Myotonic Dystrophy type 2 also called Proximal Myotonic Myopathy (PROMM) is a rare genetic multi-system disorder of late childhood or adult-onset characterized by mild myotonia, muscle weakness, and rarely cardiac conduction disorders. It is an autosomal, dominant disorder caused by the expansion of a (CCTG)n quadruplet repeat in CNBP gene located on chromosome 3. His prevalence is low (1/100000?) and seems higher in countries like Germany and U.S.
DM2 typically appears in adult life and has variable manifestations, such as early-onset cataracts (younger than 50 years), varying grip myotonia, thigh muscle stiffness, and muscle pain, as well as weakness. There is no congenital form.
Symptoms usually begin in the second to sixth decade (median age 48 years). Early in the presentation of DM2 there is only mild weakness of hip extension, thigh flexion, and finger flexion.
Extensive pain is frequently reported in DM2 and includes abdominal, musculoskeletal, and exercise-related pain. The pain tends to come and go without obvious cause and usually fluctuates in intensity and distribution over the limbs. It may share similar features with fibromyalgia and a prior diagnosis of fibromyalgia is relatively common.
Cardiac problems appear to be less severe and frequent in patients with DM2 than in patients with DM1. Clinically significant cardiac features in DM2 include arrhythmias, atrioventricular conduction defects, and even overt dilated cardiomyopathy. A high prevalence of atrial fibrillation and left ventricular dysfunction have been reported in DM2 patients.
Contrary to DM1, no ventilatory insufficiency has been reported in DM2.
The type of cognitive impairment that occurs in DM2 is similar to but less severe than that of DM1. Cognitive abnormalities and a reduction in cerebral blood flow in the frontal and temporal poles occur and occasionally there are alterations in the white matter of the brain.
Other manifestations, such as hypogonadism, glucose intolerance, excessive sweating and dysphagia may also occur and worsen over time.
Research is less advanced for DM2 than DM1. Registries developed for DM1 usually include DM2.
There is currently no treatment available to stop or slow the progression of myotonic dystrophy type 2. Management options depend on the symptoms that each affected person has, and aim to treat each specific symptom.
DM2 is diagnosed through a physical exam. Electromyography and blood tests are also used to clarify the clinical diagnosis. Nevertheless, the usual weakness of visible signs may result in misdiagnosis.