muscular dystrophy vs myotonic muscular dystrophy

As nouns, myotonic muscular dystrophy is a hyponym of muscular dystrophy; that is, myotonic muscular dystrophy is a word with a more specific, narrower meaning than muscular dystrophy:

• muscular dystrophy: any of several hereditary diseases of the muscular system characterized by weakness and wasting of skeletal muscles
• myotonic muscular dystrophy: a severe form of muscular dystrophy marked by generalized weakness and muscular wasting that affects the face and feet and hands and neck; difficult speech and difficulty with the hands that spreads to the arms and shoulders and legs and hips; the onset can be any time from birth to middle age and the progression is slow; inheritance is autosomal dominant