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Test ID MGL1 Myasthenia Gravis (MG)/Lambert-Eaton Syndrome (LES) Evaluation

Useful For

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

Profile Information

Test ID Reporting Name Available Separately Always Performed
MGLEI MG Lambert-Eaton Interpretation, S No Yes
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

Test ID Reporting Name Available Separately Always Performed
CRMWS CRMP-5-IgG Western Blot, S Yes No
GANG AChR Ganglionic Neuronal Ab, S No No

Testing Algorithm

If acetylcholine receptor (AChR) modulating antibodies are ≥90% and striational antibodies are ≥1:120, then 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 Lambert-Eaton syndrome (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 / Paraneoplastic Autoantibody Evaluation, Serum. Testing for a newly recognized alternative antibody of myasthenia gravis (MG) (muscle-specific receptor tyrosine kinase) is indicated when all tests are negative.

 

See Myasthenia Gravis/Lambert Eaton Syndrome Diagnostic Algorithm in Special Instructions.

Method Name

CCN, CCPQ, ARBI, ARMO, GANG: Radioimmunoassay (RIA)

STR: Enzyme Immunoassay (EIA)

Reporting Name

MG/LES Evaluation

Specimen Type

Serum

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, complete, print, and send 1 of the following forms with the specimen:

General Request Form (Supply T239) (http://www.mayomedicallaboratories.com/it-mmfiles/general-request-form.pdf)

Neurology Test Request Form (T732) (http://www.mayomedicallaboratories.com/media/customer-service/forms/neurology-request-form.pdf)

Specimen Minimum Volume

2 mL

Specimen Stability Information

Specimen Type Temperature Time
Serum Refrigerated (preferred) 28 days
  Frozen  28 days
  Ambient  72 hours

Clinical Information

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 / 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).

 

Note: Single antibody tests may be requested in the follow-up of patients with positive results previously documented in this laboratory.

 

See Myasthenia Gravis/Lambert Eaton Syndrome Diagnostic Algorithm in Special Instructions.

Reference Values

ACh RECEPTOR (MUSCLE) BINDING ANTIBODY

≤0.02 nmol/L

 

ACh RECEPTOR (MUSCLE) MODULATING ANTIBODIES

0-20% (reported as __% loss of AChR)

 

N-TYPE CALCIUM CHANNEL ANTIBODY

≤0.03 nmol/L

 

P/Q-TYPE CALCIUM CHANNEL ANTIBODY

≤0.02 nmol/L

 

STRIATIONAL (STRIATED MUSCLE) ANTIBODIES

<1:120

Cautions

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.

Day(s) Performed

ACh receptor (muscle) binding antibody: Monday through Friday; 11 a.m., 6 p.m., and 10 p.m.; Saturday; 6 a.m.; Sunday; 6 a.m. and 10 a.m.

ACh receptor (muscle) modulating antibodies: Monday through Thursday; 2 p.m.; Saturday; 8 a.m.

Striational (striated muscle) antibodies: Monday through Friday; 4 a.m. and 3 p.m.; Saturday 6 a.m.

CRMP-5-IgG Western blot: Monday, Wednesday, Friday; 8 a.m.

AChR ganglionic neuronal antibody: Monday through Friday; 11 a.m. and 6 p.m.; Saturday; 6 a.m.; Sunday; 6 a.m.

P/Q-type calcium channel antibody; N-type calcium channel antibody: Monday through  Friday; 6 a.m

Report Available

3 days

Performing Laboratory

Mayo Medical Laboratories in Rochester

CPT Code Information

83519-ACh receptor (muscle) binding antibody

83519-ACh receptor (muscle) modulating antibodies

83519-P/Q-type calcium channel antibody

83519-N-type calcium channel antibody

83520-Striational (striated muscle) antibodies

83519-AChR ganglionic neuronal antibody (if appropriate)

84182-CRMP-5-IgG Western blot (if appropriate)

NY State Approved

Unknown