Type 2 myotonic dystrophy

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Classification according to ICD-10
G71.1 Myotonic Syndrome
Proximal Myotonic Myopathy (PROMM)
ICD-10 online (WHO version 2019)

The myotonic dystrophy type 2 , shortly DM2 or PROMM even Proximal myotonic myopathy or Crohn Ricker called, is a form of myotonic muscular disease with muscle weakness, clouding of the lens and arrhythmia. With an incidence of 0.5 / 100,000 / year, it is less common than myotonic dystrophy type 1 . The inheritance is autosomal dominant .

clinic

Clinically, the PROMM manifests itself through a more proximally emphasized, myotonic myopathy, cardiac arrhythmias , lens opacities , testicular atrophy and pronounced therapy-resistant myalgias . The course is usually more benign than in myotonic dystrophy type 1 (Curschmann-Steinert's disease), and walking difficulties only appear in old age.

root cause

The cause is a genetic defect on chromosome 3q13.3-q24, with an expansion of CCTG repeats in the ZNF9 gene. The phenomenon of anticipation seems to be absent. The gene codes for the RNA-binding zinc finger protein 9 .

Diagnosis

Muscle biopsy in myotonic dystrophy type 2 with groups of highly atrophic type II fibers (highlighted) which remain unstained in the immunohistochemical staining for type 1 myosin ("slow myosin", here brown).

In addition to the clinical examination, the examination and diagnosis are usually initially carried out by measuring the electrical muscle activity in an electromyogram (EMG). In the electromyogram, myotonic salvos typically occur, which were formerly also characterized acoustically as a so-called dive bomber noise . Since myotonic salvos can also occur in other diseases, for example myotonic dystrophy type 1, the diagnosis is confirmed by means of direct genetic diagnostics from leukocytes .

If a muscle biopsy is performed, unspecific myopathic changes and typically groups of highly atrophic fibers, which are predominantly type II fibers, are found.

literature

Individual evidence

  1. ^ BG Schoser, C. Schneider-Gold, W. Kress, HH Goebel, P. Reilich, MC Koch, DE Pongratz, KV Toyka, H. Lochmüller, K. Ricker: Muscle pathology in 57 patients with myotonic dystrophy type 2. In : Muscle & nerve. Volume 29, Number 2, February 2004, pp. 275-281, ISSN  0148-639X . doi: 10.1002 / mus.10545 . PMID 14755494 .

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