Alien Hand Syndrome: When One Limb Develops a Mind of Its Own

When a single limb moves involuntarily, it can signify a serious underlying medical condition, such as stroke or neurodegenerative disease. This is also known as alien hand syndrome.

What Is Alien Hand Syndrome?

Brain and nerve damage is usually associated with loss of control over the areas of the body associated with the damage. For instance, paraplegics may lose control over their legs after a spinal cord injury. However, there are also cases when the damage does not stop the movement of the limb, and instead gives it a mind of its own.

Known as alien hand syndrome (AHS), this rare neurological condition causes one hand to act on its own free will. One leg can also be affected, although this one is not as common. Adults are usually affected by this condition, but it can also be experienced by children.

Alien hand syndrome is also called anarchic hand or Dr. Strangelove syndrome and it was first described in 1908. In this type of disorder, the hand is not under the control of the brain and instead moves as though it has its own mind. During these episodes, the affected hand feels foreign to its owner and seems to carry out tasks that are unintentional.

There are three main categories of this disease based on the part of the brain that is causing the condition. These regions could be frontal lobe, callosal lobe, and parietal lobe. The exact symptoms of alien hand syndrome also depend on the version developed on a patient.

For the frontal lobe version, the symptoms include involuntary groping and grasping and difficulty releasing objects. In the posterior (parietal) version, a person experiences levitation of the arm, less purposeful movement, and psychological struggles. Meanwhile, the callosal version is characterized only by conflict during two-handed tasks.

AHS is so rare that there are only a few reported cases in the scientific literature. Some doctors may not also be familiar with this medical condition.

What Causes Alien Hand Syndrome?

There is no one universal cause for alien hand syndrome, since it is brought by several factors. It is always caused by damage to the brain, which disrupts a person's movement and control.

In rare cases, the posterior variant of AHS is developed after an ischemic or hemorrhagic stroke. Neurodegenerative diseases, like Alzheimer's disease or Parkinson's disease, are also leading causes of alien hand syndrome. Other causes may also include midline tumor and aneurysm.

This medical condition is also linked to brain surgeries which separate the two hemispheres of the brain. This could involve an incision along the corpus callosum, the region of the brain that divides the hemispheres and enables communication between the two sides.

No approved or recommended treatments for alien hand syndrome currently exist. Some studies, however, noted that certain tasks and exercises can improve the symptoms of this disorder.

A 2021 research suggests that patients with AHS experience the most improvement after doing bimanual tasks and those that involve various colors. It is believed that colors may help to gain a person's attention to one particular side of the body.