Progressive myoclonic epilepsy

The progressive myoclonic epilepsies form a disparate group of rare severe conditions that are characterised by deteriorating action myoclonus, although other CNS symptoms and signs are often present.

• Unverricht–Lundborg disease (EPM1)

• Lafora body disease (EPM2)

• action myoclonus renal failure (AMRF) syndrome (EPM4)

• PRICKLE1-gene-related progressive myoclonic epilepsy with ataxia (EPM5)

• 'North Sea’ progressive myoclonus epilepsy (EPM6)

• myoclonic epilepsy with ragged-red fibres (MERRF)

• neuronal ceroid lipofuscinoses

• dentatorubral-pallidoluysian atrophy (DRPLA)

• sialidosis type 1 (cherry-red spot myoclonus syndrome)

• GM2 gangliosidoses

  • Tay–Sachs disease and variants

  • Sandhoff disease and variants

  • AB variant of GM2 gangliosidosis

• Gaucher disease: type 3 disease

Epidemiology

Most commonly they clinically manifest in late childhood or teens, although they may present at any age ¹.

Clinical presentation

The archetypal feature of the conditions is an action myoclonus, which demonstrates persistent worsening, but is also found at rest, and is precipitated by certain stimuli, including touch, loud sounds or light. 

Concurrent CNS features that are often - but not invariably - present, include:

• other forms of seizures: especially generalised tonic-clonic

• progressive ataxia

• dementia

Treatment and prognosis

The progressive myoclonic epilepsies are usually relatively refractory to antiseizure medications. Most patients eventually require wheelchairs with a decreased lifespan ¹.