Myasthenia Gravis: Test and Diagnosis

1st order laboratory parameters – obligatory laboratory tests.

• Small blood count
• Differential blood count
• Electrolytes – calcium, magnesium, sodium, potassium, phosphates, chloride.
• Inflammatory parameters – CRP (C-reactive protein) or ESR (erythrocyte sedimentation rate).
• Liver parameters – alanine aminotransferase (GPT), aspartate aminotransferase (GOT).
• Fasting glucose (fasting blood glucose), if necessary oral glucose tolerance test (oGTT).
• Thyroid parameters – TSH, fT3, fT4
• Serum protein and immunoelectrophoresis.
• Vitamin B12 (methylmalonic acid, homocysteine)
• Autoantibody diagnostics:
  • Anti-AChR-AK – positive at:
    • Approximately 50% of patients with ocular (affecting the eyes) myasthenia gravis.
    • Up to 90% of patients with generalized (affecting the entire body) myasthenia gravis; 10-20% of patients with generalized myasthenia gravis do not have detectable anti-AChR AKs
    • Nearly 100% of patients with paraneoplastic myasthenia with thymoma (tumor arising from thymic tissue)
  • Anti-AChR-Ak
    • May also be detectable in individual patients with thymoma who do not clinically have myasthenia at the time of surgery but may develop it during the course (“post-thymomectomy myasthenia”)
    • Other patients with thymoma with clinical myasthenia at the time of surgery only develop anti-AChR-Ak during the course.
  • Anti-titin AK
    • Are the correlate of auto-Ak against skeletal muscle, which is frequently associated with thymoma in patients < 60 years of age
    • In patients > 60 years of age, an increase in anti-titin AK is often without disease significance
  • Anti-MuSK-AK
    • Antibodies against muscle-specific tyrosine kinase (MuSK) can be detected in 1-10% of cases.

Laboratory parameters 2nd order – depending on the results of the history, physical examination and mandatory laboratory parameters – for differential diagnostic clarification.

• Anti-VGCC-AK (voltage-gated calcium channels; VGCC; positive in up to 90% with Lambert-Eaton syndrome) – rarely, myasthenia is combined with Lambert-Eaton syndrome with AChR and VGCC antibodies.
• Screening for concomitant autoimmune diseases (see each with the corresponding disease).
  • Ulcerative colitis (inflammatory bowel disease (IBD))
  • Glomerulonephritis (inflammation of the glomeruli (renal corpuscles) of the kidneys).
  • Crohn’s disease (inflammatory bowel disease (IBD))
  • Pemphigus vulgaris (blistering skin disease).
  • Pernicious anemia (absorption disorder for B12; B12 deficiency anemia).
  • Rheumatoid arthritis (common) – CRP (C-reactive protein) or ESR (erythrocyte sedimentation rate); rheumatoid factor (RF), CCP-AK (cyclic citrulline peptide antibodies), ANA* (antinuclear antibodies).
  • Ankylosing spondylitis (synonym: ankylosing spondylitis; chronic inflammatory rheumatic disease with pain and stiffening of joints).
  • Systemic lupus erythematosus – lupus anticoagulant.
  • Thyroiditis (inflammation of the thyroid gland) (common).
• CSF puncture (collection of cerebrospinal fluid by puncture of the spinal canal) for CSF diagnosis – exclusion/detection of inflammatory CNS diseases.
• Muscle biopsy (tissue sample of a muscle) in the area of the end plate – exclusion / detection of myopathy (diseases of the muscles) or mitochondrial disease.

Pharmacological tests

Edrophonium test (formerly: tensilon test).

Intravenous application of edrophonium (fractionated administration of 2 + 3 + 5 mg in adults, fractionated administration of 2-3 x 0.02 mg/kg bw in children) results in improvement of symptoms within 30-60 seconds if positive. Photo documentation (before/after) is recommended.The antidote atropine (0.5-1.0 mg) should be ready and administered immediately in case of pronounced muscarinic side effects such as bradycardia (excessively slow heartbeat: < 60 beats per minute), hypotonic circulatory response, bronchospasm (bronchial spasm).The edrophonium test should not be performed in the outpatient clinic because of the risk of asystole (cardiac arrest)! Other contraindications are bradycardic arrhythmias and bronchial asthma. (Risk-benefit analysis!) Neostigmine test

The effect occurs only after a few minutes and lasts for over an hour.The test is performed when symptom assessment is difficult, such as in cases of psychogenic superimposition or dissociative symptom patterns.