From the Guidelines
Acetylcholine receptor antibody titers are typically negative in Eaton-Lambert syndrome, also known as Lambert-Eaton Myasthenic Syndrome (LEMS). The diagnosis of LEMS is generally based on clinical characteristics, electromyography, and the presence of antibodies against voltage-gated calcium channels (VGCCs) 1. The study by the American College of Chest Physicians 1 highlights that more than 90% of LEMS patients have antibodies against VGCC type P/Q, which is the primary etiology for LEMS. Key characteristics of LEMS include:
- Craniocaudally progressive proximal muscle weakness
- Predominant weakness at the hip girdle
- Presence of anti-VGCC antibodies
- Electromyography showing characteristic incremental response to repetitive nerve stimulation In contrast to myasthenia gravis, where acetylcholine receptor antibodies are often positive, LEMS is characterized by the absence of these antibodies 1. When evaluating a patient with suspected LEMS, the appropriate test to order would be anti-VGCC antibodies rather than acetylcholine receptor antibodies. Other diagnostic tests that support LEMS include screening for underlying malignancies, particularly small cell lung cancer, which is associated with approximately 1% to 1.6% of LEMS cases 1.
From the Research
Acetylcholine Receptor Antibody Titers in Eaton-Lambert Syndrome
- The studies provided do not directly address the question of acetylcholine receptor antibody titers in Eaton-Lambert syndrome 2, 3, 4, 5, 6.
- However, it is mentioned that Lambert-Eaton myasthenic syndrome (LEMS) is an autoimmune disorder caused by antibodies directed against the voltage-gated calcium channels that provide the calcium ion flux that triggers acetylcholine release at the neuromuscular junction 3.
- The autoantibodies in LEMS target multiple subunits of voltage-gated Ca2+ channels, including the α(1) and β(3) subunits, which are associated with acetylcholine release 5.
- The primary issue in LEMS is the reduction of functional P/Q-type voltage-gated calcium channels on presynaptic nerve terminals, leading to diminished release of acetylcholine 2, 6.
- There is no direct evidence provided on the positivity of acetylcholine receptor antibody titers in Eaton-Lambert syndrome, but rather on the autoantibodies targeting voltage-gated calcium channels.