Episodic Ataxia and the Inability to Control Movement

Episodic ataxia is a group of uncommon disorders that cause periods during which a person is unable to control bodily movements (ataxia). There are eight types of episodic ataxia, but the first two are the best known.

Episodic Ataxia Type 1

The spells of unsteadiness caused by episodic ataxia type 1 (EA1) usually last only for minutes at a time. These periods are often brought on by exercise, ​caffeine, or stress. Sometimes there may be a rippling of the muscles (myokymia) that comes on with the ataxia. Symptoms usually begin in adolescence.

Episodic ataxia type 1 is caused by a mutation in a potassium ion channel. This channel usually permits electrical signaling in nerve cells, and these signals may become abnormal when the channel is changed by a genetic mutation. The easiest way to test for EA1 is to get genetic testing. An MRI may be done to rule out other potential causes of ataxia, but in the case of EA1, an MRI will only show mild shrinkage of the middle of the cerebellum which is called the vermis.

Episodic Ataxia Type 2

Episodic ataxia type 2 (EA2) is associated with attacks of severe vertigo and sometimes nausea and vomiting that last from hours to days. Nystagmus, a condition in which the eyes move repetitively and uncontrollably, can be present not only during but also between attacks. Unlike EA1, episodic ataxia type 2 can lead to injury to the cerebellum, the part of the brain responsible for coordination. Due to this slowly worsening damage, people with EA2 can lose voluntary control of the muscles in between their periodic attacks as well. Like EA1, people with EA2 usually first feel symptoms in adolescence.

Episodic ataxia type 2 is caused by a mutation in a calcium channel. This same calcium channel is also mutated in other diseases such as spinocerebellar ataxia type 6 and familial hemiplegic migraine. Some people with EA2 also have symptoms that are reminiscent of those other diseases.

Other Episodic Ataxias

The remaining episodic ataxia, types EA3 through EA8, are very rare. Many of the less common episodic ataxia are very similar in appearance to EA1 and EA2 but have different genetic mutations as the cause. Each of these subtypes has been reported in only one or two families.

• EA3 have brief attacks involving a lack of muscle coordination and control, with dizziness and muscle rippling.
• EA4 is more like EA2, with unusual eye movements like nystagmus that persists even when there is no active attack, though attacks are relatively brief. EA4 is unique in that it doesn’t respond well to the treatments used for other episodic ataxia.
• EA5 has attacks that go on for hours like EA2. It has been reported in a French Canadian family.
• EA6 is caused by a mutation that can also be associated with seizures, migraine, and hemiplegia, again like EA2.
• EA7 was identified in just one family and is very much like EA2 except that the neurological exam is normal in between attacks.
• EA8 shows its symptoms in early infancy with attacks lasting from minutes to a full day. It has been found within one family and responds to clonazepam.

Diagnosis of Episodic Ataxia

Before reaching a diagnosis of a relatively rare disorder like episodic ataxia, other more common causes of ataxia should be examined. However, if there is a clear family history of ataxia, it may be worth obtaining genetic testing.

Most physicians recommend working with a genetic counselor when seeking this kind of testing. While the results of a genetic test may seem straightforward, there are often important nuances that might otherwise be overlooked. It is important to know what a genetic test means not only for you but your family as well.

Treatment

Symptoms of both EA1 and EA2 improve with acetazolamide, a medication that is usually used as a diuretic or to help change acidity levels in the blood. Dalfampridine has also been shown to be effective in episodic ataxia type 2 as well. Physical therapy may be helpful to manage the ataxia when it is present.

While episodic ataxia is not common, a diagnosis has implications for both the patient and their family. It is important for neurologists and patients to think about episodic ataxia when there is a family history of clumsiness.