Isaac's syndrome; neuromyotonia; Isaac's-Merten's syndrome; continuous muscle fiber activity syndrome; quantal squander syndrome

Etiology

• acquired form may develop in association with:
  • peripheral neuropathy
  • autoimmune disease

Epidemiology

• rare neuromuscular disorder
• age of onset is between ages 15 and 60, with most patients experiencing symptoms before age 40

Pathology

• continuous signaling of motor neurons
• autoimmune form: antibodies that bind to ion channels on motor nerve fibers

Genetics

• hereditary & acquired forms

Clinical manifestations

• progressive muscle stiffness
• fasciculations
• cramping
• hyperhidrosis
• delayed muscle relaxation
• sign/symptoms occur even during sleep or when patients are under general anesthesia
• hyporeflexia
• myalgias
• numbness is relatively uncommon
• symptoms can be limited to cranial muscles
• in most patients, stiffness is most prominent in limb & trunk muscles
• speech & breathing may be affected if pharyngeal or laryngeal muscles are involved

Management

• anticonvulsants, phenytoin & carbamazepine, usually provide significant relief from the stiffness, muscle spasms, & pain
• plasmapheresis may provide short-term relief for patients autoantibodies
• prognosis
  • no cure
  • long-term prognosis is uncertain

More general terms

• neuromuscular disease; myoneural disease

More specific terms

• Morfan's syndrome

Patient information

Isaac's syndrome patient information