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Test ID: MGT1 Myasthenia Gravis (MG) Evaluation, Thymoma, Serum

Useful For

Investigating patients with suspected or proven thymoma, whether or not symptoms or signs of myasthenia gravis (MG) are present

 

Serially monitoring patients for recurrence or metastasis after removal of thymoma

 

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

 

Assessing the likelihood of occult thymoma in a patient with an acquired disorder of neuromuscular or autonomic transmission

 

Evaluating bone marrow transplant recipients with suspected graft-versus-host disease, particularly if there is evidence of weakness

 

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

Profile Information

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

Testing Algorithm

Recommended for investigation of: 1) a patient with suspected or proven thymoma, whether or not symptoms or signs of myasthenia gravis (MG) are present (also of value for serially monitoring patients after removal of thymoma; a rising autoantibody titer may herald tumor persistence or recurrence), or emergence of an unrelated neoplasm and 2) a bone marrow transplant recipient with suspected graft-versus-host disease, particularly if there is evidence of weakness.

 

See Myasthenia Gravis: Thymoma Diagnostic Algorithm in Special Instructions.

Method Name

ARBI, ARMO, GANG, GD65S, VGKC: Radioimmunoassay (RIA)

STR: Enzyme Immunoassay (EIA)

CRMWS: Western Blot

Reporting Name

MG Evaluation, Thymoma

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). Synaptic transmission fails when these pathogenic autoantibodies cause a critical loss of the AChR cation channel protein, which is required to activate the muscle action potential.

 

It is estimated that approximately 20% of adult patients have a paraneoplastic basis for MG. Thymoma is the most common neoplasm, often occult at the onset of MG, its diagnosis may precede MG onset. Thymoma is thought to be an endogenous source of muscle and neuronal antigens that drive production of characteristic autoantibodies. Other autoimmune neurological disorders sometimes accompany thymoma, with and without MG, including neuromuscular hyperexcitability, autonomic neuropathy, especially gastrointestinal dysmotilities encephalopathy, subacute hearing loss, or polymyositis.

 

MG can affect children as well as adults, but a paraneoplastic context is rare in children (neuroblastoma or thymoma are sometimes found).

 

Some of the antibodies in this profile are not pathogenic (eg, antibodies directed at cytoplasmic epitopes accessible in solubilized ion channels, or sarcomeric proteins that constitute the striational antigens).

 

Autoimmune serology is indispensable for initial evaluation and monitoring the course of patients with acquired MG. The neurological diagnosis depends on the clinical context, electromyographic findings, and response to anticholinesterase administration. MG is confirmed more readily by the individual patient's serological profile than by any single test.

 

See Myasthenia Gravis: Thymoma 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)

 

STRIATIONAL (STRIATED MUSCLE) ANTIBODIES

<1:120

 

CRMP-5-IgG WESTERN BLOT

Negative

 

AChR GANGLIONIC NEURONAL ANTIBODY

≤0.02 nmol/L

 

NEURONAL (V-G) K+ CHANNEL AUTOANTIBODY

≤0.02 nmol/L

 

GAD65 ANTIBODY ASSAY

≤0.02 nmol/L

Interpretation

A patient's autoantibody profile is more informative than the result of any single test for predicting the likelihood of thymoma, and for supporting a diagnosis of myasthenia gravis (MG) or other paraneoplastic neurological complication.

 

Muscle acetylcholine receptor (AChR) and striational autoantibodies are characteristic but not diagnostic of MG in the context of thymoma. One or more antibodies in the MG/thymoma evaluation are positive in more than 60% of nonimmunosuppressed patients who have thymoma without evidence of any neurological disorder.

 

Titers of muscle AChR and striational antibodies are generally higher in MG patients who have thymoma, but severity of weakness cannot be predicted by antibody titer. A rising antibody titer (or appearance of a new antibody specificity) following thymoma ablation suggests thymoma recurrence or metastasis, or development of an unrelated neoplasm.

 

Antibodies specific for the alternative muscle autoantigen of MG, muscle-specific receptor tyrosine kinase, are not associated with thymoma.

Clinical Reference

1. Cikes N, Momoi MY, Williams CL, et al: Striational autoantibodies: quantitative detection by enzyme immunoassay in myasthenia gravis, thymoma and recipients of D-penicillamine and allogenic bone marrow. Mayo Clin Proc 1988 May;63(5):474-481

2. Lennon VA: Serological profile of myasthenia gravis and distinction from the Lambert-Eaton myasthenic syndrome. Neurology 1997;48(Suppl 5):S23-S27

3. Vernino S, Lennon VA: Autoantibody profiles and neurological correlations of thymoma. Clin Can Res 2004;10:7270-7275

4. 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

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

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 (V-G) K+ channel 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

LOINC Code Information

Test ID Test Order Name Order LOINC Value
MGT1 MG Evaluation, Thymoma 90231-2

 

Result ID Test Result Name Result LOINC Value
8338 ACh Receptor (Muscle) Binding Ab 11034-6
8879 ACh Receptor (Muscle) Modulating Ab 30192-9
83107 CRMP-5-IgG Western Blot, S 47401-5
84321 AChR Ganglionic Neuronal Ab, S 94694-7
81596 GAD65 Ab Assay, S 94345-6
8746 Striational (Striated Muscle) Ab, S 94817-4
89165 Neuronal (V-G) K+ Channel Ab, S 94816-6
34274 MG Thymoma Interpretation, S 69048-7

CPT Code Information

83519 x 4-ACh receptor (muscle) binding antibody

83520

84182

86341

Forms

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

Mayo Clinic Laboratories | Neurology Catalog Additional Information:

mml-neuroimmunology