Isaac's syndrome (also known as neuromyotonia, Isaac-Mertens syndrome, continuous muscle fiber activity syndrome, and quantal squander syndrome) is a rare neuromuscular disorder caused by continuous signaling of the end regions of peripheral nerve fibers that activate muscle fibers (motor neurons). Symptoms, which include progressive muscle stiffness, continuous vibrating or twitching muscles, cramping, increased sweating, and delayed muscle relaxation, occur even during sleep or when patients are under general anesthesia. Many patients develop weakened reflexes and muscle pain, but numbness is relatively uncommon. Although symptoms can be limited to cranial muscles, in most patients stiffness is most prominent in limb and trunk muscles. Speech and breathing may be affected if pharyngeal or laryngeal muscles are involved. Age of onset is between ages 15 and 60, with most patients experiencing symptoms before age 40. There are hereditary and acquired forms of the disorder. The acquired form may develop in association with peripheral neuropathies or as an autoimmune condition.
National Organization for Rare Disorders (NORD) P.O. Box 1968 (55 Kenosia Avenue) Danbury, CT 06813-1968 orphan@rarediseases.org http://www.rarediseases.org Tel: 203-744-0100 Voice Mail 800-999-NORD (6673) Fax: 203-798-2291 |
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Last updated January 14, 2008