Isaac's syndrome is an immune-mediated peripheral motor neuron disorder characterized by continuous muscle fiber activity at rest resulting in muscle stiffness, cramps, myokymia, and pseudomyotonia.

A rare neuromuscular disorder with onset usually in late childhood or early adulthood, characterized by intermittent or continuous widespread involuntary muscle contractions; FASCICULATION; hyporeflexia; MUSCLE CRAMP; MUSCLE WEAKNESS; HYPERHIDROSIS; TACHYCARDIA; and MYOKYMIA. Involvement of pharyngeal or laryngeal muscles may interfere with speech and breathing. The continuous motor activity persists during sleep and general anesthesia (distinguishing this condition from STIFF-PERSON SYNDROME). Familial and acquired (primarily autoimmune) forms have been reported. (From Ann NY Acad Sci 1998 May 13;841:482-496; Adams et al., Principles of Neurology, 6th ed, p1491)

Isaacs syndrome is an autoimmune peripheral nerve disorder that causes neuromuscular manifestations, including continuous muscle twitching (myokymia).

Isaacs syndrome is an autoimmune peripheral nerve disorder that causes neuromuscular manifestations, including continuous muscle twitching (myokymia).

Isaacs' syndrome is a rare neuromuscular disorder that is characterized by progressive muscle stiffness; continuously contracting or twitching muscles (myokymia); and diminished reflexes. Signs and symptoms generally develop between ages 15 and 60, with most people experiencing symptoms before age 40. Although the exact underlying cause...