General description

Myotonic dystrophy (DM) is the most common form of muscular dystrophy in adults, characterized by progressive muscle weakness, myotonia (difficulty relaxing muscles after contraction), and multi-organ involvement. The disorder follows an autosomal dominant inheritance pattern and often exhibits anticipation, where symptoms worsen with each generation. Onset typically occurs in the 20s or 30s, but congenital forms of DM1 can manifest at birth, presenting with severe muscle weakness. The average life expectancy is around 55 years and has not significantly improved in recent decades.

DM is classified into two subtypes:

• DM1: Caused by an abnormal expansion of CTG repeats in the DMPK (myotonic dystrophy protein kinase) gene on chromosome 19. Normal individuals have fewer than 35 repeats, while those with DM1 have 50 or more, with congenital cases often exhibiting thousands of repeats.
• DM2: Much rarer and typically milder, caused by mutations in the CNBP gene.

The expanded repeat in DM1 leads to abnormal mRNA splicing, resulting in diverse symptoms including:

• Muscular symptoms: Weakness and atrophy, especially in distal limbs, temporalis, and sternocleidomastoid muscles. A characteristic "hatchet face" appearance and myotonia (e.g., difficulty releasing a handshake) are often observed.
• Cardiac involvement: Conduction defects and cardiomyopathy.
• Central nervous system: Cognitive impairment, personality changes, and excessive daytime sleepiness.
• Ocular symptoms: Early-onset cataracts and retinal degeneration.
• Endocrine issues: Insulin resistance, hyperlipidemia, and infertility in men (often associated with early balding).

Diagnosis is confirmed through genetic testing. Symptoms like white matter cataracts, distal muscle weakness, and frontal balding are important diagnostic clues. While DM2 shares some features with DM1, it is generally milder, with later onset and less severe systemic involvement.

General description

MRI reveals generalized cerebral atrophy and enlargement of the lateral ventricles. T2WI and FLAIR show bilateral white matter hyperintensity, which correlates with the progression of dementia. Characteristic white matter signal abnormalities are particularly evident in the white matter of the temporal poles and insula.