Clinical features: 1. slow progression with insidious onset after 30 years of age; autosomal dominant inheritance with family history; 2. wide variation in severity among patients; some patients can be detected only during physical examination. 3, muscle ankylosis: the muscle cannot be released normally after contraction; it mainly affects hand, head and facial movements, walking and eating; muscle ball formation can be seen when the muscle is clasped. Symptoms are aggravated by cold; improve after activity; 4, muscle weakness and atrophy: temporal and biting muscles are the most obvious, resulting in a long, thin face with elevated cheekbones and a “goose neck”; 5, extra skeletal muscle manifestations: cataracts, endocrine disorders (testicular microcephaly). Endocrine disorders (small testes, irregular menstruation, premature menopause, infertility, abnormal glucose tolerance or diabetes, broad forehead, baldness), myocardial involvement (arrhythmia, palpitations, syncope, atrioventricular block of degree II-III), gastrointestinal smooth muscle involvement (pseudo-intestinal obstruction, constipation, anal sphincter involvement leading to fecal incontinence), mental retardation, ventricular enlargement, hearing impairment, excessive sweating, etc.; electromyography: important diagnostic basis; myotonic discharge + myogenic damage; genetic testing 1. DM1 – dynamic mutation of myotonic protein kinase gene ctg at locus 13.3 of the long arm of chromosome 19 (patient:50-2000 to 4000, normal: 5 to 40); common; 2. DM2 – abnormal nucleotide repeat sequence CCTG within the intron of the zinc finger protein gene of chromosome 3q21.3 Amplification up to 75 ~ 11000 times; DM2 disease age later than the adult onset of DMl, the average age of onset of 48 years, there is no report of congenital onset; early manifestations of proximal muscle involvement, force weakness characteristic distribution is the flexor and extensor muscles (often the first point of force weakness), cervical flexors, elbow extensors and finger flexors. Pain is a prominent feature of DM2; DM2 endocrine changes are more common than DMl but no gastrointestinal symptoms; 3, DM3 – non-CTG non-CCGT repeat extended DM. Blood ck: normal or only mildly elevated; Differential diagnosis 1, congenital myotonia (myotonia congenita, Thomson’s disease): also autosomal dominant (1) infant or (2) muscle hypertrophy resembling that of an athlete, without myasthenia; (3) no endocrine or cardiac involvement; (4) some patients have psychiatric symptoms: irritability, depression, obsessive-compulsive ideas; (5) no myogenic damage on EMG; (2) congenital paramyotonia congenita: also autosomal dominant (1) onset after birth; (2) paramyotonia congenita: also autosomal dominant (2) paradoxical myotonia: appears after activity; (3) mostly involves the muscles of the face and distal upper limbs; myotonia appears after exposure to cold and disappears rapidly in the warm state; (3) neuromyotonia (Isaacs’ syndrome): (1) onset in childhood or adolescence; (2) persistent muscle tremors (if you touch the muscles during the tremors with your hands, you will feel a pile of writhing snakes through the sack), with sweating (3) muscle twitching on EMG; treatment: no cure; symptomatic: mainly for myotonic symptoms – quinine or procainamide (contraindicated in heart block), carbamazepine, phenytoin sodium and other sodium channel blocking drugs; confirmed by foreign clinical studies Slow heart rhythm (Mexiletine, Mexiletine) and Tocainide are superior to phenytoin, but Mexiletine is more effective for sodium channel myotonicity such as potassium deterioration myotonicity, congenital paramyotonicity, and hyperkalemic periodic paralysis as opposed to chloride channel myotonicity such as ankylosing myotonic dystrophy and congenital myotonicity.