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 1956,² it has been possible to more accurately diagnose children who would otherwise have received this diagnosis.³ The term benign congenital hypotonia is still however 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 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
• ± Muscle contractures (not before age of 8)
• 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 such as 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- CSF, blood
• Blood tests for e.g. glucose, magnesium, creatine kinase
• Karyotyping
• CT/MRI scan
• Muscle biopsy
• Electromyelography; a normal EMG examination helps investigators to exclude several neurological diseases characterized by hypotonia and it can provide valuable information to confirm the clinical diagnosis of BCH.⁵
• Nerve conduction studies

Non-drug

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