Our bodies’ nerve cells are important for transmitting electrical and chemical information between different parts of the brain and between the brain and other parts of the nervous system.
One of the most important roles of your body’s nerve cells, or neurons, is to carry information that directs your movements.
The neurons that control muscle movement, known as motor neurons, are located in the brain, spinal cord, and peripheral nerves. These neurons work together to move muscles in your body.
The upper motor neurons are located in the brain and spinal cord, and the lower motor neurons are in the peripheral motor nerves.
Sometimes, motor neurons can become damaged, potentially impairing mobility. Injuries can cause damage to upper motor neurons, lower motor neurons, or both.
Injuries to the upper motor neurons can occur from illnesses, physical trauma, and vitamin deficiency. The word lesion refers to the area of damage on a neuron.
Upper motor neuron lesions can result in muscle weakness, muscle wasting, overreactive reflexes, spasms, and other issues that can impair mobility.
What are lower motor neuron lesions?
It’s also possible for lower motor neurons to develop lesions. Common causes of lower motor neuron lesions include physical trauma and illnesses. Lesions on lower motor neurons most commonly cause:
Upper motor neuron lesions can have a variety of causes spanning physical trauma, illness, and vitamin deficiency. Several of the most common causes of upper motor neuron lesions include:
- multiple sclerosis (MS)
- B12 vitamin deficiency
- Brown-Sequard syndrome (spinal hemiplegia)
- trauma to the brain or spinal cord
- severe brain infection
Additionally, amyotrophic lateral sclerosis (ALS), also known as Lou Gehrig’s disease, and primary lateral sclerosis cause both upper and lower motor neuron degeneration.
Each condition that causes upper motor neuron lesions comes with its own set of signs and symptoms.
However, most causes of upper motor lesions share the same core symptoms, which tend to affect large groups of muscles from different body parts. These include:
- muscle weakness
- increase in muscle tone
- increased muscle stretch reflex
- clonus, or involuntary and rhythmic muscle contractions at the ankle, patella, triceps, wrist, jaw, and biceps
- temporary flaccid paralysis
- muscle spasms
- Babinski sign
A late-stage effect of not using the muscles enough is low to moderate muscle wasting.
The goal of diagnosing upper motor neuron lesions and its cause or causes can help address any underlying problems resulting in upper neuron damage. A proper diagnosis can also minimize symptoms of existing damage.
The earlier signs of upper motor neuron lesions are diagnosed, the better chances of minimizing damage to the brain and nervous system.
A medical professional will first take your medical history and perform a physical exam. This will determine whether you have an upper motor neuron disorder or a lower motor neuron disorder.
From there, they’re likely to perform tests on your stretch reflex. One of the more common tests is the test of the myotatic reflex, or the “knee-jerk” reflex.
Some features that point to an upper motor neuron disorder include:
- weakness on one side of the body
- sensory loss on one side of the body
- increased reflexes
- accompanying symptoms like headaches or confusion
Some features that point to a lower motor disorder include:
- sensory changes
- weakness in both feet or both hands
Diagnostic tests for evaluating upper motor neuron disease include imaging tests of the brain or spine as well as lumbar puncture.
Arriving at a diagnosis of upper motor neuron lesions can help a medical professional best develop an effective treatment plan.
Treatment for upper motor neuron lesions varies depending on the cause that resulted in lesions. Some common treatments include:
- physical therapy and rehabilitation
- a balanced diet, with supplementation when necessary
- muscle relaxers and botulinum toxin (Botox), which are treatments for severe spasticity that can occur with late stage upper motor neuron disease, when people are not mobile
- treatment of the underlying cause, such as MS-modifying treatment or medication prescribed for dementia
- brain tumor removal surgery
- medications like riluzole or edaravone, which are used specifically for ALS
Many conditions causing upper motor neuron lesions are serious and can cause long-term, irreversible deterioration of the brain and body.
The outlook for issues causing upper motor neuron damage varies depending on factors like age of onset.
While causes of upper motor neuron lesions are serious, many are not fatal and progress slowly over time.
Early diagnosis can help prevent continued damage to the upper motor neurons and help protect remaining mobility and muscle function.
Supplementary treatments like physical therapy can help strengthen the body and alleviate symptoms of upper motor neuron lesions, particularly those that impair mobility.
Our bodies’ movements are directed by electrical and chemical signals that pass through the body’s upper and lower motor neurons. Physical trauma, disease, and vitamin deficiency can cause upper motor neuron lesions.
Early diagnosis and full treatment of the underlying cause or causes of upper motor neuron lesions can help improve outcome, minimizing symptoms and slowing symptom progression.
Contact a doctor if you’re experiencing unusual muscle weakness, movements, or wasting.