the right eye and the palsy resolved during a period of 2 months.
Figure 1. Esotropia in Primary Position, Which Increases in the Field of Action of the Paretic Lateral Rectus Muscle of the Left Eye. Ocular Version Testing Revealed an Inability to Abduct the Left Eye past the Midline. Pupils Were Dilated for Fundus Examination.
Six months later, she returned to the department with a further episode of sixth nerve palsy in the left eye during a mild upper respiratory tract infection. Direct and consensual pupillary reactions to light were normal in both eyes. There was no nystagmus. Dilated funduscopy was normal with no evidence of papilledema. Once again, medical and neurological history and examination were unremarkable. Serological studies were negative for Mycoplasma pneumoniae, Epstein–Barr virus, cytomegalovirus, and Toxoplasma gondii. Her AchR Ab levels were negative. No beta-hemolytic streptococci were isolated in her throat culture. A repeat magnetic resonance imaging scan of the brain was normal.
A diagnosis of benign recurrent sixth nerve palsy was made and part-time occlusion therapy was ordered for the right eye. The palsy partially recovered with a mild abduction deficit in the left eye and mild face turn to the left during the next 2 months (Fig. 2). After regular follow-up for 18 months, there was no recurrence of palsy or any other neurologic deficit.
Figure 2. Esotropia in Primary Position and Mild Abduction Deficit on Left Gaze.
Isolated unilateral sixth nerve palsy in children can be associated with different clinical pictures. The palsy may be due to a post-infectious process; Epstein–Barr virus and cytomegalovirus have been documented etiologies. Other uncommon etiologies include Mycoplasma pneumoniae infection, Chlamydia pneumoniae infection, and Lyme disease.1,3,4 Benign recurrent abducens nerve palsy is a rare condition of unknown etiology. There are only 23 cases in childhood reported in the literature. Most of these cases seem to have followed an immunization or febrile illness.2 The recurrences of palsy in this group of patients has not been associated with any identifiable intracranial process. Multiple recurrences in the absence of any recognizable febrile illness clearly suggests that not all “benign” sixth nerve palsies in children are due to post-infectious processes.5 Hypotheses include neurovascular compression by aberrant artery and migraine.6
The diagnosis can be made in the presence of a healthy optic disc and in the absence of any other cranial nerve involvement. All other causes of abducens nerve palsy should be excluded and there should be no evidence of concurrent illness or history of precipitating events.1
The left side is more commonly affected and the majority of patients are female, as with our patient. Similar to our patient, ipsilateral recurrences were a prominent feature and the onset is painless.2,5 No systemic or neurologic sequelae are reported and, in the majority of patients, spontaneous full recovery in 6 months has been observed. Our patient recovered within 2 months. The average interval between recurrences is reported to be 1.3 years.5 In our patient, the interval between attacks was significantly shorter at approximately 6 months.
With recovery from the initial episode, the abducens nerve may have become predisposed to recurrent inflammatory episodes and recurrent loss of function. Most often, these recurrences are triggered by febrile illnesses of childhood.7 In our patient, recurrence was concurrent with a febrile illness probably caused by a viral etiology.
The diagnosis of “benign” sixth nerve palsy should only be made once other causes of abducens nerve palsy are excluded. The most common and serious cause is intracranial neoplasia, which often presents with papilledema, nystagmus, and other cranial nerve abnormalities.5 Magnetic resonance imaging is useful for diagnosing intracranial pathologies. Bendszus et al.8 reported a series of 43 patients with isolated, acute, unilateral sixth nerve palsy in which initial magnetic resonance imaging revealed no lesion in 37% of patients. Tumors not found on initial magnetic resonance imaging have been found up to 1 year later, and it has been reported that some cases with chronic, benign abducens palsies later turned out to be caused by various serious pathologies such as neoplasms or aneurysms.9,10 For all of the reasons mentioned, it seems appropriate to repeat magnetic resonance imaging routinely in patients presenting with an acute sixth nerve palsy, especially with recurrence or any other neurologic sign. Head trauma, infections such as meningitis, Lyme disease, and Gradenigo’s syndrome are also other common causes.11,12
Treatment of acute sixth nerve palsy in children is mainly aimed at preventing amblyopia and preserving binocular fusion. Diplopia may be a prominent symptom during the acute phase in all cases with sixth nerve palsy, but children may rapidly learn to suppress the second image of the deviating eye, which can result in amblyopia. Because strabismic amblyopia may develop prior to resolution, we only instituted part-time occlusion therapy for our case, in the amblyogenic age range. Occlusion may also prevent secondary contracture of the medial rectus muscle of the deviating eye. Face turn, which was significant at the first attack in our case, is beneficial in maintaining binocular vision, and parents should permit their children to assume the anomalous head posture. However, parents or pediatricians should be aware of the head posture of their child or patient, which may be a sign of various extraocular muscle palsies. If a child is not recovering sixth nerve function, chemodenervation of the antagonist medial rectus muscle may help to rapidly restore binocularity.13 At least 6 months after the onset of an acute sixth nerve palsy, the chance for spontaneous recovery is greatly reduced and surgery can be considered.14
Benign recurrent abducens nerve palsy is a rare clinical entity, but it should be included in the differential diagnosis of sixth nerve palsy in the absence of obvious underlying pathology.
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- Currie J, Lubin JH, Lessell S. Chronic isolated abducens paresis from tumors at the base of the brain. Arch Neurol. 1983;40:226–229.
- Crompton JL, Keith CG. Giant intracavernous aneurysm: rare cause of isolated sixth cranial nerve palsy in a child. Med J Aust. 1976;2:342–343.
- Villa G, Lattere M, Rossi A, Di Pietro P. Acute onset of abducens nerve palsy in a child with prior history of otitis media: a misleading sign of Gradenigo syndrome. Brain Dev. 2005;27:155–159. doi:10.1016/j.braindev.2004.02.003 [CrossRef]
- Lesser RL, Kornmehl EW, Pachner AR, et al. Neuro-ophthalmologic manifestations of Lyme disease. Ophthalmology. 1990;97:699–706.
- Scott AB, Magoon EH, McNeer KW, Stager DR. Botulinum treatment of childhood strabismus. Ophthalmology. 1990;97:1434–1438.
- King AJ, Stacey E, Stephenson G, Trimble RB. Spontaneous recovery rates for unilateral sixth nerve palsies. Eye. 1995;9:476.