Alternating Hemiplegia Childhood (AHC) Disorder
Alternating Hemiplegia of Childhood (AHC) is a rare neurological disorder in which repeated, temporary attacks of paralysis occur, affecting one side of the body or the other, or even both sides at once. Complete paralysis of one side of the body is known as hemiplegia and paralysis of both sides at the same time is known as quadriplegia.
Attacks may range from mild weakness to full paralysis and may last for minutes, hours or even days. Typically, attacks alternate from one side of the body to the other, 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.
Children with AHC often have a wide range of other symptoms, including other types of abnormal movements. These include tonic attacks (stiffening of a limb), dystonic posturing (twisting postures), abnormal involuntary eye movements, developmental delays, fluctuating mental status and even true seizures.
Up to 50 percent of children with AHC develop "true seizures" sometime during the course of their illness. "True seizures" can be distinguished by characteristic findings on an EEG, and may be associated with tonic-clonic activity (repeated flexion and extension of limbs) and loss of consciousness, in contrast to other types of abnormal movements.
Episodes of tonic stiffening can sometimes represent seizure activity and sometimes not, so EEG testing is often necessary to determine what type of episode it represents.
"Autonomic" symptoms can also occur with episodes and consist of changes in the color or temperature of an involved limb.
Causes of AHC
The cause of AHC is still unknown. Most cases are sporadic, meaning that there is no family history of the disease. The chance of having additional children with AHC after having an affected child appears to be quite low (less than five percent). However, we suspect that AHC may have a genetic cause, as there are rare families who have more than one affected family member. These families are critical in helping researchers to identify a possible genetic cause for the disease. Males and females are equally affected.
Although the cause of AHC is unknown, a number of different triggers have been identified in association with episodes. Stress, infection and certain environmental triggers commonly trigger episodes in susceptible children. Common environmental triggers include exposure to bright lights, loud sounds, changes in temperature, excitement or other strong emotions, or bath or pool water. However, often attacks seem to occur without any trigger at all.
Other disorders can have similar symptoms as those seen in AHC. A careful clinical history, review of available video of episodes if possible, and specific testing (refer to section on how is AHC diagnosed) can help determine whether or not the disorder meets criteria for the diagnosis of AHC.
Diseases with Symptoms Similar to Those Seen in Alternating Hemiplegia of Childhood
- Migraine variants
- Familial hemiplegic migraine
- Basilar migraine
- Vascular disorders
- Arteriovenous malformations
- Stroke, emboli
- Moya moya syndrome
- Epilepsy syndromes
- Metabolic disorders
- Pyruvate dehydrogenase deficiency
- Mitochondrial encephalomyopathy with lactic acidosis and stroke-like episodes (MELAS)
- Neurotransmitter deficiency disorders
Long Term Effect of AHC
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. Early intervention for such children is extremely important to help maximize their developmental achievements.
Although the name "alternating hemiplegia of childhood" seems to imply that children could outgrow this problem, this is not the case although episodes frequently change and sometimes even decrease in frequency as a child gets older. While 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 addition, rare children have been reported to die 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 that could be associated with such episodes is a critical part of the care plan for these patients. For instance, some children may not be able to safely swallow during severe episodes, and an alternative feeding plan may be needed. Other children may breathe more shallowly during such episodes, resulting in need for monitoring of oxygen levels.
AHC is a "clinical" diagnosis, meaning that there isn't a specific blood test or imaging test that can definitely confirm a suspected diagnosis. The diagnosis of AHC is suspected if your child demonstrates a constellation of specific symptoms. Diagnostic tests that can help to confirm a diagnosis of AHC and exclude other disorders which mimic AHC include:
Certain tests need to be obtained to rule out causes of diseases that can present in a similar fashion to AHC, including lactate levels in blood, which might indicate a mitochondrial disorder such as MELAS or PDH deficiency, which can have episodes which are similar to those seen in AHC.
Studies of spinal fluid are often necessary to help exclude other causes of abnormal limb or eye movements, including neurotransmitter deficiency states, or to look for evidence of elevated lactic acid, as one might see in MELAS syndrome or other mitochondrial disorder.
Urine organic acid levels can sometimes help exclude other suspected metabolic disorders, which can cause similar symptoms.
A test that measures the electrical activity of the brain, an EEG can detect abnormal electrical activity and help make a diagnosis of epilepsy. Some children with AHC do have episodes with EEG abnormalities consistent with epilepsy. However, the majority of episodes they have are generally not associated with epileptiform activity. The presence of typical episodes like hemiparesis or abnormal eye movements that are not associated with epileptic activity can help to confirm a suspected diagnosis.
A small sample of the muscle is removed and examined to determine and confirm a diagnosis or condition other than AHC, such as a mitochondrial disorder.
MRI or imaging studies
Imaging studies of the brain or spine can help rule out other conditions, such as stroke.
There are, as of yet, no specific therapies that are uniformly effective in eliminating the episodes associated with AHC. Most doctors focus on trying to reduce or eliminate the abnormal movements, which are often so disabling in this disorder. Antiepileptic drugs are often used to try to reduce the frequency or severity of the movement disorder episodes, but are, unfortunately, rarely effective. However, in the child that also has "true seizures" in addition to other types of episodes, prevention of these episodes with antiepileptic medication is important, since prolonged seizure activity in these children can be associated with significant regression or loss of function.
Sleep can be helpful in shortening episodes, and sometimes physicians will prescribe medications to help induce sleep for this reason. These medications include chloral hydrate or benzodiazepines such as Valium or Midazolam. These latter drugs can work on both epileptic and non-epileptic events in some cases.
Proactive management strategies to optimize nutrition and physical well being are extremely important in maximizing developmental outcomes and improving quality of life. Learning disabilities should be identified and a specific treatment plan initiated as early as possible. Depression and behavioral problems also need to be addressed proactively, and, sometimes, specific medications directed to these problems can be helpful.
Following diagnosis in children with AHC, it is important that everyone on the care team work closely with parents in order to anticipate problems and pursue management aggressively to optimize outcomes. This is often extremely frustrating because attempts to limit episodes with medications often prove ineffective, and the associated side effects may worsen rather than improve quality of life.
Rapid changes in medication may aggravate symptoms in these children, and if possible, one medication at a time should be tried and a full assessment of that medication made before moving on to the next medication. Because of the tremendous variability in these children, an individualized approach is often necessary. Far too often, respiratory, nutritional and even physical rehabilitation interventions are reactive rather than proactive.
Future Treatment Directions
Better treatments for AHC may become a reality as we gain a better understanding of the disease, but progress to date has been extremely slow. Clinical trials to better assess the effects of medications on symptoms in AHC are desperately needed.
The relative rarity of this disorder makes it critical that families and physicians worldwide work together to gain a better understanding of the disease, and to collaborate in pursuing genetic studies and clinical trials. In the meantime, a proactive management strategy and a network of supportive health care professionals that you can rely on in a crisis situation are critical.
Good care is unlikely to be gained from the emergency room physician who has never heard of AHC. Rather, it is best to develop a proactive care plan, including contingent plans for emergencies. Participation in clinical studies and networking with other parents and support groups can help accelerate progress. Participation in studies is vital to the community to help demonstrate the effectiveness of potential treatments and to better understand this disease.
For more information about family support organizations for AHC, visit www.ahckids.org. To find out about participating in clinical studies on AHC or to join our AHC registry, contact us at the following:
Phone: (801) 587-9260