Acquired sixth nerve palsies in children are rare and can be an indication of serious underlying pathology. A retrospective study1 of 253 children with sixth nerve palsy found that 40% had tumors, 10.2% had trauma, 11.1% had raised intracranial pressure, 6.2% had infection, 4.4% had vascular disease, and 4% had inflammatory disorders. In 13%, no cause could be found and they were diagnosed as having benign sixth nerve palsy. Another study2 of 132 children with sixth nerve palsy found that 10% had undetermined etiology (12.2% if congenital etiologies were disregarded). Benign sixth nerve palsy is diagnosed based on exclusion of all other serious causes, so a magnetic resonance imaging (MRI) scan, lumbar puncture, and full neurological examination should be performed.
A 6-month-old female infant presented with a 3-day history of limited abduction of her left eye and a head turn to the left. There was no family history of strabismus or other eye problems, and no vomiting, seizures, weakness, or neurological symptoms. She was born at 38 weeks by caesarean section and did not require any special care. Her immunizations were all up to date and there was no family history of any illness.
Examination revealed a head turn to the left greater for distance than near fixation. No deviation was found with the head posture, but a small left esotropia without it. She had complete (−4) restriction of abduction of the left eye, with no retraction or narrowing. There was no refractive error, and a normal fundus and media. Diagnosis of sudden onset left sixth nerve palsy was made and she was referred immediately to a pediatrician and admitted to the hospital.
Blood tests, a full neurological investigation including an urgent MRI scan, and lumbar puncture were all normal. She had no signs of fever or infection, was developmentally normal, and was therefore discharged home.
Ten days after onset, she was re-examined by a pediatrician and was well, although she had a brief but mild cough and cold, slight temperature, and lethargy since discharge.
Four weeks after onset, she had good equal vision, a slight head turn to the left, improved abduction (−1.5), and demonstrated binocularity. An ophthalmologist and pediatrician examined her and no additional problems were detected.
At subsequent regular visits, she maintained good binocularity, using a slight head turn and gradually recovered lateral rectus function that became full 5 months after onset (when she was 11 months old). She remained under ophthalmic and pediatric observation.
At 23 months of age (17 months after onset of the first palsy), she was referred with another sudden onset left sixth nerve palsy. She had equal vision, a moderate head turn to the left, and −4 limitation left abduction, but maintained binocular functions and stereoacuity with her head posture. She was admitted by a pediatrician. The neurological examination was repeated, including another MRI scan and lumbar puncture, with normal results.
One month after onset, she still had good equal vision, was binocular with a slight head turn, −1.5 limitation left abduction, and 110 seconds of arc using the Frisby test. Two months later, the limitation had resolved. At subsequent follow-up visits, movements remained full, with good equal vision and 55 seconds of arc.
At 2 years and 9 months of age, she presented with a third sudden onset sixth nerve palsy. She underwent extensive investigations again under a pediatric neurologist, including another MRI scan, lumbar puncture, and blood tests. Again, all of the tests were normal. She had good equal vision, a head turn to the left, and −4 limitation left abduction. She maintained good stereoacuity. No further ophthalmological problems were found.
Ten weeks after the third onset of lateral rectus palsy, her vision was good and equal, and she had a head posture only for distance targets, −1 limitation on left abduction, and 55 seconds of arc. Four months later, the palsy had completely resolved.
In this case, the child had three episodes of left lateral rectus palsy that improved on each occasion within 6 months. No other abnormalities were found despite extensive and invasive investigations on each occasion. There were no immunizations, infection, or febrile illness preceding the nerve palsies, although she had a mild cough and cold starting approximately 5 days after the initial sixth nerve palsy.
Benign sixth nerve palsies in children are reportedly painless and recover spontaneously.3–5 There is variation in the reported recovery time, probably due to the small numbers in each study, but the general consensus is that recovery will be within 6 months.1,3–5
Monitoring of the condition is important to detect changes, prevent development of abnormal binocular interactions, and maintain visual acuity. One study observing 12 individuals found 2 patients who developed concomitant esotropia and required strabismus surgery.3
Benign sixth nerve palsy may become recurrent in some patients. Yousef and Khan6 retrospectively reviewed 35 articles and found 54 non-recurrent and 41 recurrent cases (although these results may not be representative of the population due to a bias in reporting recurrent palsies rather than single episodes). Ipsilateral recurrence often occurs within a year of the initial event (73%) and subsequent recurrences rarely occur. Recurrences typically occurred in girls (P < .05), left eyes (P < .05), and children who first presented younger than 14 months. There were no recurrences in children who initially presented older than 12 years. Mahoney and Liu1 found 9 of 30 patients with benign sixth nerve palsies recurred; 3 of them had three episodes and 1 had four episodes. It has been suggested that individuals with an initial benign palsy may become predisposed to recurring inflammatory episodes with loss of function, possibly triggered by febrile illness.7 One case reported a child with eleven recurrences between 10 months and 11 years, although this appears to have been an exceptional case.8
The underlying pathological mechanism in benign sixth nerve palsy is unknown, although infection1,2,6,7,9,10 and various immunizations2,3,10–12 are most commonly linked. Other suggested mechanisms1 have been variant ophthalmoplegic migraine, atypical myasthenia gravis, inflammation secondary to viral infection, and neurovascular compression by an aberrant artery.4 It is difficult to establish a causative relationship between sixth nerve palsy and vaccine response or infection. Small children have frequent coughs and colds and it is difficult to know if this is a contributing factor or merely a coincidence.
Considering the possibility of recurrences, the level of investigation at each subsequent episode may need to be reviewed. The distress of the child and the family faced with repeated invasive procedures must be balanced against the risk of serious underlying etiology. It could be argued that after an initial benign episode, the probability of subsequent recurrences having serious etiology is markedly reduced. Long-term follow-up of these patients for a mean of 9 years uncovered no neurological problems or recurrences.3
- Mahoney NR, Liu GT. Benign recurrent sixth (abducens) nerve palsies in children. Arch Dis Child. 2009;94:394–396. doi:10.1136/adc.2008.142794 [CrossRef]
- Afifi AK, Bell WE, Menezes AH. Etiology of lateral rectus palsy in infancy and childhood. J Child Neurol. 1992;7:295–299. doi:10.1177/088307389200700310 [CrossRef]
- Sturm V, Schoffler C. Long term follow up of children with benign abducens nerve palsy. Eye. 2010;24:74–78. doi:10.1038/eye.2009.22 [CrossRef]
- Afifi AK, Bell WE, Bale JF, Thompson HS. Recurrent lateral rectus palsy in childhood. Pediatr Neurol. 1990;6:315–318. doi:10.1016/0887-8994(90)90023-T [CrossRef]
- Cohen HA, Nussonovitch M, Ashkenazi A, Straussberg R, Kaushansky A. Benign abducens nerve palsy of childhood. Pediatr Neurol. 1993;9:394–395. doi:10.1016/0887-8994(93)90110-X [CrossRef]
- Yousef SJ, Khan AO. Presenting features suggestive for later recurrence of idiopathic sixth nerve paresis in children. J AAPOS. 2007;11:452–455. doi:10.1016/j.jaapos.2007.02.013 [CrossRef]
- Bixeman WW, Von Noorden GK. Benign recurrent VI nerve palsy in childhood. J Pediatric Ophthalmol Strabismus. 1981;18:29–34.
- Sullivan SC. Benign recurrent isolated VI nerve palsy of childhood. Clin Pediatr (Phila). 1985;24:160–161. doi:10.1177/000992288502400311 [CrossRef]
- Vallee L, Guilbert F, Lemaitre JF, Nuyts JP. Benign paralysis of the 6th cranial nerve in childhood [article in French]. Ann Pediatr (Paris). 1990;37:303–305.
- Werner DB, Savino PJ, Schatz NJ. Benign recurrent sixth nerve palsies in childhood. Secondary to immunisation or viral illness. Arch Ophthalmol. 1983;101:607–608. doi:10.1001/archopht.1983.01040010607016 [CrossRef]
- Cheng DR, Crawford NW, Hayman M, Buckley C, Buttery JP. Recurrent 6th nerve palsy in a child following different attenuated vaccines: case report. BMC Infect Dis. 2012;12:105. doi:10.1186/1471-2334-12-105 [CrossRef]
- Kulkarni R, Kale K, Rathod A. Benign recurrent sixth nerve palsy in two children. Bombay Hospital Journal. 2011;53:638–639.