Know about Lambert Eaton vs Myasthenia gravis USMLE

Lambert Eaton myasthenic syndrome (LEMS) is an autoimmune disorder of presynaptic neuromuscular junction(NMJ) which is associated with antibodies against the voltage-gated calcium channel. This disease present similar to Myasthenia gravis (MG), except the weakness improves with exercise, and hyporeflexia and dysautonomia are present. Most cases of LEMS occur among middle-aged adults, but it can affect younger and older adults.

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Clinical features of Lambert eaton myasthenic syndrome

The triad of Lambert-Eaton myasthenic syndrome (LEMS) is proximal muscle weakness, autonomic dysfunction, and absent deep tendon reflexes. Symptoms are usually insidious in onset and progress more rapidly in small cell lung cancer. Remember the key difference between lambert Eaton vs myasthenia gravis is muscle weakness that improves after prolonged use.

Muscle weakness:
- Proximal limb weakness
Postexercise or post-activation facilitation
- improvement in muscle strength with vigorous brief muscle use
Ptosis and cranial nerve involvement: are the most common cranial nerve manifestations of Lambert-Eaton myasthenic syndrome. Dysphagia and dysarthria also are seen.
Autonomic dysfunction
- Dry mouth.
- Erectile dysfunction in men,
- Constipation
- Orthostatic dysfunction
- Altered perspiration.
Respiratory failure infrequently.

How is Lambert Eaton myasthenic syndrome (LEMS) diagnosed?

Diagnosis can be confirmed by.

Electrodiagnostic studies, including repetitive nerve stimulation (RNS)
Serology: anti-P/Q-type voltage-gated calcium channel (VGCC) antibody
Screening for Malignancy like Small cell lung cancer and Hodgkin lymphoma using CT scan of chest

Differential Diagnosis of Lambert Eaton myasthenic syndrome

The differential diagnosis of Lambert Eaton myasthenic syndrome (LEMS) includes all diseases presenting with progressive muscle weakness like

Amyotrophic lateral sclerosis
Myasthenia gravis
Multifocal motor neuropathy

How do you treat Lambert Eaton myasthenic syndrome (LEMS)?

Treat underlying malignancy, usually SCLC
Firdapse (amifampridine) is an FDA-approved medication for the relief of LEMS symptoms.
- Mechanism of action: Potassium channel blocker which increases the calcium influx into the nerve endings, helping the release of acetylcholine.
3,4-diaminopyridine or guanidine can be given
Cholinesterase inhibitors eg. pyridostigmine can be used.
Immunosuppressive medications such as Corticosteroids and azathioprine can help control symptoms if the autoimmune cause is suspected, rather than malignancy.
Plasmapheresis can help relieve LEMS symptoms.
Intravenous immunoglobin (IVIG) is thought to inhibit the immune system’s production of autoantibodies.