Lambert-Eaton Syndrome – Treatment, Symptoms, Pathophysiology

What is Lambert-Eaton Syndrome?

The Lambert-Eaton syndrome (LES), which is also associated with myasthenic syndrome, is a rare autoimmune disease that affects the neuromuscular process. Because the condition has similarities with the autoimmune disease myasthenia gravi, it is also identified as the Lambert-Eaton myasthenic syndrome.

By definition, the syndrome is characterized by muscle weakness primarily caused by interference in the neuromuscular junction. This should not be confused with Kearns-Sayre syndrome (KSS), which mainly affects the eyes and heart and which also causes weakness. Since KSS is a multi-systemic disorder, LES syndrome exhibits muscle weakness. There are also distinct differences between myasthenia gravis and LES.

LES greatly affects the release of acetylcholine (a smooth, cardiac muscle regulator and a neurotransmitter that is essential in skeletal movements) by disabling the presynaptic neuron responsible for the function. As a result, the patient will manifest muscle weakness and depressed or weakened tendon reflexes.

The condition was first described by Anderson in a cancer patient, while Lambert, Eaton, and Rooke published a report on the disorder, making it known to the public. The condition is more common in adults than in children and adolescents. The estimated number of LES cased is viable. About 40 percent of reported cases with small cell lung cancer are affected with the said syndrome; they account for 8 out of 1 million people with SCLS who are affected by LES.

Problem in acetylcholine release

Lambert-Eaton Syndrome Symptoms, Signs

LES is basically a progressive disease that affects the muscular system. The following are the enumerated signs and symptoms of the disease:

• Proximal muscle weakness affects muscle reflexes and pelvic muscles.
• Stretch reflexes are diminished or delayed. About 90 percent of patients manifest such signs.
• Strength is reduced in the lower extremities and more significantly, in the upper extremities.
• Myopathic gait, which is observed, is defined as waddling gait where weakness is prominent in the pelvic area, thus affecting the manner of walking.
• Ptosis (eye drooping) is not that severe or prominent compared to patients who have myasthenia gravis or KSS. Diplopia or double-vision is somehow prominent.

Presence of ptosis

• Weakness in the neck is prominent.
• Autonomic dysfunction is a common sign of LES. There will be dry mouth and sexual problems for men. Male impotence is a manifestation of about 45 percent of reported cases.
• The most crucial manifestation is the affectation of the lungs or respiratory system. Respiratory muscles are not spared, thus causing weakness. The patient then manifests difficulty in breathing. When the manifestation has not been controlled, the patient will suffer from respiratory failure.

Causes and Risk Factors

This autoimmune disorder, which affects the neuromuscular process (i.e., attacks the body’s own immune system) is mediated by antibodies. This rare condition is notably caused by an underlying cancer. It is apparent that those with small cell lung cancer (SCLC) are prone to such syndrome. About 40 percent of reported SCLC cases develop the syndrome. People who have other forms of cancer, such as  breast cancer, prostate cancer, and those which affect the hematologic system, were reported to have developed LES. The disorder is now the most common paraneoplastic syndrome – a syndrome that has emerged from cancer.

Diagnosis

A diagnosis of LES can be obtained through a physical examination. Obtaining the triad symptoms of the condition – proximal limb weakness, altered reflexes, and autonomic malfunction – would point to LES. The following are some of the considered (confirmatory) tests  for LES:

• Confirmatory test would involve the analysis of cerebrospinal fluid which would show the presence of a mild elevation of lymphocytic pleocytosis and protein level.
• Blood assessment for paraneoplastic antibodies is an indicator of an immune response to neoplasm/cancer.
• Electrodiagnostic studies, which include the use of nerve stimulation and assessment of muscle reaction and action potentials, will confirm the presence of LES.
• Electromyography is also done in order to identify any defect in the neuromuscular process and transmission.
• A chest CT or bronchoscopy is essential in order to identify the presence of lung cancer. This is mandatory and necessary to rule out malignancy.

Lambert-Eaton Syndrome Treatment

The treatment for LES is basically aimed at treating the underlying cause and presenting symptoms. The following are the proposed treatments for LES:

• When cancer has been detected, the patient will undergo chemotherapy. Immunotherapy, which is also essential, is only considered when the  patient has been unresponsive to the given drug treatment.
• Medications. Acetylcholinesterase inhibitors are provided to clients in order to reduce muscle weakness. This can be given in conjunction with guanidine hydrochloride which increases the action and effectiveness of the drug.
• Diaminopyridine is a drug of choice for people with LES symptoms. It blocks the potassium channels which are responsible for inhibiting nerve functions and action potentials.

Prognosis

The disease is identified as chronic and a completely disabling condition. Once early detection has been managed, the chance of having a better prognosis is present. Comparing it to myasthenia gravis, Lambert-Eaton syndrome is not much worse. However, when the case has been caused by an underlying lung disease, the condition can be hard to manage. It is important that treatment of an underlying condition is done to gain a better prognosis.

Life expectancy

The syndrome is considered a rare fatal disease. Since there are malignant disorders which are associated with LES, the life expectancy of the affected is somehow unfavorable. There is a survival rate of 10 to 16 months after diagnosis of the disease due to the underlying condition with which it came along. About 15 percent of people with LES have a 5-year survival rate, and patients with no associated malignant condition tend to have a limited survival rate.