Alternating hemiplegia of childhood (AHC) is a rare disorder that affects children in the first year of life. They experience spells of tonic spasm or hemiplegia of varying duration that will alternately affect one side of the body and then the other. Previous descriptions of concurrent eye movement abnormalities mention monocular pendular nystagmus (1), strabismus (1), and episodic eye deviations (2). This report helps to clarify the ocular motor disorder accompanying AHC.
A 14-month-old boy was reported by his parents to have developed a 30-minute spell of OS abduction with posturing of the left arm at 7 days of age. The next spell occurred several days later, manifested by OD abduction and right arm posturing. The ocular motor spells subsequently alternated from one eye to the other with varying frequency. Occasionally, the boy would have several spells a day, but could be free of them for over 2 weeks. At 8 months of age, he began developing concurrent ipsilateral hemiplegia instead of tonic posturing during the spells of eye abduction. The hemiplegia was most dramatic during right eye spells. Spells aborted with sleep but otherwise lasted minutes to hours. Consciousness was unaffected, and he occasionally became hypotonic prior to spells. Flunarizine did not alter the duration or severity of spells, but he obtained some relief with high doses of phenobarbital.
He was born at 39 weeks gestation by cesarean section due to failure to progress and was hypotonic following delivery. He was not ambulatory at the time of examination (age 14 months). His interictal neuro-ophthalmologic examination at 14 months of age was normal apart from mild generalized hypotonia. Review of a videotaped spell at 18 days of age showed repetitive abducting jerks of the OS at a frequency of about 1 Hz (Fig. 1). The OD remained stationary in primary position and at times appeared to be tonically abducted a few degrees. The left arm was held in a raised and flexed position. Interspersed throughout the prolonged spell were several 3-second to 5-second bursts of very rapid upbeat nystagmus.
A second videotaped spell at 1 year of age disclosed abducting jerks of the OD at a frequency of about 1 Hz (Fig. 2A). There was no tonic deviation of the OS or upbeat nystagmus. During the period of repeated OD abduction jerks, the right arm was flaccid (Fig. 2B).
Magnetic resonance imaging of brain, computed tomography of chest and abdomen, cerebrospinal fluid, urine amino acids, and urine organic acids were normal. No mitochondrial genetic defects were identified. Electroencephalography (EEG) telemetry monitoring for 3 days revealed generalized slowing, but no spells occurred during that period.
At 2 10/12 years of age, he continues to have 10 attacks of isolated hemiplegia per month and four attacks of hemiplegia combined with monocular eye deviation and nystagmus per month, despite a prophylactic daily regimen of 5 mg flunarizine and 75 mg phenobarbital. If given promptly at attack onset, diazepam 1.5 mg orally or 2.5 mg rectally aborts the manifestations. The hemiplegia sometimes progresses to involve the opposite side of the body, leading to an asymmetric quadriparesis. Interictal periods last hours to days. He knows six sign language words and is still nonverbal and nonambulatory.
Alternating hemiplegia of childhood is characterized by paroxysmal spastic or dystonic attacks affecting one side of the body with onset prior to 4 months of age (1). Head deviations are uncommon. As the infant ages, the tonic attacks are often followed by hemiplegia. The prognosis for normal development is poor, and cognitive impairment becomes more apparent with age (3,4). Nearly all patients are developmentally delayed (5).
Hemiplegic attacks replace the tonic spasms as the predominant attack by 1 year of age. In one report (1), only one of 22 children was free of hemiplegic attacks by 1 year. Episodes of dystonic posturing may still appear within the spells of hemiplegia. Attacks last minutes to hours and may be bilateral. It is not uncommon for spells to be abolished by brief sleep. Paroxysmal autonomic phenomena, frequent early in the course of the illness, consist of focal blanching of a limb or whole side of the body (1). These autonomic phenomena often usher in the hemiplegic attacks. A family history of migraine is common.
Almost all children are hypotonic and ataxic and delayed in physical and mental development (1,3). Neuroimaging is routinely normal, and EEGs during spells rarely reveal epileptiform activity, although a number of patients later develop seizures (1,3).
In one report (1), episodic nystagmus was reported in 18 of 20 children; the nystagmus was monocular in 14, horizontal in 13, vertical in three, and not further described in the remaining two patients. The nystagmus typically alternates from eye to eye with each subsequent episode, as does the hemiplegia (1,6). Anisocoria occurs occasionally, the larger pupil contralateral to the abducting eye or gaze deviation (3,7). The nonabducting eye has been reported to have reduced horizontal but intact vertical movements during the spells. This patient demonstrated horizontal abduction jerks of one eye, but several jerks were accompanied by a tonic abducting deviation of the fellow eye. When vertical nystagmus was observed, it affected both eyes with very similar amplitudes. Apart from hypotonia, the monocular abduction jerks were the first manifestation noted by the parents.
The pathophysiology of the ocular motility dysfunction remains elusive. It is enticing to propose that epileptic activity from one cerebral hemisphere is responsible for tonic conjugate gaze deviations, but this proposition fails to explain the monocularity of the deviations. It seems more plausible that a pontine lesion causes the abduction jerks and inhibits the medial longitudinal fasciculus interneurons, preventing horizontal movement of the fellow eye.
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7. Fusco L, Vigevano F. Alternating hemiplegia of childhood: clinical findings during attacks. In Andermann F, Aicardi J, Vigevano F, eds. Alternating Hemiplegia of Childhood. New York: Raven Press, 1995:29–41.