Signs, Symptoms, and the Journey to Diagnosis

Navigating a diagnosis of Alternating Hemiplegia of Childhood (AHC) often begins with a long search for answers. Because AHC is a “great mimicker,” many children are misdiagnosed for years before the correct cause is found ^[1]. Understanding the difference between the sudden “spells” and the everyday symptoms is the first step in advocating for your child’s care.

The “Spells”: Paroxysmal Symptoms

AHC is defined by paroxysmal symptoms—episodes that come and go suddenly. These “spells” are the hallmark of the condition and can be frightening to witness ^[2].

• Hemiplegia (One-Sided Weakness): This is the sudden loss of muscle power on one side of the body. It may switch from one side to the other during a single episode, or it may affect the whole body (quadriplegia) ^[2].
• Dystonia (Muscle Twisting): Involuntary muscle contractions that cause painful twisting or stiff, unusual postures ^[3].
• Ocular Abnormalities: Unusual eye movements are often the very first sign. These include nystagmus (eyes shaking side-to-side) or eyes appearing crossed or fixed in one direction ^[2][4].

Explaining Spells to Others: Because AHC spells can closely resemble seizures to an untrained observer, it is highly useful to carry a brief “explanation card” or letter from your doctor. This can be given to teachers, daycare providers, or bystanders to explain what is happening, confirm it is not a seizure, and outline exactly what steps they need to take (and when to call 911).

Identifying Your Child’s Triggers

Most AHC episodes do not happen at random; they are “set off” by specific environmental or physical triggers. Identifying these can help you prevent or prepare for future episodes ^[5]. Common triggers include:

• Water and Temperature: Bathing, swimming, or even a sudden gust of cold wind are among the most common triggers reported by parents ^[5].
• Physical and Emotional Stress: Intense exercise, exhaustion, or being very excited or upset can trigger a spell ^[5].
• Sensory Input: Exposure to bright sunlight, flickering lights, or sudden loud noises ^[5].

Why Misdiagnosis is Common

Because AHC is so rare and its symptoms are “paroxysmal,” it is frequently mistaken for other conditions. Ending this “diagnostic odyssey” usually requires genetic testing of the ATP1A3 gene, which confirms the diagnosis in about 85% of cases ^[6][7].

Note: While AHC spells are not seizures, approximately 50% of children with AHC also have true epilepsy as a comorbid (occurring together) condition ^[10][11].

“Everyday” Symptoms: Non-Paroxysmal Impact

While the “spells” are the most visible part of AHC, the condition also causes persistent, non-paroxysmal symptoms that affect a child every day ^[3].

• Developmental Delay: Children often take longer to reach milestones like sitting up, crawling, or speaking ^[4].
• Ataxia (Balance Issues): A persistent “clumsiness” or difficulty with balance and coordination between attacks ^[12].
• Intellectual Disability: Many children face cognitive challenges, though the severity varies widely based on their specific genetic mutation ^[6][6].
• Behavioral Challenges: Some children may struggle with social impairments or behavioral problems ^[13].

Understanding these everyday challenges is just as important as managing the spells, as they often require ongoing support through physical, occupational, and speech therapy ^[12].