Prevalence estimates on Rare Medical Network websites are calculated based on data available from numerous sources, including US and European government statistics, the NIH, Orphanet, and published epidemiologic studies. Rare disease population data is recognized to be highly variable, and based on a wide variety of source data and methodologies, so the prevalence data on this site should be assumed to be estimated and cannot be considered to be absolutely correct.
Age of Onset
Autosomal dominant ?A pathogenic variant in only one gene copy in each cell is sufficient to cause an autosomal dominant disease
Autosomal recessive ?Pathogenic variants in both copies of each gene of the chromosome are needed to cause an autosomal recessive disease and observe the mutant phenotype
X-linked dominant ?X-linked dominant inheritance, sometimes referred to as X-linked dominance, is a mode of genetic inheritance by which a dominant gene is carried on the X chromosome.
X-linked recessive ?Pathogenic variants in both copies of a gene on the X chromosome cause an X-linked recessive disorder
Mitochondrial or multigenic ?Mitochondrial genetic disorders can be caused by changes (mutations) in either the mitochondrial DNA or nuclear DNA that lead to dysfunction of the mitochondria and inadequate production of energy.
Multigenic or multifactor ?Inheritance involving many factors, of which at least one is genetic but none is of overwhelming importance, as in the causation of a disease by multiple genetic and environmental factors.
Other Names (AKA)
Neuromyotonia; Isaac's-Merten's syndrome; Continuous muscle fiber activity syndrome;
Nervous System Diseases
- Progressive stiffness, cramping and weakness
- Muscle twitching with a rippling appearance (myokymia)
- Delayed muscle relaxation
- Diminished reflexes
- Muscle atrophy
Ataxia(difficulty coordinating voluntary movements)
- Increased sweating
These symptoms generally persist throughout the day, even during sleep or when under general anesthesia. Speech and breathing may also be affected if the muscles of the throat are involved. Smooth muscles and cardiac (heart) muscles typically are spared.
This table lists symptoms that people with this disease may have. For most diseases, symptoms will vary from person to person. People with the same disease may not have all the symptoms listed. This information comes from a database called the Human Phenotype Ontology (HPO) . The HPO collects information on symptoms that have been described in medical resources. The HPO is updated regularly. Use the HPO ID to access more in-depth information about a symptom.
|Medical Terms||Other Names||
|30%-79% of people have these symptoms|
|Calf muscle hypertrophy||
Increased size of calf muscles
|EMG: myokymic discharges||0100288|
[ more ]
|5%-29% of people have these symptoms|
|Distal sensory impairment||
Decreased sensation in extremities
|1%-4% of people have these symptoms|
Related diseases are conditions that have similar signs and symptoms. A health care provider may consider these conditions in the table below when making a diagnosis. Please note that the table may not include all the possible conditions related to this disease.
Conditions with similar signs and symptoms from Orphanet
Differential diagnosis includes hereditary neuromyotonia or myokymia (with/without episodic ataxia) syndromes, cramp-fasciculation syndrome, motor neuron diseases (progressive spinal muscle atrophy, neuropathy, amyotrophic lateral sclerosis (ALS) (see this term), intoxication (gold, mercury, toluene, insecticides) and tetanus (see this term).
Visit the Orphanet disease page for more information.
These resources provide more information about this condition or associated symptoms. The in-depth resources contain medical and scientific language that may be hard to understand. You may want to review these resources with a medical professional.
- The Merck Manual provides information on this condition for patients and caregivers.
- The National Institute of Neurological Disorders and Stroke (NINDS) collects and disseminates research information related to neurological disorders. Click on the link to view information on this topic.
- The National Organization for Rare Disorders (NORD) has a report for patients and families about this condition. NORD is a patient advocacy organization for individuals with rare diseases and the organizations that serve them.
- Medscape Reference provides information on this topic. You may need to register to view the medical textbook, but registration is free.
- The Merck Manual for health care professionals provides information on Isaacs' syndrome.
- The Monarch Initiative brings together data about this condition from humans and other species to help physicians and biomedical researchers. Monarch’s tools are designed to make it easier to compare the signs and symptoms (phenotypes) of different diseases and discover common features. This initiative is a collaboration between several academic institutions across the world and is funded by the National Institutes of Health. Visit the website to explore the biology of this condition.
- Orphanet is a European reference portal for information on rare diseases and orphan drugs. Access to this database is free of charge.
- PubMed is a searchable database of medical literature and lists journal articles that discuss Isaacs' syndrome. Click on the link to view a sample search on this topic.
- NINDS Isaac's Syndrome Information Page. National Institute of Neurological Disorders and Stroke (NINDS). September 2015; https://www.ninds.nih.gov/Disorders/All-Disorders/Isaacs-syndrome-Information-Page.
- Suying Song. Myokymia. Medscape Reference. November 2014; https://emedicine.medscape.com/article/1141267-overview.
- Ahmed A, Simmons Z. Isaacs syndrome: A review. Muscle Nerve. July 2015; 52(1):5-12.
- Acquired Neuromyotonia. NORD. 2014; https://rarediseases.org/rare-diseases/acquired-neuromyotonia/.