Presentation and course
The classical clinical features of this disorder are as follows (01):
| (1) Onset before 18 months of age; |
| (2) Recurrent attacks of hemiplegia involving either side of the body; |
| (3) Other paroxysmal episodes, including tonic spells, dystonia, chorea, nystagmus, dyspnea, and autonomic disturbances, occurring in association with the episodes of hemiplegia or independently; |
| (4) Episodes of bilateral hemiplegia either at the onset of the attack or as the attack shifts from one side of the body to the other; |
| (5) Resolution of the hemiplegia with the onset of sleep and prolonged episodes of recurrence 10 to 20 minutes after awakening; |
| (6) Evidence of developmental delay and other neurologic abnormalities such as choreoathetosis, dystonia, and ataxia. |
The presence of all of these criteria is not necessary to make the diagnosis in an otherwise typical case. Eighty-five percent of patients have paroxysmal eye movements within the first 3 months of life, which often herald the onset of symptoms. Thirty-two percent of patients had abnormal eye movements, often nystagmus, noted within 1 to 2 days of birth (37; 30). The patient may have episodes of head and eye deviation with ipsilateral limb extension associated with crying. Nystagmus and dyspnea may also occur. Hemiplegia of the affected side may follow. Consciousness is preserved. The duration of these attacks may vary from minutes to days. Hemiplegia is aborted with sleep but may recur on awakening. Episodes of quadriparesis may occur. The patients are usually flaccid unless there is superimposed dystonia. Episodes of dystonia, nystagmus, dyspnea, and autonomic symptoms, such as flushing or pallor, may occur independently of hemiplegic episodes. Some children may develop normally initially; however, developmental delay is usual. Chronic ataxia and choreoathetotic movements may develop during the course of the disorder and remain (22; 44).
According to a published series of 44 patients (16), the course of the disorder appears to consist of 3 phases. The first phase, lasting about 1 year, is characterized by mild developmental delay, intermittent nystagmus or eye deviation, and dystonic episodes. During the second phase, evolving over 1 to 5 years, patients experience episodes of hemiplegia and quadriplegia, lose developmental milestones, and begin to exhibit fixed neurologic deficits, choreoathetosis, and ataxia. During the third phase, patients continue to have episodes of hemiplegia, although at a lesser frequency, and neurologic deterioration plateaus. Earlier onset of the disorder appears to portend a poorer neurologic prognosis. A few patients, typically those with later onset or fewer spells, may maintain normal or near-normal intellect.
A study of 187 patients in the United States AHCF Registry (45) demonstrated a mean age of onset of paroxysmal symptoms of between 1.9 and 12.2 months of age, depending on the causative mutation involved. Between 50% and 80% of patients develop epilepsy, and most have developmental delay and cognitive impairment of variable severity, and genotype-phenotype correlations are relevant to these manifestations as well, although they are not reliable enough to provide prognostic information for the individual patient or family (18; 45).
In view of the genotypic and phenotypic heterogeneity of children with alternating hemiplegia of childhood, Mikati and colleagues have proposed assigning the diagnosis to children who manifest both of the essential criteria, plus either 3 major or 2 major and 3 minor criteria, as defined below (17):
| (1) Essential criteria |
| | (a) Paroxysmal episodes of hemiplegia that alternate between the 2 sides and/or of quadriplegia |
| | (b) Evidence of abnormal baseline neurologic development |
| (2) Major criteria |
| | (a) Onset before 18 months of age |
| | (b) Episodes of dystonia |
| | (c) Different types of episodes occur independently or together at the same time with evolution from 1 or more symptoms to others during that 1 episode |
| | (d) Paroxysmal episodes of abnormal eye movements such as nystagmus and especially monocular nystagmus |
| | (e) ATP1A3 mutation |
| | (f) Plegic spells improve with sleep |
| (3) Minor criteria |
| | (a) Epileptic spells alone or in combination with nonepileptic spells |
| | (b) Nonepileptic episodes of altered consciousness alone or in combination with other spells |
| | (c) Abnormal tone and/or motor function, often including coexistent hypotonia and dystonia, ataxia, choreoathetosis, and poor oral motor control |
| | (d) Episodes of autonomic dysfunction |
Diagnostic workup at onset, including brain imaging, routine EEG, serum amino acid studies, urine organic acid assays, mitochondrial studies, and muscle biopsy, is normal. Ictal EEG can be normal as well (37).
Prognosis and complications
In typical cases of alternating hemiplegia of childhood with early childhood onset, motor and cognitive disability occurs. Many patients with this disorder develop intellectual impairment, spasticity, seizures, ataxia, and choreoathetosis. Developmental delay is a variable feature at onset. In a series of 9 patients, seizures typically developed after 2 years of age (31). The occurrence of status epilepticus correlated with poorer neurologic outcome. Patients in this group frequently show cerebellar atrophy and high signal in the hippocampus on MRI over time. However, 1 comprehensive longitudinal study of 157 patients with a mean onset of symptoms of 3.5 months showed no progression of clinical manifestations over up to 52 years. Most of the data for this study were collected retrospectively, but all patients were followed prospectively for 2 years. In addition, in this study, no statistically significant correlation between a history of severe paroxysmal hemiplegic/dystonic episodes and a worse neurologic outcome was identified (20). A longitudinal study underscores the progressive potential of this disorder in some patients (26).
Premature mortality has been described in patients with alternating hemiplegia of childhood and is unexplained by seizures or neurologic dysfunction alone. A study of 52 DNA-confirmed cases of alternating hemiplegia of childhood and 52 disease controls with epilepsy suggested that electrocardiographic abnormalities are more common in patients with alternating hemiplegia than in control patients with epilepsy, and have characteristics reflecting those of inherited cardiac channelopathies and most likely relate to impaired repolarization reserve (08).
Clinical vignette
A family was described by Rodriguez-Quiroga and colleagues and the vignette below is derived from this description (29).
A 19-year-old man first came to medical attention with anarthria, mild dysphagia, hypotonia, and severe bradykinesia involving all 4 limbs, and affecting face greater than arms and greater than legs. Tremor and stooped posture, frequently seen in Parkinson disease, were notably absent. Twelve other family members were interviewed and examined and the family was found to include individuals with episodic hemiplegia, epilepsy, mild cognitive impairment, developmental delay, dystonia, parkinsonism, and/or bulbar dysfunction. The pedigree of all neurologic dysfunction in this family was consistent with an autosomal dominant inheritance pattern. The affected family members were found to have a novel missense mutation in the gene ATP1A3.