| Etiology | Onset (yr) | Gender | Thymus | Course | |
|---|---|---|---|---|---|
| Neonatal myasthenia | Passage of antibodies from myasthenic mother across the placenta | Neonatal | Both genders | Normal | Transient |
| Congenital myasthenia | Congenital end plate pathology; genetic autosomal recessive pattern of inheritance | 0–2 | Male > female | Normal | Nonfluctuating; compatible with long survival |
| Juvenile myasthenia | Autoimmune disorder | 2–20 | Female > male (4:1) | Hyperplasia | Slowly progressive; tendency to relapse and remission |
| Adult myasthenia | Autoimmune disorder | 20–40 | Female > male | Hyperplasia | Maximum severity within 3–5 years |
| Elderly myasthenia | Autoimmune disorder | >40 | Male > female | Thymoma (benign or locally invasive) | Rapid progress; higher mortality rate |