PEDBASE.org - The Pediatric Database - Detailed information of CONGENITAL MUSCLE FIBRE-TYPE DISPROPORTION

CONGENITAL MUSCLE FIBRE-TYPE DISPROPORTION

DEFINITION:

A congenital myopathy characterized by generalized hypotonia, muscle weakness, with small and numerous type 1 fibres on muscle biopsy.

EPIDEMIOLOGY:

incidence: rare
age of onset:
- newborn
risk factors:
- familial - autosomal recessive
  - chrom.#: ?
  - gene: ?
  - may also be sporadic and autosomal dominant forms
- M = F
- may be associated with:
  - cerebellar hypoplasia
  - Fetal Alcohol Syndrome
  - Krabbe's Disease
  - Myotonic Muscular Dystrophy
  - Nemaline Rod Myopathy
  - Rigid Spine Syndrome

PATHOGENESIS:

1. Genetic Defect

genetic defect -> ? neurogenic etiology -> abnormal neurological influence affects normal development of the motor unit -> maturational arrest of fetal muscle at myotubular stage (20-28 weeks gestational age) so that muscle biopsy has the appearance of an embryonic distribution of fibre type differentiation and growth

PATHOLOGY:

1. Muscle Biopsy

1. Type 1 Fibres

predominant and uniformly small in size
normal mature staining pattern

2. Type 2 Fibres

normal or large in size
normal mature staining pattern

CLINICAL FEATURES:

1. Neurological Manifestations

generalized mild infantile hypotonia and diffuse muscle weakness
- proximal > distal muscle groups
  - tends to be benign and nonprogressive
  - gross motor developmental delay
  - thin, wasted body habitus with decreased muscle bulk
- respiratory distress and dysphagia rare
- facial muscles -> myopathic facies
- ocular muscles -> ophthalmoplegia
- sternocleidomastoid muscle -> poor head control
deep tendon reflexes absent or depressed
normal intelligence

2. Musculoskeletal Manifestations

1. Dysmorphic Features

dolichocephalic head, high-arched palate

2. Skeletal

foot deformities
hip subluxation
kyphoscoliosis
mild congenital contractures of multiple joints
short stature

INVESTIGATIONS:

1. Serum

normal or slightly elevated CPK

2. EMG

normal

3. Nerve Conduction Studies

normal; ? denervation pattern

MANAGEMENT:

1. Supportive

multidisciplinary approach
- Paediatrics - promote ambulation and physiotherapy, moniter deformities
- Surgery - moniter and correct deformities
- Genetics - genetic counselling, ? prenatal diagnosis

Pediatric Database - CONGENITAL MUSCLE FIBRE-TYPE DISPROPORTION

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