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Test ID MGP1 Myasthenia Gravis (MG) Evaluation, Pediatric

Useful For

Recommended for initial investigation of patients presenting at less than age 20 with a defect of neuromuscular transmission

 

Confirming that a recently acquired neurological disorder has an autoimmune basis

 

Distinguishing acquired myasthenia gravis from congenital myasthenic syndromes (persistently seronegative)

 

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

Profile Information

Test ID Reporting Name Available Separately Always Performed
MGEPI MG Pediatric Interpretation, S No Yes
ARBI ACh Receptor (Muscle) Binding Ab Yes Yes
ARMO ACh Receptor (Muscle) Modulating Ab No Yes

Testing Algorithm

See Myasthenia Gravis: Pediatric Diagnostic Algorithm in Special Instructions.

Method Name

Radioimmunoassay (RIA)

Reporting Name

MG Eval, Pediatric

Specimen Type

Serum


Specimen Required


Container/Tube: 

Preferred: Red top

Acceptable: Serum gel

Specimen Volume: 2 mL

Additional Information: Patient should have no general anesthetic or muscle-relaxant drugs in the previous 24 hours.


Specimen Minimum Volume

1.5 mL

Specimen Stability Information

Specimen Type Temperature Time
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 about 3% of cases the pathogenic antibody is directed at the functionally associated muscle-specific receptor tyrosine kinase (MuSK). The outcome is a critical loss of the AChR channel protein, which is required to activate the muscle action potential.

 

Amongst North American Caucasian children (ie, aged 1-18), MG affects prepubertal boys and girls with equal frequency. Spontaneous remissions are relatively frequent. Females predominate (4.5:1) after puberty. Amongst black children with MG, females predominate (2:1) in all age groups, and remissions are infrequent, regardless of therapy.

 

Congenital MG is a hereditary nonautoimmune disorder characterized by defects In AChR or other synaptic proteins.

 

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

 

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

 

See Myasthenia Gravis: Pediatric 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)

Interpretation

Muscle acetylcholine receptor (AChR) autoantibodies are characteristic but not diagnostic of myasthenia gravis (MG). They are found in 13% of patients with Lambert-Eaton Syndrome (LES), which is rare in children. The patient's autoantibody profile is more informative than the result of any single test for supporting a diagnosis of MG.

 

Titers of AChR antibodies are generally higher in patients with severe weakness, but severity cannot be predicted by antibody titer. Seronegativity is more frequent in children with prepubertal onset of acquired MG (33%-50%) than in adults (<10%). Thymoma is rare under age 20, and striational antibodies (see STR / Striational [Striated Muscle] Antibodies, Serum) also are rare, except in the context of MG related to neoplasia (usually thymoma or neuroblastoma), graft-versus-host disease, autoimmune liver disease, or D-penicillamine therapy. This laboratory has recently noted muscle-specific receptor tyrosine kinase antibody in children with "seronegative" acquired MG, but the frequency of this antibody in pediatric MG has not been determined.

Clinical Reference

1. Andrews PI, Massey JM, Howard JF Jr, Sanders DB: Race, sex, and puberty influence onset, severity, and outcome in juvenile myasthenia gravis. Neurology 1994 July;44(7):1208-1214

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

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. Joshi DD, Anderson PM, Matsumoto J, et al: Metastatic chondroblastoma with elevated creatine kinase and paraneoplastic neurologic autoimmunity. J Pediatr Hematol Oncol 2003;25:900-904

Day(s) and Time(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.

Analytic Time

3 days

Test Classification

See individual components

CPT Code Information

83519-ACh receptor (muscle) binding antibody

83519-ACh receptor (muscle) modulating antibodies

LOINC Code Information

Test ID Test Order Name Order LOINC Value
MGP1 MG Eval, Pediatric 53705-0

 

Result ID Test Result Name Result LOINC Value
8338 ACh Receptor (Muscle) Binding Ab 11034-6
8879 ACh Receptor (Muscle) Modulating Ab 30192-9
34275 MG Pediatric Interpretation, S 69048-7

Forms

If not ordering electronically, complete, print, and send a Neurology Specialty Testing Client Test Request (T732) with the specimen (http://www.mayomedicallaboratories.com/it-mmfiles/neurology-request-form.pdf)