Test ID: MGLES
Myasthenia Gravis (MG)/Lambert-Eaton Syndrome (LES) Evaluation
Secondary ID 
A test code used for billing and in test definitions created prior to November 2011
NY State Approved Indicates the status of NY State approval and if the test is orderable for NY State clients.
Useful For Suggests clinical disorders or settings where the test may be helpful
Confirming the autoimmune basis of a defect in neuromuscular transmission (eg, myasthenia gravis [MG], Lambert-Eaton syndrome [LES])
Distinguishing LES from 2 recognized autoimmune forms of MG
Raising the index of suspicion for cancer, particularly primary lung carcinoma (N-type calcium channel antibody)
Providing a quantitative autoantibody baseline for future comparisons in monitoring a patient's clinical course and response to immunomodulatory treatment
Note: Single antibody tests may be requested in the follow-up of patients with positive results previously documented in this laboratory.
Profile Information A profile is a group of laboratory tests that are ordered and performed together under a single Mayo Test ID. Profile information lists the test performed, inclusive of the test fee, when a profile is ordered and includes reporting names and individual availability.
| Test ID | Reporting Name | Available Separately | Always Performed |
|---|---|---|---|
| CCPQ | P/Q-Type Calcium Channel Ab | No | Yes |
| CCN | N-Type Calcium Channel Ab | No | Yes |
| ARBI | ACh Receptor (Muscle) Binding Ab | Yes | Yes |
| ARMO | ACh Receptor (Muscle) Modulating Ab | No | Yes |
| STR | Striational (Striated Muscle) Ab, S | Yes | Yes |
Reflex Tests Lists test(s) that may or may not be performed, at an additional charge, depending on the result and interpretation of the initial test(s)
| Test ID | Reporting Name | Available Separately | Always Performed |
|---|---|---|---|
| CRMWS | CRMP-5-IgG Western Blot, S | No | No |
| GANG | AChR Ganglionic Neuronal Ab, S | No | No |
Testing Algorithm Delineates situation(s) when tests are added to the initial order. This includes reflex and additional tests.
If AChR modulating antibodies are > or =90% and striational antibodies are > or =1:60, AChR ganglionic neuronal antibody and CRMP-5-IgG Western blot will be performed at an additional charge.
This evaluation is recommended for patients presenting with an acquired defect of neuromuscular transmission in whom the differential diagnosis includes LES. It is not recommended for patients with a past history of, or risk factors for, lung cancer and/or concurrent neurological symptoms/signs not attributable to LES; for those situations, order PAVAL/83380 Paraneoplastic Autoantibody Evaluation, Serum. Testing for a newly recognized alternative antibody of MG (muscle-specific receptor tyrosine kinase) is indicated when all tests are negative.
See Myasthenia Gravis/Lambert Eaton Syndrome Diagnostic Algorithm in Special Instructions.
Special Instructions and Forms Describes specimen collection and preparation information, test algorithms, and other information pertinent to test. Also includes pertinent information and consent forms to be used when requesting a particular test
Method Name A short description of the method used to perform the test
CCN/81184, CCPQ/81185, ARBI/8338, ARMO/83378, GANG/84321: Radioimmunoassay (RIA)
STR/8746: Enzyme Immunoassay (EIA)
CRMWS/83107: Western Blot
Reporting Name A shorter/abbreviated version of the Published Name for a test; an abbreviated test name
Aliases Lists additional common names for a test, as an aid in searching
AChR (Acetylcholine Receptor)
Anti-skeletal Muscle Antibodies
Calcium Channel Blockers
Conotoxin (Receptor) Antibodies
Lambert-Eaton Myasthenic Syndrome (LEMS) Antibodies
Motor End-Plate Antibody
Motor Nerve Terminal Antibodies
Muscle Culture Antibodies
Muscle End-Plate Antibodies
Myasthenia Gravis Antibodies
Myoid Antibody
Striational (Striated Muscle) Antibodies
Voltage-Gated Calcium Channel (VGCC) Antibodies
Specimen Type Describes the specimen type needed for testing
Specimen Required Defines the optimal specimen. This field describes the type of specimen required to perform the test and the preferred volume to complete testing. The volume allows automated processing, fastest throughput and, when indicated, repeat or reflex testing.
Container/Tube:
Preferred: Red top
Acceptable: Serum gel
Specimen Volume: 3 mL
Additional Information: Patient should have no general anesthetic or muscle-relaxant drugs in the previous 24 hours.
Forms: If not ordering electronically, submit a General Request Form (Supply T239) with the specimen.
Specimen Minimum Volume Defines the amount of specimen required to perform an assay once, including instrument and container dead space. Submitting the minimum specimen volume makes it impossible to repeat the test or perform confirmatory or perform reflex testing. In some situations, a minimum specimen volume may result in a QNS (quantity not sufficient) result, requiring a second specimen to be collected.
Reject Due To Identifies specimen types and conditions that may cause the specimen to be rejected
| Hemolysis | Mild OK; Gross reject |
| Lipemia | Mild OK; Gross reject |
| Icterus | Mild OK; Gross reject |
| Other | NA |
Specimen Stability Information Provides a description of the temperatures required to transport a specimen to the laboratory. Alternate acceptable temperature(s) are also included.
| Specimen Type | Temperature | Time |
|---|---|---|
| Serum | Refrigerated (preferred) | 14 days |
| Ambient | 72 hours | |
| Frozen | ||
Clinical Information Discusses physiology, pathophysiology, and general clinical aspects, as they relate to a laboratory test
Myasthenia gravis (MG) and Lambert-Eaton syndrome (LES) are acquired disorders of neuromuscular transmission. MG is caused by pathogenic autoantibodies binding to muscle's nicotinic acetylcholine receptor (AChR) or, in a small minority of patients, muscle-specific receptor tyrosine kinase (MuSK); LES 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 LES can affect children (see MGEP/83371 Myasthenia Gravis [MG] Evaluation, Pediatric) as well as adults, although LES is very rare in children. In adults MG is 10 times more frequent than LES, but it is sometimes difficult to distinguish the 2 disorders, clinically and electromyographically. In adults with MG, there is at least a 20% occurrence of thymoma or other neoplasm.
Neoplasms associated with LES or MG are an endogenous source of the antigens driving production of the autoantibodies that characterize each disorder. LES is frequently associated with small-cell lung carcinoma (SCLC). Thus far, MuSK antibody has not been associated with any neoplasm.
Autoimmune serology is indispensable for both the initial evaluation and monitoring of patients with acquired disorders of neuromuscular transmission. The neurological diagnosis depends on the clinical context and electromyographic findings, and is confirmed more readily by a serological profile than by any single test.
Not all of the antibodies in this profile impair neuromuscular transmission (eg, N-type calcium channel antibodies, antibodies directed at cytoplasmic epitopes accessible in detergent solubilized P/Q-type calcium channels and muscle AChRs, or antibodies against sarcomeric proteins that constitute the striational antigens).
See Myasthenia Gravis/Lambert Eaton Syndrome Diagnostic Algorithm in Special Instructions.
Reference Values Describes reference intervals and additional information for interpretation of test results. May include intervals based on age and sex when appropriate. Intervals are Mayo-derived, unless otherwise designated. If an interpretive report is provided, the reference value field will state this.
ACh RECEPTOR (MUSCLE) BINDING ANTIBODY
< or =0.02 nmol/L
ACh RECEPTOR (MUSCLE) MODULATING ANTIBODIES
0-20% (reported as __% loss of AChR)
N-TYPE CALCIUM CHANNEL ANTIBODY
< or =0.03 nmol/L
P/Q-TYPE CALCIUM CHANNEL ANTIBODY
< or =0.02 nmol/L
STRIATIONAL (STRIATED MUSCLE) ANTIBODIES
<1:60
Interpretation Provides information to assist in interpretation of the test results
A patient's autoantibody profile is more informative than the result of any single test for supporting a diagnosis of Myasthenia Gravis (MG) or Lambert-Eaton syndrome (LES), and for predicting the likelihood of lung carcinoma. Muscle acetylcholine receptor (AChR) and striational antibodies are characteristic but not diagnostic of MG. One or both are found in 13% of patients with LES, but calcium channel antibodies are not found in MG (with exception of rare non-thymomatous paraneoplastic cases).
Muscle AChR binding antibody is found in 90% of nonimmunosuppressed MG patients who have thymoma, and 80% have a striational antibody. Calcium channel antibodies have not been encountered with thymoma. The likelihood of thymoma is greatest when striational antibody is accompanied by a high muscle AChR modulating antibody value (> or =90% AChR loss). Detection of CRMP-5-IgG also is consistent with thymoma in patients not at risk for lung carcinoma.
N-type calcium channel antibodies are more highly associated with primary lung cancer than P/Q-type. One or all of the autoantibodies in the MG/LES evaluation can occur with neoplasia without evidence of neurological impairment. Calcium channel antibodies may disappear soon after commencing immunosuppressant therapy. Other serological markers of lung cancer also may disappear.
One or both calcium channel antibodies (P/Q and N) can occur with paraneoplastic and idiopathic cerebellar ataxia, encephalomyeloneuropathies, and autonomic neuropathy.
Titers are generally higher in patients with severe weakness, but severity cannot be predicted by antibody titer.
AChR and striational 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 LES onset. Only about 5% of nonimmunosuppressed adult patients with generalized MG remain seronegative for muscle AChR and striational autoantibodies beyond 12 months.
The alternative muscle autoantigen, MuSK, accounts for approximately 1/3 of seronegative MG cases with predominantly oculobulbar symptoms.
Cautions Discusses conditions that may cause diagnostic confusion, including improper specimen collection and handling, inappropriate test selection, and interfering substances
Antibodies may disappear with immunosuppressant therapy; the neurological diagnosis is further confounded if steroid myopathy develops.
Unexplainable positive muscle acetylcholine receptor (AChR) or striational antibody values occur in 40% of patients with autoimmune liver disorders, approximately 10% of patients with lung cancer, and in patients with graft-versus-host disease and recipients of D-penicillamine.
Low false-positive values for calcium channel antibodies may occur with hypergammaglobulinemia.
In this laboratory, false-positive results for AChR binding antibodies are excluded by routinely retesting positive sera with (125)I-alpha-bungarotoxin in the absence of muscle AChR. False-positive results are most frequent in the bioassay for AChR modulating antibodies; serum redraw will be requested when only this assay yields a positive result. Curare-like drugs used during general anesthesia can yield transient false-positive AChR modulating antibody results.
Seropositive rates differ in different laboratories.
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 one week and assayed if sufficiently decayed, or canceled if radioactivity remains.
Clinical Reference Provides recommendations for further in-depth reading of a clinical nature
1. Lennon VA: Serological profile of myasthenia gravis and distinction from the Lambert-Eaton myasthenic syndrome. Neurology 1997;48(Suppl 5):S23-S27
2. Harper CM, Lennon VA: Lambert-Eaton syndrome. In Current Clinical Neurology: Myasthenia Gravis and Related Disorders. Edited by HJ Kaminski. Totowa, NJ, Humana Press, 2007, (in press)
3. Hoch W, McConville J, Helms S, et al: Auto-antibodies to the receptor tyrosine kinase MuSK in patients with myasthenia gravis without acetylcholine receptor antibodies. Nat Med 2001 Mar;7(3):365-368
Method Description Describes how the test is performed and provides a method-specific reference
Calcium channel binding antibodies (IgG and IgM) are measured quantitatively by immunoprecipitation assays. Selective high-affinity ligands labeled with (125)I are complexed with cation channel proteins detergent-solubilized from membranes of pig cerebral cortical synaptic membranes; omega conopeptide GVIA identifies neuronal N-type Ca(++) channels; omega conopeptide MVIIC identifies neuronal P/Q-type Ca(++) channels; (125)I -alpha-bungarotoxin identifies muscle AChR solubilized from a mixture of innervated and denervated human skeletal muscle. AChR modulating antibody is detected in a bioassay: following 14 hours of incubation with patient's serum, viable, noninnervated, monolayer cultures of human muscle cells are probed with (125)I-bungarotoxin to quantitate percent loss of surface AChR. Striational antibodies (IgG, IgM, and IgA) are detected by EIA using as antigen a mixture of sarcomeric proteins extracted from healthy adult rat skeletal muscle.(Griesmann GE, Kryzer TJ, Lennon VA: Autoantibody profiles of myasthenia gravis and Lambert-Eaton myasthenic syndrome. In Manual of Clinical and Laboratory Immunology. Sixth edition. Edited by NR Rose, RG Hamilton, B Detrick. Washington, DC, ASM Press, 2002, pp 1005-1012)
Day(s) and Time(s) Test Performed Outlines the days and times the test is performed. This field reflects the day and time the sample must be in the testing laboratory to begin the testing process and includes any specimen preparation and processing time required before the test is performed. Some tests are listed as continuously performed, which means assays are performed several times during the day.
P/Q-type calcium channel antibody: Monday, Wednesday, Friday; 6 a.m.
N-type calcium channel antibody: Monday, Wednesday, Friday; 6 a.m..
ACh receptor (muscle) binding antibody: Monday through Thursday; 6 p.m., Saturday; 10 a.m.
ACh receptor (muscle) modulating antibodies: Monday through Thursday; 11 a.m.
Striational (striated muscle) antibodies: Monday through Thursday, Sunday; 10:30 p.m.
CRMP-5-IgG Western blot: Monday through Friday; 6 a.m.
AChR ganglionic neuronal antibody: Tuesday, Thursday, Sunday; 6 a.m.
Analytic Time Defines the amount of time it takes the laboratory to setup and perform the test. This is defined in number of days. The shortest interval of time expressed is "same day/1 day," which means the results may be available the same day that the sample is received in the testing laboratory. One day means results are available 1 day after the sample is received in the laboratory.
Maximum Laboratory Time Defines the maximum time from specimen receipt at Mayo Medical Laboratories until the release of the test result
Specimen Retention Time Outlines the length of time after testing that a specimen is kept in the laboratory before it is discarded
Performing Laboratory Location The location of the laboratory that performs the test
Test Classification Provides information regarding the medical device classification for laboratory test kits and reagents. Tests may be classified as cleared or approved by the US Food and Drug Administration (FDA) and used per manufacturer's instructions, or as products that do not undergo full FDA review and approval, and are then labeled as an Analyte Specific Reagent (ASR), Investigation Use Only (IUO) product, or a Research Use Only (RUO) product.
CPT Code Information Provides guidance in determining the appropriate Current Procedural Terminology (CPT) code(s) information for each test or profile. The listed CPT codes reflect Mayo Medical Laboratories interpretation of CPT coding requirements. It is the responsibility of each laboratory to determine correct CPT codes to use for billing.
83519-59-ACh receptor (muscle) binding antibody
83519-59-ACh receptor (muscle) modulating antibodies
83519-59-P/Q-type calcium channel antibody
83519-59-N-type calcium channel antibody
83520-Striational (striated muscle) antibodies
83519-59-AChR ganglionic neuronal antibody (if appropriate)
84182-CRMP-5-IgG Western blot (if appropriate)
LOINC® Code Information Provides guidance in determining the Logical Observation Identifiers Names and Codes (LOINC) values for the result codes returned for this test or profile.
| Result ID | Reporting Name | LOINC Code |
|---|---|---|
| 8338 | ACh Receptor (Muscle) Binding Ab | 11034-6 |
| 8879 | ACh Receptor (Muscle) Modulating Ab | 30192-9 |
| 81184 | N-Type Calcium Channel Ab | 33979-6 |
| 81185 | P/Q-Type Calcium Channel Ab | 33980-4 |
| 8746 | Striational (Striated Muscle) Ab, S | 8097-8 |
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