Table 1.

Clinical manifestations of myotonic dystrophy type 2

Core features
Clinical myotonia	Present in fewer than half
Myotonia on electromyography	Absent or variable in many patients
Muscle weakness	Onset may occur after age 60–70 years
Cataracts	Present in a minority of patients
Localization of muscle weakness
Facial weakness, jaw muscles	Usually absent
Bulbar weakness, dysphagia	Absent
Respiratory muscles	Exceptional cases
Distal limb muscle weakness	Flexor digitorum profundus on testing, only in some patients
Proximal limb muscle weakness	The main disability in most patients
Sternocleidomastoid weakness	Prominent in few patients
Muscle symptoms
Myalgic pain	The most disabling symptom in many patients
Muscle strength variations	Can be considerable
Visible muscle atrophy	Usually absent
Calf hypertrophy	Present in half or more
Muscle biopsy findings
Fiber atrophy	Highly atrophic type 2 fibers
Nuclear clump fibers	Scattered early, before weakness is clinically evident
Cardiac arrhythmias	From absent to severe
Brain
Tremors	Prominent in many patients
Behavioral change	Not apparent
Hypersomnia	Infrequent
Cognitive decline	Not apparent
Other features
Anticipation	Exceptional
Childhood-onset central nervous system involvement	Absent
Congenital form	Absent