Isaac's syndrome, also known as neuromyotonia, is a neuromuscular disorder affecting the signaling between nerves and muscles. It is caused by abnormal continuous signaling at the end of peripheral nerve fibers that activate muscle fibers. Symptoms, which include progressive muscle stiffness, continuously contracting or twitching muscles, cramping, increased sweating, and delayed muscle relaxation, occur even during sleep or when individuals are under general anesthesia. Many people also develop weakened reflexes and muscle pain, but numbness is relatively uncommon. In most people with Isaac's syndrome, stiffness is most prominent in limb and trunk muscles, although symptoms can be limited to cranial muscles. Speech and breathing may be affected if pharyngeal or laryngeal muscles are involved.
There are hereditary and acquired (occurring from unknown causes) forms of the disorder. The acquired forms can result from toxic exposure (for instance, to gold or mercury) or from certain tumors located between the neck and the abdomen. They can also occur as an autoimmune disease where the body’s immune system starts to abnormally produce antibodies that target the muscle nerves and thus affect muscle movement.
There is no cure or specific treatment for this disorder. However, treatments for some of the symptoms are available. Treatment is directed at managing the signs and symptoms, and may include Immunosuppressive medications and Anti-seizure medications.
Little research is being done on this disease, so the long-term prognosis for individuals with the disorder is uncertain.