Clinical features

The cardinal feature of myotonic dystrophy is myotonia although this often lessens and may disappear as the disease progresses.

In the face:

• frontal baldness
• myopathic face with ptosis, hanging jaw, wasting of muscles of mastication, hollowing of temporal fossae and cheeks - sometimes described as a fish face
• wasting of sternocleidomastoid - weak neck flexion, normal neck extension, swan neck appearance
• cataracts in 80% of cases

In the limbs:

• characteristic is the inability of the patient to let go of the examiner's hand when they shake hands
• percussion myotonia - via tapping over the thenar eminence - may result in contraction and slow relaxation of opponens pollicis
• wasting and weakness distally

Others features include:

• testicular atrophy in males
• mental impairment in 30% of cases

Note that non-neurological manifestations - frontal baldness, cataracts especially in the posterior part of lens, infertility - may predate muscle weakness and myotonia.