Proximal Myotonic Myopathy (PROMM; DM2)

Proximal myotonic myopathy, also referred to as myotonic muscular dystrophy 2 (DM2), is a disorder with clinical similarities to DM1 (80). The abnormal protein in this autosomal-dominant disorder is the zinc finger protein 9 (ZNF9) with genetic loci at chromosome 3q21.

Clinical severity is unrelated to variablesize CCTG repeats. The prognosis is more benign than DM1, and there is not a severe congenital onset form. Onset is 8 to 60 years, and there is intrafamilial variability. Patients present with muscle stiffness and pain. Weakness involves the proximal legs (hip flexors and extensors) greater than the proximal legs as well as thumb and finger flexors. Facial weakness is seen in a minority of patients. Distal legs and respiratory muscles are not clinically affected. A hallmark is the enlargement of calf muscles. Muscle pain may be exercise-related, or at rest and increases with cold. The myotonia is severe, asymmetric, and intermittent from day to day. The myotonia actually inceases with warmth and decreases with cold. There is both grip and percussion myotonia. Cataracts are noted in all patients over 20 years with slit lamp examinations. Cardiac conduction defects are present in 20%, diabetes mellitus in 20%, and hearing loss in 20%. MRI shows white matter hyperintensity on T2-weighted images. CK is normal to less than 10 times elevated. EMG shows profound myotonia and compound muscle action potential (CMAP) amplitudes increment by 60% with exercise and reduce by 40% with rest. There is no decrement on short exercise or slow or rapid repetitive stimulation. Myopathic motor units are seen proximally. MRI shows selective muscle involvement of the erector spinae and gluteus maximus. Diagnosis is confirmed by molecular genetic studies.

<< | >>

↑

Source: Alexander M.A., Matthews D.J.. Pediatric Rehabilitation: Principles and Practice. 4 th. еd. — New York: Demos Medical Publishing,2010. — 540 р.. 2010

More medical literature on Medic.Studio

Proximal Myotonic Myopathy (PROMM; DM2)

More on the topic Proximal Myotonic Myopathy (PROMM; DM2):