Myotonic dystrophy

Myotonic dystrophy
Other names	Dystrophia myotonica,[1] myotonia atrophica,[1] myotonia dystrophica,[1] Curschmann–Batten–Steinert syndrome
Areas of body affected in myotonic dystrophy, types 1 and 2, colored in red
Specialty	Neurology, neuromuscular medicine, physical medicine and rehabilitation, medical genetics, pediatrics
Symptoms	Muscle loss, weakness, muscles which myotonia[1]
Complications	Cataracts, intellectual disability, heart conduction problems[1][2]
Usual onset	20s to 30s[1]
Duration	Long term[1]
Types	Type 1, type 2[1]
Causes	Genetic disorder (autosomal dominant)[1]
Diagnostic method	Genetic testing.[2]
Treatment	Braces, wheelchair, pacemakers, non invasive positive pressure ventilation[2]
Medication	Mexiletine, carbamazepine, tricyclic antidepressants, nonsteroidal anti inflammatory drugs[2]
Frequency	>1 in 8,000 people[1]

Myotonic dystrophy (DM) is a type of muscular dystrophy, a group of genetic disorders that cause progressive muscle loss and weakness.^[1] In DM, muscles are often unable to relax after contraction.^[1] Other manifestations may include cataracts, intellectual disability and heart conduction problems.^[1][2] In men, there may be early balding and infertility.^[1] While myotonic dystrophy can occur at any age, onset is typically in the 20s and 30s.^[1]

Myotonic dystrophy is caused by a genetic mutation in one of two genes. Mutation of the DMPK gene causes myotonic dystrophy type 1 (DM1). Mutation of CNBP gene causes type 2 (DM2).^[1] DM is typically inherited, following an autosomal dominant inheritance pattern,^[1] and it generally worsens with each generation.^[1] A type of DM1 may be apparent at birth.^[1] DM2 is generally milder.^[1] Diagnosis is confirmed by genetic testing.^[2]

There is no cure.^[3] Treatments may include braces or wheelchairs, pacemakers and non-invasive positive pressure ventilation.^[2] The medications mexiletine or carbamazepine can help relax muscles.^[2] Pain, if it occurs, may be treated with tricyclic antidepressants and nonsteroidal anti-inflammatory drugs (NSAIDs).^[2]

Myotonic dystrophy affects about 1 in 2,100 people,^[4] a number that was long estimated to be much lower (often cited as 1 in 8,000), reflecting that not all patients have immediate symptoms and, once they do have symptoms, the long time it typically takes to get to the right diagnosis.^[1] It is the most common form of muscular dystrophy that begins in adulthood.^[1] It was first described in 1909, with the underlying cause of type 1 determined in 1992.^[2]