Muscular dystrophy (MD) refers to a group of nine genetic diseases that cause progressive weakness and degeneration of muscles used during voluntary movement; myotonic dystrophy is the most common form seen in adults
Aetiology
Autosomal dominant - two different triple repeat mutations
Patients usually present in their 20s
Clinical features
Myotonia - continued, involuntary muscle contraction after cessation of voluntary effort (failure of relaxation)
Features in the face: frontal balding, myopathic facies (a long and thin face), bilateral ptosis, cataracts
Features in speech: dysarthria (caused by a myotonic tongue and pharyngeal muscles)
Features in the neck: wasted sternocleidomastoid muscles
Features in the hands: distal wasting and weakness, slow relaxing grip, percussion myotonia (thumb flexion on percussion of the thenar eminence)