Skin Test May Confirm Autonomic Nerve Disorders in LEMS Cases

Patricia Inácio, PhD avatar

by Patricia Inácio, PhD |

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A simple, noninvasive test on the skin, called skin sympathetic response, can be used to confirm impairments in the autonomic nervous system — the non-conscious part of the nervous system that controls several bodily functions — in people with Lambert-Eaton myasthenic syndrome (LEMS), according to a case study.

The study, “Autonomic dysfunction detected by skin sympathetic response in Lambert-Eaton myasthenic syndrome: a case report,” was published in BMC Neurology.

LEMS is a rare autoimmune disease wherein the body’s immune system wrongly launches an attack against specific calcium channels called voltage-gated calcium channels (VGCCs) that play a key role in nerve-muscle communication and muscle contraction. It is usually associated with an underlying cancer, most often small-cell lung cancer (SCLC).

More than 50% of LEMS patients have signs of autonomic dysfunction, such as dry mouth and eyes, constipation, impaired sweating, and orthostatic hypotension, which causes blood pressure to suddenly drop when a person stands up from sitting or lying down.

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Researchers in China described the case of a 75-year-old man with autonomic dysfunction associated with LEMS that was confirmed by a noninvasive skin test.

The patient had an uneventful medical history, in general. However, he had dry mouth and constipation for the past two months, and muscle weakness for a month.

No tendon reflexes were registered across any of his limbs. He showed signs of orthostatic hypotension, but had a positive response on a skin scratch test.

Chest and brain MRI scans, ultrasounds of the abdomen and lymph nodes, as well as blood tests showed no signs of an underlying tumor.

An electromyography (EMG) test, which records electrical signals coming from muscles in response to nerve signals, and nerve conduction velocity (NCV) tests showed no signs of muscle or nerve damage. NCV tests measure how well and how fast electrical impulses move through nerves.

The patient also underwent low-frequency (3 Hz) and high-frequency (20 Hz) repetitive nerve stimulation (RNS), which uses electrodes to measure a nerve’s ability to send electrical signals to muscle tissue. Electrodes are usually placed on a patient’s skin over the muscles clinicians wish to test.

RNS was conducted in the right and left peroneal nerve, a branch of the sciatic nerve that supplies movement and sensation to the lower leg, foot, and toes. Results from the 3 Hz RNS test showed a 30% decrease in muscle response on the right nerve, and 32% on the left nerve.

He was positive for VGCC antibodies, and, considering all the test results, he was diagnosed with LEMS.

Since he had prominent symptoms of autonomic dysfunction, he had a skin sympathetic response (SSR) test to confirm it. This test, which has not been widely performed on LEMS patients, measures changes on the electrical potential of the skin. It was conducted in the palms of his hands and the soles of his feet.

The first test revealed lower responses on both palms, and no response was recorded after three other stimulation attempts on his soles.

He was treated with a five-day course of immunoglobulins delivered directly into the bloodstream.

At the time of publication, he had been followed for six months. He recently had muscle weakness and difficulties walking, but has not had dry mouth and constipation.

Chest CT and blood tests done every three months showed no signs of a tumor.

“In this case, we present the detailed results of SSR test on a patient suffering LEMS and autonomic disorder simultaneously. Since SSR test is an effective way to detect autonomic dysfunction, we recommend that SSR test be performed on patients with LEMS regularly,” the researchers wrote.