Split hand syndrome is a potential sign of amyotrophic lateral sclerosis (ALS). This means that some of the muscles in the hand are weak and thin (atrophied), while others are less affected.

Healthcare professionals describe the condition as “split” within the hand’s appearance and function.

While split hand syndrome may suggest ALS, a doctor cannot diagnose ALS with a hand examination alone. They must also perform tests to rule out other possible underlying conditions.

This article will review split hand syndrome, its causes, how it can help diagnose ALS, and treatment options for split hand syndrome in ALS.

What is split hand syndrome in ALS?

Black and white image of a hand -1. — Maite Pons/Stocksy United

Split hand syndrome is a symptom that may develop in the hands of people with ALS. People with split hand syndrome show muscle wasting near the thumb, while the muscles on the opposite side near the little finger are less affected.

Muscle wasting refers to a loss in muscle mass that can occur when the muscle weakens or shrinks.

Split hand syndrome in people with ALS may occur alongside other symptoms, including:

loss of motor control in the fingers and hands
frequent tripping and falling
persistent fatigue
difficulty grabbing objects or performing complex tasks with the hands due to muscle weakness
cramping and twitching of muscles, particularly in the limbs
slurred speech

As the illness progresses, a person may also experience symptoms such as:

an inability to control arm and leg movements
difficulty swallowing or chewing
difficulty breathing
muscle paralysis

Learn more about ALS.

What causes split hand syndrome in ALS?

Doctors think this phenomenon may occur because of the damage that ALS causes to motor neurons, which are cells of the spinal cord.

It is not completely clear why the particular split-hand pattern of weakness and atrophy develops in some people with ALS. Some research suggests it could be related to how people preferentially use certain hand muscles or the progression of motor neuron damage in the spinal cord.

Not everyone who has ALS has split hand syndrome. Many people with ALS develop weakness of the whole hand at the same time.

When to see a doctor about split hand syndrome

A person should immediately speak with a doctor if they experience split hand syndrome or notice any ALS-related symptoms. Doctors can perform a series of tests to diagnose the underlying cause and discuss the next steps a person should consider.

A prompt diagnosis and treatment can help slow the progression of the condition and improve the overall life quality of a person with ALS.

Diagnosis of split hand syndrome in ALS

Specialists can use the split hand index to assign a score to the muscle wasting of the hand in a person with suspected ALS. The score indicates the person’s ability to perform certain movements using the muscles in their hand. Doctors can repeat the test periodically to assess the progression of ALS and muscle wastage.

Doctors may perform other tests if the split hand test suggests ALS or they strongly suspect someone has the condition. People should note there is no single test that can diagnose ALS.

Diagnosing ALS usually requires a comprehensive review that combines the results of several physical exams with a person’s medical history.

People may need to undergo certain physical tests at regular intervals to assess whether the symptoms are stable or worsening over time.

Additional exams doctors may perform to rule out other possible health conditions and help with the diagnosis of ALS include:

a nerve conduction velocity test
blood and urine tests
an electromyogram (EMG)
a nerve and muscle biopsy
an MRI scan
a lumbar puncture, also called a spinal tap

These tests can help check whether nerves and muscles can send and receive electrical impulses and perform instructions.

Some of these tests can detect diseases affecting the spinal cord that could be causing ALS-like symptoms. The tests can also rule out other health conditions.

Learn more about ALS diagnosis.

Treatment for split hand syndrome in ALS

There is no specific treatment for split hand syndrome. Treating split hand syndrome does not help delay ALS progression, nor does it treat ALS as a whole.

However, physical therapy and supportive devices can focus on specific muscles affected by ALS, including the hand muscles.

ALS treatment

There is no cure for ALS at this time. However, several treatments can help slow the progression of the disease, extend a person’s life, and improve their quality of life.

Treatment involves drug therapies such as:

riluzole (Rilutek, Tiglutik, Exservan)
tofersen (Qalsody)
edaravone (Radicava)
sodium phenylbutyrate/taurursodiol (Relyvrio)

Someone with ALS may receive a personalized treatment plan that incorporates different therapy types, such as:

In the later stages of ALS, people may require additional care.

Learn more about ALS medications.

Summary

Split hand syndrome is a potential sign of ALS. It means there is weakness and muscle loss in the parts of the hand near the thumb and nearly normal strength and muscles near the little finger.

If someone notices symptoms of split hand syndrome, they should speak with a doctor.

Doctors will use a variety of tests if they suspect a person of having ALS. This helps rule out other conditions that could be causing ALS-like symptoms.

One test is known as a split hand index. Doctors may repeat this test to determine the level of muscle wastage and identify whether the disease is progressing. There is no single test that can diagnose ALS.

What to know about split hand syndrome in ALS