AHC is a rare neurological disorder in which repeated, transient attacks of hemiplegia (paralysis of a portion of the body, including the face) occur, usually affecting one side of the body or the other, or both sides of the body at once. It ranges from simple numbness in an extremity to full loss of feeling and movement. The attacks may last for minutes, hours or even days and are normally relieved by sleep. The attacks of hemiplegia typically alternate from one side of the body to another, but it is not uncommon for one side to be more frequently affected, or for episodes to begin on one side, and then switch to the other.
AHC episodes are often associated with triggers that precede or induce the attack. Triggers for AHC episodes may include–but are not limited to–environmental conditions (such as temperature extremes or odors), water exposure, physical activities (exercise, swinging), lights (sunlight, fluorescent bulbs), foods (chocolate, food dye), emotional response (anxiety, stress, fright), odors (foods, fragrances), fatigue, and medications.
The Symptoms of AHC:
Children with AHC exhibit a wide range of symptoms. These include tonic attacks (lack of muscle tone), dystonic posturing (stiffening of extremities), ataxia (lack of coordination when performing voluntary movements), nystagmus (fast uncontrollable movements of the eyes that may be side to side, up and down, or rotary) and other ocular motor abnormalities (eye disorders), developmental delays, and seizures.
Up to 50% of children with AHC develop “true seizures” sometime during the course of their illness.
The Diagnostic Criteria for AHC are as follows:
1.Onset of symptoms prior to 18 months of age
2. Repeated attacks of hemiplegia that alternate in laterality (meaning that the paralysis alternates from one side of the body to the other)
3. Episodes of bilateral hemiplegia or quadriplegia as generalization of a hemiplegic episode or bilateral from the beginning
4. Relief from symptoms upon sleeping, which may later resume after waking
5. Other paroxysmal disturbances, including tonic or dystonic spells, abnormal involuntary eye movements, or autonomic symptoms which may occur in addition to the hemiplegia attacks or independently
6. Evidence of developmental delay or neurologic findings such as choreoathetosis (a type of involuntary, continuous and flowing movement), dystonia or ataxia
The incidence of AHC is estimated at roughly 1 in 1,000,000 births, however, the true incidence may be higher since the disorder is commonly misdiagnosed due to the lack of awareness about AHC and the variability of its clinical features.
What are the long term effects of AHC?
Although the disorder is named of “childhood” those affected by AHC do not grow out of the disorder. The AHC episodes may change and sometimes even decrease in frequency as a child gets older.
Every child with AHC is unique, and children can be severely or mildly affected. However, as children get older, developmental problems between episodes became more apparent. These developmental problems may include difficulties in fine and gross motor function, cognitive function, speech and language and even social interactions. There is developing evidence that AHC may cause ongoing mental and neurological deficits with a progressive course. Early intervention for such children is extremely important to help maximize their developmental achievements.
Although there is no proof that the disorder limits life expectancy, these children do appear more susceptible to complications such as aspiration, which can sometimes be life-threatening. In rare cases, children have died suddenly and unexpectedly, in circumstances similar to the sudden death reported in patients with epilepsy (known as SUDEP, or sudden unexplained death in epilepsy). For this reason, careful evaluation to identify problems which could be associated with such episodes is a critical part of the care plan for these patients. Monitoring oxygen levels and insuring safe management of secretions may be needed during severe episodes.
Currently there is no cure for AHC but in 2012 the ATP1A3 gene was identified as a leading cause of AHC and represents approximately 76% of those affected. Ongoing research will hopefully provide a genetic identification for the remaining patients and a treatment for all. Presently, medicinal treatment options are extremely limited. The medication Flunarizine (trade name Sibelium), is a calcium channel blocker and has shown some effectiveness in reducing the severity, intensity and/or duration of paralytic episodes, but is not an effective treatment in all cases.