Distinguishing Carpal Tunnel Syndrome and LEMS

Many of the symptoms of Lambert-Eaton myasthenic syndrome (LEMS) — notably muscle weakness, pain, and fatigue, as well as tingling in the hands and feet — can be very similar to another condition called carpal tunnel syndrome. It can, therefore, be difficult to distinguish the two conditions.

LEMS is a rare autoimmune disease that affects the neuromuscular junction, the point at which nerve and muscle cells meet. In people with the disease, the immune system mistakenly attacks a particular component of the nerve cell called the voltage-gated calcium channels. These channels are responsible for transmitting information from nerve cells to muscle cells. Without this channel, nerve signals become weaker but are usually not lost altogether.

People with LEMS often report experiencing muscle weakness, pain, and fatigue. Tingling in the hands and feet also can occur. Similar symptoms also can be caused by carpal tunnel syndrome, which affects one of the major nerves to the hand, called the median nerve.

What is carpal tunnel syndrome?

The carpel tunnel is a passage of muscle and sinew running along the palm side of your hand and arm. Along this groove, the median nerve conducts information from the brain to the muscles of the arm and hand. It also conducts sensory information — such as pain, temperature, and feeling — from the arm and hand back to the brain.

Repetitive motion that compresses the median nerve can cause carpal tunnel syndrome and lead to pain, tingling, numbness, and difficulty moving the hand and arm. Other risk factors can include inflammatory conditions, medications, obesity, and workplace factors.

How can doctors distinguish the two conditions?

A small case study showed that it is possible to distinguish LEMS from carpal tunnel syndrome by using a diagnostic test called post-exercise facilitation (PEF). PEF tests reflexes in the arms following exercise. In this case, this was done by having a male patient clench his hands for 20 seconds. The results showed that muscle activity in the patient’s left arm improved following PEF. However, it remained the same in the right arm. The researchers concluded that the cause of the muscle weakness was neuromuscular junction dysfunction in the left arm and carpal tunnel syndrome in the right arm. They suggested that PEF could distinguish between the two conditions.

However, another study involving 16 LEMS patients indicated that, in legs and feet, PEF is not detectable in most cases. Therefore, more studies involving more LEMS patients may be necessary to determine whether this test is useful in all cases.

Moreover, no studies have demonstrated whether carpal tunnel syndrome is more common in LEMS patients. It is possible that, due to immune system attacks, the median nerve is more fragile and easily damaged. However, researchers have not demonstrated this.

How do doctors treat carpal tunnel syndrome?

A small surgery may be used to relieve the pressure on the median nerve. By cutting one ligament in the wrist, the pressure on the nerve can be lessened, reducing the pain and tingling sensations.

Doctors may treat some patients with a wrist brace that prevents them from making repetitive motions, which can cause carpal tunnel syndrome.

Last updated: Aug. 3, 2020

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