Signs and Symptoms
Symptoms of congenital myopathies
Some of the congenital inheritable myopathies cause severe, general muscle weakness that creates problems with basic activities like swallowing and breathing.
Other inheritable myopathies cause episodes of muscle weakness or stiffness that are milder and more localized, and temporary in nature.
Unlike muscular dystrophies, myopathies usually don’t cause muscles to die; instead, they keep them from working properly. Also, myopathies are usually nonprogressive — that is, a myopathy usually doesn’t grow worse over a person’s lifetime. In fact, some children with myopathies gain strength as they grow older.
Finally, some myopathies can give people a listless facial expression, caused by weakness of muscles in the face. Myopathies have no effect on intelligence.
For more on the specific signs and symptoms of each type of myopathy, see the individual disease pages.
The myopathies almost never affect heart muscles directly. However, sometimes they can cause indirect damage to the heart.
In nemaline myopathy and congenital myotubular myopathy, an inadequate oxygen supply to the body during severe bouts of respiratory weakness can lead to heart problems.
People with myopathies can experience a range of adverse reactions to certain anesthetic drugs used during surgery. Although these drugs sometimes just aggravate the myopathy, they also can produce potentially fatal reactions, such as malignant hyperthermia, which refers to a dangerously high increase in body temperature.
Malignant hyperthermia is triggered by certain inhaled anesthetics (like halothane) and certain muscle relaxants (like succinylcholine). These drugs can intensify ion channel defects and boost muscle metabolism — the set of chemical reactions that provides energy to muscle. The increased metabolism raises body temperature and causes excessive contraction and rhabdomyolysis — a process of acute muscle breakdown. The resulting leakage of ions and muscle proteins into the circulatory system can cause life-threatening damage to the heart, lungs and kidneys.
People with central core disease aren’t always susceptible to malignant hyperthermia. Those who are susceptible won’t experience malignant hyperthermia unless they’re exposed to triggering anesthetics. See Medical Management.