Benign Congenital Hypotonia

Synonym: Congenital hypotonia with favourable outcome (CHFO).

The diagnosis of Benign Congenital Hypotonia (BCH) is now a controversial one.¹ Since the first description in 1956 it has been possible more accurately to diagnose children who would otherwise have received this diagnosis.^2,3

However, the term benign congenital hypotonia is still used to describe children with mild hypotonia who appear to have a favourable outcome and in whom no other diagnosis can at this stage be made.

The criteria initially suggested for the diagnosis are:⁴

• Early hypotonia - usually since birth.
• Active movements of the limbs and normal tendon reflexes.
• Normal or mild motor retardation that improves with age.
• Normal levels of muscle enzymes.
• Normal results of electromyelography and nerve conduction studies.⁵
• Normal muscle biopsy studies.

• The true incidence of benign congenital hypotonia is not known but is less than first thought as many have now received other diagnoses.
• There is a familial tendency with approximately 30% of affected children having some family history.⁶
• Boys and girls appear to be equally affected.

The children present at birth as "floppy babies" with generalised hypotonia. They may also have any combination of the following features:

• Accentuation of the spinal curve, e.g. hyperlordosis
• Abdominal protrusion
• "Flat feet" when standing
• Pes cavus - when not weight bearing
• Walking on "tip-toe"
• Inability to walk on heels (common)
• Developmental delay, i.e. failing to meet gross motor milestones for sitting, standing and walking
• ± Muscle contractures (not before age of 8 years)
• Joint hyperlaxity
• Recurrent episodes of myalgia when using muscles

The diagnosis of BCH must be made when other causes of hypotonia have been ruled out. Other diagnoses which must be considered include:

• Congenital myotonic dystrophy
• Nemaline myopathy; congenital myopathy characterised by abnormal rod-like structures in muscle fibres on histological examination⁷
• Metabolic disorders e.g. Zellweger syndrome
• Prader-Willi syndrome
• Werdnig-Hoffman disease
• Down's syndrome
• Infantile botulism

A full history should be taken from the parents of any child with hypotonia looking for evidence of:

• Birth trauma
• Family history of hypotonia
• Perinatal asphyxia
• Infection and/or drugs taken by mother during pregnancy

Examination should be undertaken to ascertain the pattern of weakness and also to look for any other congenital abnormalities.
Other investigations may include:

• Infection screen - including CSF and blood culture
• Blood tests, e.g. for glucose, magnesium, creatine kinase
• Karyotyping
• CT/MRI scan
• Muscle biopsy
• Electromyelography (EMG):
  • Normal EMG examination helps investigators to exclude several neurological diseases characterized by hypotonia.
  • It can provide valuable information to confirm the clinical diagnosis of BCH.⁵
• Nerve conduction studies

General measures

Although no drug therapy is currently available for the treatment of BCH, children benefit from treatment with physiotherapy to help both active and passive movements in order to optimise muscle strength and prevent the development of any shortening of the muscles.⁴

Parents will benefit from reassurance that the disorder is usually self-limiting, is not associated with any intellectual deficit and disappears by puberty in the majority of cases.