Neuro Disorders: Lambert Eaton Myasthenia Syndrome

Introduction

Lambert Eaton Myasthenia Syndrome (LEMS) is an uncommon neurological illness.

It results due to a dysfunction at the NMJ (neuromuscular junction) level and presents with muscle weakness. It is also called as Eaton Lambert Syndrome.

Lambert Eaton Myasthenia Syndrome is an autoimmune disorder meaning, your body immunity, rather than helping on the contrary actually troubles you. It acts as if your body is alien to it and mounts an attack on different tissues and/or organs depending upon the type of autoimmune disorder.

With LEMS the dysfunctional immune system targets mainly the skeletal (voluntary) muscles.

NMJ is the area where a motor nerve fiber links with a muscle fiber and transmits nerve impulses from the brain and spinal cord to the muscles so that muscle can get activated and do its function.

LEMS is most often a paraneoplastic disorder, means there could be an underlying malignancy that can trigger LEMS. SCLC (Small cell lung cancer) is the commonest malignancy that is associated with LEMS. Paraneoplastic Disorder is a type of disease process secondary to the effects of a tumor at a distant site from the tumor).

What causes LEMS?

As noted above it is an autoimmune disease. There are abnormal antibodies produced in the patient’s body that target certain types of (voltage gated type) calcium channels situated in the presyaptic area of the NMJ. This results in a deficiency of liberation of the neurochemical or neurotransmitter Ach (acetylcholine) and this causes muscle weakness.

Note that not all LEMS patients show these antibodies.

Who gets LEMS?

Majority of the patients are middle or old aged. Both genders, all races & ethnicities are affected.

Clinical Presentation

The following manifestations are seen in a typical case.

In the early stages the leg muscles are more prominently involved than the arms or facial/eye/bulbar muscles. Proximal muscles are more involved than the distal ones. As disease advances the disease can involve muscle more diffusely and so arms, facial/eye/bulbar muscle involvement can be seen too.

Patients will complain of difficulty with walking, rising from a sitting or lying down position early in the disease. Later lifting objects with arms especially above the shoulders, drooping of eye lids, double vision etc is seen. In advanced and serious forms respiratory muscle weakness will produce difficulty with breathing.

Patients frequently have decreased deep tendon reflexes. After some exercise there could be temporary improvement in the muscle strength and the reflexes.

If LEMS patient has an underlying tumor like lung cancer then there are additional manifestations secondary to that like cough, sputum, blood in the sputum, weight loss etc.

Diagnosis

It is a relatively rare disease so a high index of suspicion is necessary. The following investigations are usually required;

• Blood tests including ESR/CRP, CPK, LDH, auto antibodies against voltage gated calcium channels, thyroid tests etc

• EMG (electromyography)
• RNS (repetitive nerve stimulation) at both low & high frequency stimulation
• SFEMG (single fiber EMG)
• CT chest etc to look for underlying malignancy

Treatment

For an acute severe attack;

• Immunoglobulin or
• Plasmapheresis etc are used.

For maintenance therapy;

• Pyridostigmine (cholinesterase inhibitors)
• Guanidine
• 4 Aminoipyridine etc are used

A neurologist is frequently involved in the care of patients with Lambert Eaton Myasthenia Syndrome.



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