From OMIM
Myotonic dystrophy (DM) is a multisystem disorder and the most common form of muscular dystrophy in adults. Individuals with DM2 have muscle pain and stiffness, progressive muscle weakness, myotonia, male hypogonadism, cardiac arrhythmias, diabetes, and early cataracts. Other features may include cognitive dysfunction, hypersomnia, tremor, and hearing loss (summary by Heatwole et al., 2011). See also myotonic dystrophy-1 (DM1; 160900), caused by an expanded CTG repeat in the dystrophia myotonica protein kinase gene (DMPK; 605377) on 19q13. Although originally reported as 2 disorders, myotonic dystrophy-2 and proximal myotonic myopathy are now referred to collectively as DM2 (Udd et al., 2003).  http://www.omim.org/entry/602668

From MedlinePlus Genetics
There are two variations of myotonic dystrophy type 1: the mild and congenital types. Mild myotonic dystrophy is apparent in mid to late adulthood. Affected individuals typically have mild myotonia and cataracts. Congenital myotonic dystrophy is often apparent at birth. Characteristic features include weak muscle tone (hypotonia), an inward- and upward-turning foot (clubfoot), breathing problems, delayed development, and intellectual disability. Some of these health problems can be life-threatening.

There are two major types of myotonic dystrophy: type 1 and type 2. Their signs and symptoms overlap, although type 2 tends to be milder than type 1. The muscle weakness associated with type 1 particularly affects muscles farthest from the center of the body (distal muscles), such as those of the lower legs, hands, neck, and face. Muscle weakness in type 2 primarily involves muscles close to the center of the body (proximal muscles), such as the those of the neck, shoulders, elbows, and hips. The two types of myotonic dystrophy are caused by mutations in different genes.

Other signs and symptoms of myotonic dystrophy include clouding of the lens of the eye (cataracts) and abnormalities of the electrical signals that control the heartbeat (cardiac conduction defects). Some affected individuals develop a condition called diabetes mellitus, in which blood sugar (glucose) levels can become dangerously high. The features of myotonic dystrophy often develop during a person's twenties or thirties, although they can occur at any age. The severity of the condition varies widely among affected people, even among members of the same family.

Myotonic dystrophy is characterized by progressive muscle wasting and weakness. People with this disorder often have prolonged muscle contractions (myotonia) and are not able to relax certain muscles after use. For example, a person may have difficulty releasing their grip on a doorknob or handle. Also, affected people may have slurred speech or temporary locking of their jaw.

Myotonic dystrophy is part of a group of inherited disorders called muscular dystrophies. It is the most common form of muscular dystrophy that begins in adulthood.  https://medlineplus.gov/genetics/condition/myotonic-dystrophy