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Test ID: MGA1 Myasthenia Gravis (MG) Evaluation, Adult, Serum

Useful For

Initial evaluation of patients aged 20 or older with symptoms and signs of acquired myasthenia gravis (MG)

 

Bone marrow transplant recipients with suspected graft-versus-host disease, particularly if weakness has appeared

 

Confirming that a recently acquired neurological disorder has an autoimmune basis (eg, MG)

 

Providing a quantitative baseline for future comparisons in monitoring a patient's clinical course and the response to immunomodulatory treatment

 

Raising likelihood of neoplasia

Profile Information

Test ID Reporting Name Available Separately Always Performed
MGEAI MG Adult Interpretation, S 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
GD65S GAD65 Ab Assay, S Yes No
CRMWS CRMP-5-IgG Western Blot, S Yes No
GANG AChR Ganglionic Neuronal Ab, S No No
VGKC Neuronal (V-G) K+ Channel Ab, S No No

Testing Algorithm

If acetylcholine receptor (AChR) modulating antibodies are ≥90% and striational antibodies are ≥1:120, then AChR ganglionic neuronal autoantibody, glutamic acid decarboxylase autoantibody, neuronal voltage-gated potassium channel autoantibody, and CRMP-5-IgG Western blot will be performed at an additional charge.

 

See Myasthenia Gravis: Adult Diagnostic Algorithm in Special Instructions.

Method Name

ARBI, ARMO, GANG, VGKC: Radioimmunoassay (RIA)

STR: Enzyme Immunoassay (EIA)

Reporting Name

MG Evaluation, Adult

Specimen Type

Serum


Specimen Required


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.


Specimen 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) is an acquired disorder of neuromuscular transmission caused by the binding of pathogenic autoantibodies to muscle's postsynaptic nicotinic acetylcholine receptor (AChR). In a small minority of patients the pathogenic antibody is directed at the muscle-specific receptor tyrosine kinase (MuSK) antigen. The ensuing weakness in both cases reflects a critical loss of the AChR channel protein, which is required to activate the muscle action potential.

 

MG affects children (see MGP1 / Myasthenia Gravis [MG] Evaluation, Pediatric) as well as adults. In adults with MG there is at least a 20% occurrence of thymoma or other neoplasm. Neoplasms are an endogenous source of the antigens driving production of autoantibodies.

 

Autoimmune serology is indispensable for 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 the individual patient's serological profile than by any single test.

 

Not all of the antibodies detected in this profile impair neuromuscular transmission (eg, antibodies directed at cytoplasmic epitopes accessible on solubilized AChR, or sarcomeric proteins that constitute the striational antigens).

 

If muscle acetylcholine receptor (AChR) modulating antibody value is (or exceeds) 90% AChR loss and striational antibody is detected, thymoma is likely. Reflexive testing will include collapsin response-mediated protein-5-lgG Western blot, ganglionic AChR antibody, glutamic acid decarboxylase (GAD65) antibody, and voltage-gated potassium channel complex (VGKC) antibody (which are frequent with thymoma).

 

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

 

See Myasthenia Gravis: Adult Diagnostic Algorithm in Special Instructions.

Interpretation

The patient's autoantibody profile is more informative than the result of any single test for supporting a diagnosis of myasthenia gravis (MG), and for predicting the likelihood of thymoma (see MGT1 / Myasthenia Gravis [MG] Evaluation, Thymoma).

 

Muscle acetylcholine receptor (AChR) and striational autoantibodies are characteristic but not diagnostic of MG. One or both are found in 13% of patients with Lambert-Eaton Syndrome (LES), but P/Q-type calcium channel autoantibodies are very rare in MG.

 

Results are sometimes positive in patients with neoplasia without evidence of neurological impairment.

 

Titers are generally higher in patients with severe weakness, or with thymoma, but severity cannot be predicted by antibody titer.

 

Test results for muscle acetylcholine receptor and striational antibodies may be negative for 6 to 12 months after MG symptom onset. Only 8% of nonimmunosuppressed patients with generalized MG remain seronegative beyond 12 months for all autoantibodies in the adult MG evaluation. Of those patients 38% will have the alternative muscle-specific receptor tyrosine kinase (MuSK)-specific autoantibody.

 

MuSK antibody-positive patients lack thymoma, and have predominantly oculobulbar symptoms that respond to plasmapheresis and immunosuppressant therapy. They do not benefit from thymectomy.

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

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, 2002, pp 269-291

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

4. Chan KH, Lachance DH, Harper CM, Lennon VA: Frequency of seronegativity in adult-acquired generalized myasthenia gravis. Muscle Nerve 2007;36:651-658

5. Skjei KL, Lennon VA, Kuntz NL: Muscle specific kinase antibody-associated myasthenia gravis in children; clinical, serologic, electrophysiologic and pathologic characteristics and response to treatment. Ann Neurol 62(S11):S145-S146

Day(s) and Time(s) Performed

ACh receptor (muscle) binding antibody:

Monday through Friday; 11 a.m., 6 p.m., 10 p.m.

Saturday; 6 a.m.

Sunday; 6 a.m., 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., 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., 6 p.m.

Saturday; 6 a.m.

Sunday; 6 a.m.

 

Neuronal VGKC autoantibody:

Monday through Friday; 11 a.m., 6 p.m.

Saturday; 6 a.m.

Sunday; 6 a.m.

 

GAD65 antibody assay:

Monday through Friday; 6 a.m., 4 p.m.

Analytic Time

3 days

CPT Code Information

83519 x 2

83520

83519 x 2 (if appropriate)

84182 (if appropriate)

86341 (if appropriate)

LOINC Code Information

Test ID Test Order Name Order LOINC Value
MGA1 MG Evaluation, Adult 53706-8

 

Result ID Test Result Name Result LOINC Value
34272 MG Adult Interpretation, S 69048-7
8338 ACh Receptor (Muscle) Binding Ab 11034-6
8879 ACh Receptor (Muscle) Modulating Ab 30192-9
8746 Striational (Striated Muscle) Ab, S 94817-4

Reference Values

ACh RECEPTOR (MUSCLE) BINDING ANTIBODY

≤0.02 nmol/L

 

ACh RECEPTOR (MUSCLE) MODULATING ANTIBODIES

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

 

STRIATIONAL (STRIATED MUSCLE) ANTIBODIES

<1:120

Forms

If not ordering electronically, complete, print, and send a Neurology Specialty Testing Client Test Request (T732) with the specimen.

Test Classification

This test was developed and its performance characteristics determined by Mayo Clinic in a manner consistent with CLIA requirements. This test has not been cleared or approved by the U.S. Food and Drug Administration.
Mayo Clinic Laboratories | Neurology Catalog Additional Information:

mml-neuroimmunology