Cataracts can be either a cortical cataract with a blue dot appearance, or a posterior subcapsular cataract. Other organs affected include the heart, lungs, gastrointestinal tract, skin, and brain. Insulin resistance can also occur. Signs and symptoms vary considerably by severity, unusual phenotype, and form (DM1/DM2). DM1 and DM2 differ in regards to the muscles they affect, age of onset, severity of disease, and extramuscular manifestations. DM1
DM1 usually begins in the muscles of the hands, feet, neck, or face. One manifestation of facial weakness is drooping of the eyelid (ptosis). It slowly progresses to involve other muscle groups, including the heart. Myotonia tends to be more prominent in DM1 compared to DM2. Other DM1 manifestations include problems with executive function (e.g., organization, concentration, word-finding) and hypersomnia. Abnormalities in the electrical activity of the heart are common in DM1, manifesting as arrhythmias or conduction blocks. Sometimes, dilated cardiomyopathy occurs. Symptoms onset any time from birth to adulthood. The earlier the disease onset, the greater the variety of possible signs and symptoms. Thus, various diagnostic classifications based on the age of onset/severity of the disease have been proposed, although DM1 manifestations likely lie on a continuum. Congenital DM1
When DM1 onsets at birth, it is called congenital DM1. Manifestations that can be present at birth include hypotonia, respiratory failure, feeding difficulty, and club foot (talipes equinovarus), any of which tend to resolve over several years. During childhood, intellectual impairment, attention deficit hyperactivity disorder (ADHD), and autism spectrum disorders (ASD) can result.
Mutated DMPK RNA binds to MBNL1, causing ClC-1 pre-mRNA to be spliced into the fetal form instead of the adult form. Functional loss of the chloride channel causes myotonia. Histology
In DM1, there can be increased central nuclei, angular fibers, fiber atrophy, and pyknotic clumps. There can be selective atrophy of type 1 muscle fibers. Muscle fibers show signs of degeneration and regeneration. There is modest fibrosis of the endomysium.In DM2, there can be variation in the sizes of muscle fibers, although often there are no abnormalities. There is selective atrophy of type 2 muscle fibers. Again, there are central nuclei and nuclear clumps. Diagnosis
The diagnosis of DM1 and DM2 can be difficult due to the large number of neuromuscular disorders, most of which are very rare. One study found that diagnosis is made an average of seven years after symptom onset for DM1, and fourteen years for DM2.As a result, people with multiple symptoms that may be explained by a complex disorder such as DM1 or DM2 will generally be referred by their primary care physician to a neurologist for diagnosis. Depending on the presentation of symptoms, people may be referred to a number of medical specialists including cardiologists, ophthalmologists, endocrinologists, and rheumatologists. In addition, the clinical presentation is obscured by the degree of severity or the presence of unusual phenotypes. Though there is presently no cure for DM and management is currently symptom-based, a precise diagnosis is still necessary to anticipate multiple other problems that may develop over time (e.g. cataracts).