Dysmetria is a lack of coordinated movement occurring due to damage to your cerebellum. We will look at the causes and symptoms of this condition and how it’s diagnosed and treated.
What Is Dysmetria?
Medical experts use the term “cerebellar ataxia” when referring to conditions that lead to a lack of muscle control. Dysmetria is one form of cerebellar ataxia.
Dysmetria occurs due to the improper functioning of the cerebellum. Your cerebellum (also known as the little brain) is a structure located at the back of your head below the occipital and temporal lobes of the cerebral cortex.
Although the cerebellum makes up only a small part of the brain structure, it houses more than 50% of the total neurons in the brain. This region of the brain carries out many vital functions.
- Balancing the body. The cerebellum helps you balance by changing your posture when necessary. It regulates the motor neurons (neurons responsible for carrying out movements) to shift your stance and maintain balance using different muscles.
- Regulate motion. Every movement of your body is the result of the combined activity of several muscles. One of the primary functions of the cerebellum is to regulate the timing of movements and direct various muscle groups.
- Accurate movements. Your cerebellum is vital, adjusting and modifying your motor actions to complete precise movements based on practice. For example, kicking a football becomes easier with more practice due to the cerebellar functions that regulate the muscles in your eyes, feet, and other body parts.
- Cognitive abilities. While the cerebellum is mainly concerned with motor control, critical cognitive functions like language also depend on this organ. Still, more research is needed to understand how it contributes to these functions.
Dysmetria affects these functions of the cerebellum.
Dysmetria can occur in combination with other symptoms such as ataxia and tremors. You may face difficulty deciding when to begin and end movements if the nerves that relay information to your cerebellum are affected.
People with dysmetria typically cannot judge the distance between themselves and the objects they are trying to reach or walk toward. This causes them to either overreach (or overstep), leading to what is known as hypermetria. On the other hand, they may also underreach (or take a smaller step than needed), a condition labeled hypometria. Hypermetria tends to be more common than hypometria.
In some cases, dysmetria also affects other cerebellar functions, leading to a lack of control over balance, gait, speech, and eye movements.
Damage to the cerebellum can cause dysmetria—more specifically, damage to those parts of the cerebellum that regulate motor, spatial, and other inputs necessary to carry out movements and maintain the body’s balance. This can be due to:
- Brain infections (encephalitis)
- Degenerative conditions like Friedreich’s ataxia or spinocerebellar ataxia
- Conditions like cerebral palsy, stroke, and other autoimmune diseases
- An injury to the brain following an accident or other impact
- Brain tumors
- Metabolic diseases like Hartnup disease and Salla disease. Some conditions may impact normal enzyme functions and cause a deficiency of certain nutrients, such as thiamine, cobalamin, and riboflavin. Conditions like Leigh’s disease, meanwhile, may affect the central nervous system. They are caused by the deficiency of specific enzymes.
- Conditions that cause demyelination. Demyelinating diseases damage the myelin sheath: the layer that protects the nerve fibers in your brain, the optic fibers that connect to your eyes, and the spinal cord. Damage to the myelin sheath affects nerve activity and, in some cases, completely blocks their function, which causes neurological issues. One such condition that causes demyelination is multiple sclerosis.
Other causes include inherited neurotransmitter disorders due to genetic defects that damage neurotransmitters and affect brain functions.
How Is Dysmetria Diagnosed?
Doctors usually carry out a few tests to determine whether you have dysmetria: These dysmetria tests include the:
- Finger-to-nose test. Your doctor will ask you to reach out and touch one of their fingers and then touch your nose with the same finger. If you have dysmetria, you will feel a tremor in the arm on the same side where there is damage to your cerebellum as your finger comes close to your nose. This tremor occurs due to the loss of coordinated movements.
- Heel-to-shin test. This test is used to determine if you have coordination issues in your lower limbs. Your doctor will ask you to place one heel on the shin of the other leg and roll the heel from the knee down toward your foot a few times. People with dysmetria will be unable to trace a straight line.
Your doctor will decide on the best treatment for this condition depending on what has caused cerebellar damage and its seriousness. Modern science has yet to find a permanent cure for dysmetria, but physical and occupational therapy have helped improve motor functions.
Physical therapy aims to restore muscle strength, and occupational therapy involves working with specialists who can help you recover and learn the skills necessary to lead a normal life.
What to Know About Dysmetria
Dysmetria could impair your coordination and vision. Motor dysmetria, for instance, is an inability to determine your location in space – in relation to objects around you. This causes you to misjudge the distance between yourself and the object. For example, when you try to reach out to a chair near you, you typically end up either not moving your hand enough to touch it or moving it much farther than the chair’s location.
Saccadic dysmetria, meanwhile, leads to sporadic eye movements.
Ocular dysmetria is an inability to focus and a tendency to misjudge distances.