AUTOANTIBODY EVALUATIONS TO EXPEDITE DIAGNOSIS AND TREATMENT

MYASTHENIA GRAVIS & LAMBERT-EATON SYNDROME

N E U R O L O G Y A T M A Y O C L I N I C

M A Y O M E D I C A L L A B O R A T O R I E S . C O M / N E U R O L O G Y

CLINICAL DIAGNOSIS & NEOPLASTIC ACCOMPANIMENTS

MYASTHENIA GRAVISCharacteristic findings are weakness and fatiguability that are improved by rest or anticholinesterase medication. EMG demonstrates decrement in compound muscle action potential (CMAP) during repetitive-motor nerve stimulation. Chest CT or MRI may reveal thymic enlargement, thymoma, or thymic carcinoma.

Other neoplastic accompaniments other than thymoma include gynecological cancers, prostate cancer, breast cancer, bladder cancer, and lung cancer.

LAMBERT-EATON SYNDROMECharacteristic clinical findings include proximal weakness, sometimes including craniofacial involvement. This can be improved by brief exercise. Limited dysautonomia is frequently encountered, and this can include dry mouth and eyes, impaired sweating, and erectile dysfunction. The EMG findings demonstrate baseline CMAP reduction and facilitation of the CMAP after brief exercise or high-frequency nerve stimulation.

Neoplastic accompaniments include small-cell lung carcinoma in about 90% of paraneoplastic cases.

WHAT ARE MYASTHENIA GRAVIS & LAMBERT-EATON SYNDROME?

Myasthenia gravis and Lambert-Eaton syndrome are autoimmune disorders of neuromuscular

transmission caused by antibodies binding to extracellular muscle membranes and ion channels in

nerve, respectively. In myasthenia gravis, antibodies bind to the acetylcholine receptors or the muscle-

specific kinase (MuSK) antibody in the muscle membrane. In Lambert-Eaton syndrome, antibodies bind

to voltage-gated calcium channels in nerve terminals that regulate acetylcholine release.

ALGORITHMIC APPROACH TO DIAGNOSISAutoantibody profiles aid the diagnosis of myasthenia gravis and Lambert-Eaton syndrome. However, characteristic clinical and electrophysiological features are also required for the diagnosis. Seronegativity does not exclude the diagnosis.

Our diagnostic algorithms consist of tests that are always performed, and then additional testing is performed depending on the initial results. The additional testing in that setting involves looking for other antibody markers, which would support a diagnosis of myasthenia gravis or thymoma.

ALGORITHMS AVAILABLE FOR MYASTHENIA GRAVIS & LAMBERT-EATON SYNDROME:} Myasthenia Gravis Evaluation with MuSK Reflex} Myasthenia Gravis: Adult Diagnosis} Myasthenia Gravis: Pediatric Diagnosis} Myasthenia Gravis: Thymoma Diagnosis} Myasthenia Gravis/Lambert-Eaton Syndrome

Diagnosis

Our laboratory-driven algorithms, based on proven Mayo Clinic diagnostic approaches, are available at:mayomedicallaboratories.com/algorithms

C U S T O M E R S E R V I C E F O R C L I N I C A L S P E C I A L I S T S / 8 5 5 - 5 1 6 - 8 4 0 4

M Y A S T H E N I A G R A V I S A N D L A M B E R T - E A T O N S Y N D R O M E

EVALUATIONS AVAILABLE} Myasthenia Gravis Evaluation with MuSK Reflex, Serum (Mayo ID: MGRM)} Myasthenia Gravis (MG) Evaluation, Adult (Mayo ID: MGEA)} Myasthenia Gravis (MG) Evaluation, Pediatric (Mayo ID: MGEP)} Myasthenia Gravis (MG) Evaluation, Thymoma (Mayo ID: MGETH)} Myasthenia Gravis (MG)/Lambert-Eaton Syndrome (LES) Evaluation (Mayo ID: MGLES)

STAND-ALONE TESTING} Acetylcholine Receptor (Muscle AChR) Binding Antibody, Serum (Mayo ID: ARBI)} Striational (Striated Muscle) Antibodies, Serum (Mayo ID: STR)} Muscle-Specific Kinase (MuSK) Autoantibody, Serum (Mayo ID: MUSK)

MYASTHENIA GRAVIS EVALUATIONSANTIBODIES EVALUATED

ACh Receptor (Muscle) Binding Ab • • • • •ACh Receptor (Muscle) Modulating Ab • • • • •

Striational (Striated Muscle) Ab • • • •

MuSK Autoantibody R

AChR Ganglionic Neuronal Ab R R R •CRMP-5 R R R •

GAD65 Ab Assay R R •Neuronal (V-G) K+ Channel Ab R R •

N-Type Calcium Channel Ab •P/Q-Type Calcium Channel Ab (LEMS) •

TAT 3d 3d 3d 3d 3d

Test Code MGEA MGRM MGEP MGLES MGETH

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KEY• Antibody EvaluatedR Reflex-OnlyFollow-up testing is available for individual antibodies using Mayo Test ID: PNEFS and PNEFC

@mayocliniclabs/mayocliniclabsnews.mayomedicallaboratories.commayomedicallaboratories.com

TAP INTO THE EXPERTISE OF MAYO CLINIC

The Mayo Clinic Neuroimmunology Laboratory

was the first to introduce comprehensive

serological evaluations to aid the diagnosis

of neurological autoimmunity. The laboratory

continues to discover and clinically validate novel

autoantibody profiles that inform neurological

decision-making and guide the search for cancer.

The clinical and research activities of the Mayo

Clinic Neuroimmunology Laboratory focus on

autoimmunity affecting the brain, optic nerve,

retina, spinal cord, autonomic and somatic nerves

and muscle. The neuroimmunology laboratory

complements Mayo Clinic’s Autoimmune

Neurology Clinic.

FOR MORE INFORMATION ABOUT AUTOIMMUNE NEUROLOGY TESTINGMayoMedicalLaboratories.com/neurology

LABORATORY DIRECTORS1 SEAN PITTOCK, M.D.2 ANDREW MCKEON, M.D.

CONSULTANTS3 CHRISTOPHER KLEIN, M.D.4 DANIEL LACHANCE, M.D.

NEUROLOGISTS STAFFING THE CLINICAL LABORATORY ARE AVAILABLE FOR CONSULTATION AND ASSISTANCE IN THE INTERPRETATION OF AUTOANTIBODY EVALUATIONS

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