Lambert-Eaton-syndrome G73.-

Edward Lambert and Lee Eaton neurologists at the Mayo Clinic in Rochester, Minnesota, who first described myasthenic syndrome in the 1950s and '60s.

Lambert-Eaton myasthenic syndrome (LEMS) is an autoimmune disorder - a disease in which the immune system interferes with the connection between nerves and muscles (the neuromuscular junction) and impairs the ability of nerve cells to send signals to muscle cells.

Compared to myasthenia gravis, Lambert-Eaton syndrome is a much rarer neuromuscular disease characterized by a presynaptic disturbance of neuromuscular signal transmission. The syndrome is based on an autoimmune process with the formation of antibodies directed against voltage-dependent calcium channels of the P/Q type. As a result, there is decreased transmitter release at the cholinergic synapses of both the motor and autonomic nervous systems.

Two variants are distinguished:

• Paraneoplastic: In approximately 40-60% of cases, LEMS may be preceded by a tumor (usually a small cell lung carcinoma) up to a maximum of five years. LEMS symptomatology offers the chance of early tumor diagnosis!
• Idiopathic: If no tumor has manifested 2-3 years after the onset of LEMS, this speaks for a purely autoimmunologically induced variant of LEMS.

In about 50-60% of cases, LEMS is associated with an underlying disease, especially small cell lung cancer. In 40-50% of cases, the cause is unknown. Specifically, the immune system attacks the calcium channels at nerve endings that are required to trigger the release of acetylcholine. When there are fewer calcium channels, the nerve terminal releases less acetylcholine. Acetylcholine is a neurotransmitter that triggers muscle contraction. In people with LEMS, decreased acetylcholine levels are not enough to trigger normal muscle contractions, resulting in muscle weakness.

Initially, LEMS causes motor dysfunction in the thighs and hips, resulting in difficulty walking, and weakness in the upper arms and shoulders, which can make self-care difficult. Specifically, the clinical picture is characterized by the following symptoms:

Motor dysfunction (motor symptoms are initially severe under exertion, may improve briefly when exertion is continued - warming up-. Contrary to myasthenia, however, a Lambert-Eaton affected person does not recover after a period of rest!

Pelvic and thigh muscles (in 100% of patients):

• Weakness and very rapid fatigability when walking, standing up from a sitting position and climbing stairs.
• Reduced walking distance (sometimes less than 100 m)
• "Lead shoes" and waddling gait
• Tendency to trip
• Weakened muscle reflexes
• Myalgias (muscle pain) possible

Upper arm muscles/ shoulder apparatus

• in 80 % of patients

Eye muscles

• Less pronounced; eye symptoms may increase in the course of the disease

Involvement of facial and swallowing muscles

• Less frequent

Cranial nerve symptomatology (in about 60% of patients):

• Ptosis (drooping of one or both eyelids)
• Double vision

Autonomic disorders:

• Dry mouth
• Constipation/ bladder dysfunction
• Orthostatic hypotension
• Decreased sweating

EnG according to Willkürinnovation (Electroneurography is a neurological examination method with which the nerve conduction velocity is measured. Electroneurography is applicable to nerves supplying muscles (motor nerves) as well as to nerves responsible for sensations (such as temperature or touch stimuli) (sensory nerves).

Serial stimulation:

• 3 Hz: pathological decrement
• 20-50 Hz: pathological increment

Laboratory: Antibody detection

Combination of LEMS and myathenia gravis is rare but possible:

Oculobulbar symptomatology

Positive tensilon test

AK against the acetylcholine receptor and AK against P/Q-type calcium channels.

Electrophysiological: LEMS triad

• AK against P/Q-type calcium channels (VGCC) undetectable in 10% of patients
• AK against SOX1 tumor antigen
• AK against acetylcholine receptor