Neuromuscular Disorders in Children by Unknown

Author:Unknown
Language: eng
Format: epub
Tags: N/A
Publisher: Mac Keith Press
Published: 2019-07-08T00:00:00+00:00

14

CONGENITAL MYOPATHIES

Sandra Coppens

Introduction

The congenital myopathies (CM) are a broad group of genetic muscle disorders characterized by hypotonia and muscle weakness with a neonatal or early onset and a stable or slowly progressive course. The prevalence of congenital myopathies was estimated at 1 in 26 000 in the United States (Amburgey et al. 2011) and at 1 in 20 000 in Sweden (Darin and Tulinius 2000).

Classification

Classically, congenital myopathies are classified into four main subtypes based on the main histological findings from muscle biopsies (Fig. 14.1):

• nemaline myopathies (NM);

• core myopathies (central core disease [CCD] or multiminicore disease [MmD]);

• congenital fibre type disproportion (CFTD);

• centronuclear myopathies (CNM).

It is important to note that many patients with congenital myopathies cannot be classified into one of these four main histological subtypes due to the presence of non-specific changes in the muscle biopsy or to the presence of features overlapping several histological subtypes. Muscle biopsy alone is often not sufficient for an efficient aetiologic diagnosis of the congenital myopathies (North et al. 2014). Combining clinical assessment, muscle histology, muscle magnetic resonance imaging (MRI) and modern genetic tools now allows a rapid and efficient aetiologic diagnosis in more than 50% of patients with a congenital myopathy.

Clinical features

The first signs of the congenital myopathies can be present during the prenatal period with decreased fetal movements, polyhydramnios and joint contractures (club feet, arthrogryposis). Prematurity is more frequent in patients with congenital myopathies (especially with MTM1-related myopathy). At birth, patients are usually hypotonic (floppy infant) and weak, in contrast to babies with central nervous system lesions that are hypotonic but have a normal limb strength. Some congenital myopathies patients have a myopathic facies (long and narrow facies with open mouth), ophthalmoplegia and signs of bulbar weakness (difficulty with sucking and swallowing, weak cry, high-arched palate). At examination, patients display an abnormal traction response with head lag. On vertical suspension, they slip through the examiner’s hands because of the weakness of the shoulder girdle. Lower limbs are extended and externally rotated (frog-legged lower limb posture) with few or absent spontaneous movements. Reflexes are depressed or absent. Contractures are usually milder than in congenital muscular dystrophies or COL6-related myopathies but Achilles tendon contractures are frequent. Intellect is usually normal (North et al. 2014).

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