There are several conditions that affect the neuromuscular junction. Below we have provided brief information on some of these disorders. As every condition is different, it is important that you consult with your doctor or health professional concerning your particular diagnosis and treatment plan.
Autoimmune myasthenia gravis: This is the most common form of MG, characterized by fluctuating weakness of the voluntary muscle groups. In autoimmune MG, the immune system mistakenly attacks and destroys the body’s own tissues by forming autoantibodies.
Congenital myasthenic syndromes (CMS): This term is reserved for a group of uncommon, hereditary disorders of the neuromuscular junction. There are many different types of CMS, each the result of a genetic mutation in a specific protein component of the neuromuscular junction. A thorough diagnostic evaluation is worthwhile in patients with suspected CMS because of the different types and different treatment options.
What is the difference between CMS and autoimmune MG?
- CMS is rarer than autoimmune MG.
- CMS usually manifests early in life, often in infancy.
- CMS symptoms tend to be lifelong and/or relatively stable with generalized fatigue and weakness, with less frequent or less significant exacerbations.
- CMS is not associated with antibodies against the components of the neuromuscular junction.
- All CMS disorders result from genetic mutations in components of the neuromuscular junction.
- CMS symptoms do not require immunotherapy.
Transient neonatal myasthenia: This disorder occurs in 10-15% of infants born to mothers with autoimmune MG. Maternal antibodies that cross the placenta in late pregnancy cause transient neonatal myasthenia. Symptoms include a weak cry or suck and generalized weakness at birth. As the maternal antibodies degrade in infant’s body, symptoms gradually disappear within a few weeks. Infants with transient neonatal myasthenia gravis do not have an increased risk for long-term or future MG.
To learn more, see information from Andrew G. Engel, MD, courtesy of the National Organization for Rare Disorders
Lambert-Eaton Myasthenic Syndrome (LEMS)*: This is another autoimmune disease in which the immune system attacks the body’s own neuromuscular junction. Different from autoimmune MG in which the autoimmune system attacks the muscle aspect of the neuromuscular junction, LEMS is caused by autoimmune attacks to the nerve aspect, interfering with the ability of nerve cells to send signals to muscle fibers.
There are two forms of LEMS:
- One form (50-60% of cases) is associated with small cell lung cancer and has an older age of onset.
- The other form (40-50% of cases) is not associated with cancer and has a younger age of onset.
* Information is courtesy of the Muscular Dystrophy Association