Myasthenia, or myasthenia gravis, is the medical term for muscle weakness. Within this category, there are at least three different sub-categories of myasthenia. However, all relate to nueromuscular disorders. The disorder most commonly shows itself during childhood, though it can happen in adulthood. One dead giveaway for myasthenia is where the muscles will be weak all the time. Facial muscles including muscles that control the eyelids, muscles that move the eyes, and muscles for chewing and swallowing are most commonly affected by myasthenia. However, the skeletal muscles can be affected in this condition. Myasthenia gravis, or MG effects approximately two out of every 100,000 people. In women, MG is most common for women between 18 and 25, while men most commonly contract MG during the ages of 60 - 80 years old.
There are all different kinds of myasthenia, and they include:
- ocular MG - weakness in only the muscles that control eye movement; effects 10-15% of people with MG, the least common type of MG.
- congenital MG - an inherited condition caused by a genetic defect.
- transient neonatal MG - 10-20% development rate in infants whose mothers have MG. A transient neonatal MG is caused by the circulation of their mother's antibodies throughout the placenta and as long as it lasts as long as the mother's antibodies to remain in the infant, usually weeks after birth.