Snapshot A 35-year-old man presents to his primary care physician's office for difficulty chewing and walking and mild musclar pain. He notices himself dragging his feet while walking and pain in his legs. He experiences stiffness in his jaw and his hands. On physical exam, there is bilateral ptosis and atrophy of the temporalis muscle. There is weakness with turning of the neck and bilateral dorsiflexion. A serum creatine kinase is normal. Genetic testing shows CTG nucleotide expansion on the DMPK gene on chromosome 19. Introduction Clinical definition a hereditary disorder that results in a number of clinical consequences such as sustained muscle contraction (myotonia) muscle weakness cataracts frontal balding arrhythmias Epidemiology incidence most common type of muscular dystrophy in adults especially with European ancestry risk factors family history Etiology genetics myotonic dystrophy (MD) type 1 autosomal dominant mutation in DMPK gene on chromosome 19 leads to a CTG trinucleotide expansion Pathogenesis unclear, but it is believed that the abnormal mRNA transcript of DMPK impairs RNA splicing, which leads to missplicing of other RNA transcripts Prognosis 30-50% of cases leads to disability in adulthood most common causes of death are respiratory diseases (e.g., respiratory failure) cardiac diseases (e.g., arrhythmia) Presentation Symptoms muscle stiffness muscle weakness and pain visual problems excessive daytime sleepiness Physical exam muscle weakness that is typically found in the face or jaw commonly as ptosis distal limb muscles sternocleidomastoid muscle muscle atrophy that is typically found in the face temporal distal hands legs myotonia cataracts frontal balding testicular atrophy Studies Labs serum creatine kinase normal-to-moderate increase Genetic testing gold standard Slit-lamp examination to evaluate for cataracts classically posterior subcapsular cataracts Electrocardiogram critical in the evaluation of cardiac conduction defects Making the diagnosis based on clinical presentation and confirmed with genetic testing Differential Limb-girdle muscular dystrophy Spinal muscular atrophy Treatment Management approach there are no disease modifying treatments and thus management involves a multidisciplinary approach for example cardiac pacemakers in patients with life-threatening cardiac arrhythmias surgery for cataract extraction non-invasive positive pressure ventilation in patients with obstructive sleep apnea Complications Cardiovascular disease and arrhthmias Hyperinsulinemia Pregnancy complications such as spontaneous abortion preterm labor Obstructive sleep apnea Hypothyroidism Increased cancer susceptibility Cataracts