Definition

Infantile spasms is an epileptic syndrome characterised by the triad of myoclonic spasms, hypsarrhythmia and arrest of psychomotor development at onset.

History

Infantile spasms were first described by West (1841). His paper, published in the first volume of Lancet was a landmark in the development of paediatric neurology. West observed the condition in his own child, giving a precise and complete description of the symptoms, and the gradual mental deterioration, recognising the intractability of the syndrome.

For many years, infantile spasms was considered a rare condition, and only 68 cases had been reported in the literature before 1940.

With the development of the EEG, the characteristic signature of hypsarrhythmia was identified by Gibbs and Gibbs (1952).

Incidence

Widely varying rates of incidence have been reported; these are caused by three factors:

• Variation in incidence of epilepsy in different populations by a factor of as much as 10
• Interpretation of the definition of the syndrome
• Changing incidence with time

The best estimate of incidence appears to be between 1 in 2,000 and 1 in 4,000 live births (Hurst, 1994); this represents 25 - 30% of childhood epilepsies.

It is likely that the incidence of infantile spasms is increasing due to reduced mortality before and immediately after birth.

The age of onset is from 3 to 12 months, peaking at 4 to 7 months. More prevalent in boys than girls. The clinical definition of infantile spasms excludes cases developing after 12 months, although it does appear that a small risk of infantile spasms developing up to the age of 11 years.

Prior risk factors are hereditary epilepsy, tuberous sclerosis, brain malformation, genetic metabolic disorders, cerebral hypoxic events (ie starvation of oxygen to brain), usually at birth, and head trauma.

Clinical features

Fits occur as a cluster of myoclonic spasms (typically 5 to 10). About 30% are flexor (contraction of head or limbs), 20% are extension (arching) and 50% are mixed.

Investigations

Mainly recognised by characteristic fit pattern. EEG shows hypsarrhythmia in 60%+ of cases at onset. CT and MRI abnormalities in 70%+ of cases (focal atrophy 35%, generalised atrophy 20%).

Treatment

The first line of treatment is ACTH, typically 20-40 units a day. ACTH treatment is usually only for a short period, because of the many serious side effects. Surprisingly, there have been no controlled studies to demonstrate the effectiveness of ACTH. Prednisolone, another steroid is also used as a short term treatment

Infantile spasms is refractive to drug treatment. Currently the treatment of choice is vigabatrin (sabril). Other drugs used include clonazepam, clobazam, nitrazepam and valproic acid. Drug treatment is only successful in about 35% of cases.

The ketogenic diet is potentially an important treatment for infantile spasms. Often used as a treatment of last resort, it fully controls infantile spasms in 25% to 50% of cases, and partially controls infantile spasms in 25% of cases (there are no satisfactory clinical trials to support these figures). Infantile spasms seems particularly suitable for the ketogenic diet, because the frequency of fits makes it possible to monitor and fine tune the diet with precision.

Prognosis

The spasms usually remit spontaneously after a few months, often to be replaced by other forms of epilepsy before the age of 5; only 15% of cases have complete recovery. 30% of cases progress to Lennox-Gastaut syndrome. 60% of cases have metal retardation at onset, rising to 80% subsequently.

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