Ach/NMJ Disorders - Myasthenia Gravis and Lambert-Eaton Syndrome

A collection of flashcards covering the key terms, definitions, and concepts related to Myasthenia Gravis and Lambert-Eaton Myasthenic Syndrome.

Myasthenia Gravis

An autoimmune disorder of the neuromuscular junction characterized by fluctuating skeletal muscle weakness that worsens with activity and improves with rest.

Fluctuating muscle weakness

A symptom of Myasthenia Gravis where muscle strength worsens with activity and improves with rest.

Ocular symptoms

Symptoms such as ptosis and diplopia observed in approximately 60% of Myasthenia Gravis patients at onset.

Acetylcholine receptor (AChR)

The key postsynaptic protein targeted by autoantibodies in Myasthenia Gravis.

Nicotinic acetylcholine receptor

A receptor that binds acetylcholine and plays a crucial role in muscle contraction.

Muscle-specific kinase (MuSK)

A protein that is also targeted by autoantibodies in Myasthenia Gravis.

Thymoma

A tumor of the thymus gland which can be associated with Myasthenia Gravis.

Electromyography (EMG)

A diagnostic test used to assess the health of muscles and the nerve cells that control them.

Repetitive nerve stimulation (RNS)

A test that shows a decremental response in Myasthenia Gravis patients.

Edrophonium test

A historical test used to diagnose Myasthenia Gravis by temporarily improving muscle strength.

Lambert-Eaton Myasthenic Syndrome (LEMS)

A rare autoimmune neuromuscular disorder that disrupts communication between nerve cells and muscles.

Presynaptic nerve terminals

The site at which LEMS autoantibodies disrupt acetylcholine release.

Proximal muscle weakness

A hallmark symptom of LEMS typically beginning in the legs and hips.

Hyporeflexia

A condition in which muscle stretch reflexes are reduced or absent, associated with LEMS.

Antibody Testing

Testing for specific antibodies, such as anti-VGCC, to help diagnose LEMS.

Voltage-gated calcium channels (VGCC)

Channels that are critical for triggering acetylcholine release, targeted in LEMS.

Paraneoplastic syndrome

A syndrome associated with cancer, such as LEMS being linked to small cell lung cancer (SCLC).

Autoantibodies

Antibodies that mistakenly target and react with a person's own tissues, causing disorders like MG and LEMS.

Electrophysiologic abnormalities

Distinctive features seen during tests like RNS that help diagnose conditions like LEMS.

Cancer screening

Required for all LEMS patients to check for underlying malignancies such as small cell lung cancer.

Myasthenic crisis

A severe exacerbation of symptoms in Myasthenia Gravis leading to respiratory failure.

Acetylcholinesterase inhibitors

Medications (e.g., pyridostigmine) that increase acetylcholine availability at the NMJ for MG treatment.

Corticosteroids

Immunomodulatory agents used in the treatment of Myasthenia Gravis.

Eculizumab

A targeted biologic used in the treatment of Myasthenia Gravis that inhibits complement activity.

Amifampridine

A drug that increases acetylcholine release by blocking presynaptic potassium channels, used in LEMS treatment.

Diminished Deep Tendon Reflex (DTRs)

A reduction in reflexes often observed in patients with LEMS.

Post-exercise facilitation

Temporary improvement in muscle strength observed in muscle tests after brief exercise in LEMS.

Calcium influx

The entry of calcium ions into the presynaptic nerve terminal, essential for acetylcholine release.

PEP (Potential End-plate)

The potential needed at the muscle fiber for action potentials, reduced in Myasthenia Gravis.

Complement-mediated damage

Damage to the postsynaptic membrane in Myasthenia Gravis due to immune system actions.

Latin term for severe muscle weakness

The historical derivation of the term Myasthenia Gravis.

Thymectomy

Surgical removal of the thymus, indicated for some Myasthenia Gravis patients.

Immunosuppressive therapy

Treatment option for LEMS involving corticosteroids or other agents to reduce immune response.

Neostigmine

An anticholinesterase agent used to treat symptoms of Myasthenia Gravis.