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HelpTest ID: MGLE Myasthenia Gravis/Lambert-Eaton Myasthenic Syndrome Evaluation, Serum
Ordering Guidance
This test should not be requested in patients who have recently received radioisotopes, therapeutically or diagnostically, because of potential assay interference. The specific waiting period before specimen collection will depend on the isotope administered, the dose given, and the clearance rate in the individual patient. Specimens will be screened for radioactivity prior to analysis. Radioactive specimens received in the laboratory will be held for 1 week and assayed if sufficiently decayed or canceled if radioactivity remains.
Specimen Required
Patient Preparation: For optimal antibody detection, specimen collection is recommended prior to initiation of immunosuppressant medication.
Supplies: Sarstedt Aliquot Tube, 5 mL (T914)
Collection Container/Tube:
Preferred: Red top
Acceptable: Serum gel
Submission Container/Tube: Plastic vial
Specimen Volume: 3 mL
Collection Instructions: Centrifuge and aliquot serum into a plastic vial.
Useful For
Confirming the autoimmune basis of a defect in neuromuscular transmission (eg, myasthenia gravis [MG], Lambert-Eaton myasthenic syndrome [LEMS])
Distinguishing LEMS from autoimmune forms of MG
Providing a quantitative autoantibody baseline for future comparisons in monitoring a patient's clinical course and response to immunomodulatory treatment
Profile Information
| Test ID | Reporting Name | Available Separately | Always Performed |
|---|---|---|---|
| MGLEI | MG Lambert-Eaton Interpretation, S | No | Yes |
| ARBI | ACh Receptor (Muscle) Binding Ab | Yes | Yes |
| CCPQ | P/Q-Type Calcium Channel Ab | No | Yes |
Reflex Tests
| Test ID | Reporting Name | Available Separately | Always Performed |
|---|---|---|---|
| ACMFS | AChR Modulating Flow Cytometry, S | No | No |
| MUSK | MuSK Autoantibody, S | Yes | No |
Testing Algorithm
If acetylcholine receptor (AChR)-binding antibodies are greater than 0.02 nmol/L, then AChR muscle modulating antibody will be performed at an additional charge.
If AChR-binding antibodies are 0.02 nmol/L or less, then muscle-specific kinase (MuSK) autoantibody will be performed at an additional charge.
If unable to report AChR binding antibody due to interfering substances, then AChR muscle modulating antibody will be performed at an additional charge.
If unable to report AChR binding antibody due to interfering substances and AChR muscle modulating antibody is negative, MuSK autoantibody will be performed at an additional charge.
Method Name
ARBI, CCPQ, MUSK: Radioimmunoassay (RIA)
ACMFS: Flow Cytometry
MGLEI: Medical Interpretation
Reporting Name
MG/LEMS Evaluation, SSpecimen Type
SerumSpecimen Minimum Volume
2 mL
Specimen Stability Information
| Specimen Type | Temperature | Time | Special Container |
|---|---|---|---|
| Serum | Refrigerated (preferred) | 28 days | |
| Frozen | 28 days | ||
| Ambient | 72 hours |
Clinical Information
Myasthenia gravis (MG) and Lambert-Eaton myasthenic syndrome (LEMS) are acquired autoimmune disorders of neuromuscular transmission. MG is caused by pathogenic autoantibodies binding and potentially removing (modulation) the muscle's nicotinic acetylcholine receptor (AChR) from the surface of the neuromuscular junction. Serologically, the detection of AChR binding antibody provides the best diagnostic sensitivity. However, the presence of both AChR binding and modulating activity improves diagnostic accuracy. A subset of patients who are AChR seronegative will have muscle-specific kinase (MuSK) antibodies.
LEMS is caused by autoantibodies binding to motor nerve terminal's voltage-gated P/Q-type calcium channel. Synaptic transmission fails when autoantibodies cause a critical loss of junctional cation channel proteins that activate the muscle action potential.
Both MG and LEMS can affect children as well as adults, although LEMS is very rare in children. In adults MG is 10 times more frequent than LEMS, but it is sometimes difficult to distinguish the two disorders clinically. Electrophysiological testing is extremely helpful in distinguishing these 2 disorders. MG patients have decrements of compound muscle action potential (CMAP) amplitudes on repetitive stimulation whereas LEMS has immediate and dramatic post exercise facilitation (elevation) of CMAP amplitudes. Neoplasms associated with LEMS or MG are an endogenous source of the antigens driving production of the autoantibodies that characterize each disorder. In adults with MG, there is at least a 20% occurrence of thymoma and, very rarely (<1%), extrathymic cancers. LEMS is frequently associated (80%) with small-cell lung carcinoma (SCLC). Thus far, MuSK antibody associated MG has not been associated with any neoplasm.
The diagnostic sensitivity of these tests depends on the disease severity and duration of symptoms. AChR binding antibodies may be undetectable for 6 to 12 months after MG symptom onset and similarly P/Q-type calcium channel antibody may be undetectable for 6 to 12 months after LEMS onset. Only about 5% of adult patients with generalized MG who are not immunosuppressed remain seronegative for muscle AChR beyond 12 months. Although immunotherapy is universally beneficial for MG, in LEMS resection of the identified SCLC and initiation of 3,4-diaminopyridine, which facilitates acetylcholine release by increasing presynaptic calcium concentration, is most beneficial.
Note: Single antibody tests may be requested in the follow-up of patients with positive results previously documented in this laboratory.
Reference Values
|
Test ID |
Reporting name |
Methodology |
Reference value |
|
MGLEI |
MG Lambert-Eaton Interpretation, S |
Interpretation |
NA |
|
ARBI |
ACh Receptor (Muscle) Binding Ab |
Radioimmunoassay (RIA) |
≤0.02 nmol/L |
|
CCPQ |
P/Q-Type Calcium Channel Ab |
RIA |
≤0.02 nmol/L |
Reflex Information:
|
Test ID |
Reporting name |
Methodology |
Reference value |
|
ACMFS |
AChR Modulating Flow Cytometry, S |
Flow cytometry |
Negative |
|
MUSK |
MuSK Autoantibody, S |
RIA |
≤0.02 nmol/L |
Interpretation
Positive results in this antibody evaluation are indicative of an autoimmune neuromuscular junction disorder. These results should be interpreted in the appropriate clinical and electrophysiological context.
In the presence of either acetylcholine receptor antibodies or P/Q antibodies, a paraneoplastic basis should be considered with thymoma being the most commonly associated tumor with myasthenia gravis and small cell lung cancer being the most commonly associated cancer with Lambert-Eaton myasthenic syndrome. Currently, muscle-specific kinase antibody positive myasthenia gravis is not associated with a paraneoplastic etiology.
Negative results do not exclude the diagnosis of an autoimmune neuromuscular junction disorder. If clinical suspicion remains and symptoms persistent or worsen consider retesting.
Clinical Reference
1. Lennon VA. Serological profile of myasthenia gravis and distinction from the Lambert-Eaton myasthenic syndrome. Neurology. 1997;48(Suppl 5):S23-S27. doi:10.1212/WNL.48.Suppl_5.23S
2. Harper CM, Lennon VA: Lambert-Eaton syndrome. In: Kaminski HJ, ed. Current Clinical Neurology: Myasthenia Gravis and Related Disorders. 2nd ed. Humana Press; 2008;209-226
3. Hoch W, McConville J, Helms S, Newsom-Davis J, Melms A, Vincent A. Auto-antibodies to the receptor tyrosine kinase MuSK in patients with myasthenia gravis without acetylcholine receptor antibodies. Nat Med. 2001;7(3):365-368. doi:10.1038/85520
4. Shelly S, Paul P, Bi H, et al. Improving accuracy of myasthenia gravis autoantibody testing by reflex algorithm. Neurology. 2020;95(22):e3002-e3011. doi:10.1212/WNL.0000000000010910
Day(s) Performed
Profile tests: Monday through Sunday; Reflex tests: Varies
Report Available
3 to 10 daysTest Classification
This test was developed and its performance characteristics determined by Mayo Clinic in a manner consistent with CLIA requirements. It has not been cleared or approved by the US Food and Drug Administration.CPT Code Information
86041
86596
86043 (if appropriate)
86366 (if appropriate)
LOINC Code Information
| Test ID | Test Order Name | Order LOINC Value |
|---|---|---|
| MGLE | MG/LEMS Evaluation, S | 97566-4 |
| Result ID | Test Result Name | Result LOINC Value |
|---|---|---|
| 8338 | ACh Receptor (Muscle) Binding Ab | 97558-1 |
| 81185 | P/Q-Type Calcium Channel Ab | 94349-8 |
| 34273 | MG Lambert-Eaton Interpretation, S | 69048-7 |
Forms
If not ordering electronically, complete, print, and send a Neurology Specialty Testing Client Test Request (T732) with the specimen.
mml-Neuromuscular