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Incidence (average around 1/50,000 per year) and prevalence (average around 1/20,000) are relatively uniform in Western countries, although foci of higher frequency have been reported in the Western Pacific. The mean age of onset for sporadic ALS is about 60 years. Overall, there is a slight male preponderance (male to female ratio of around 1.5:1).

Approximately two thirds of patients with typical ALS have a spinal form of the disease (limb onset) and present with symptoms related to focal muscle weakness and wasting, in which onset of symptoms may start either distally or proximally in the upper and lower limbs. Gradually, spasticity may develop in the weakened atrophic limbs, affecting manual dexterity and gait. Patients with bulbar onset ALS usually present with dysarthria and dysphagia for solids or liquids. Limb symptoms can develop almost simultaneously with bulbar symptoms, and in the vast majority of cases will occur within 1-2 years. Paralysis is progressive and leads to death due to respiratory failure within 2-3 years for bulbar onset cases and 3-5 years for limb onset ALS cases.

Most ALS cases are sporadic but 5-10% of cases are familial, and of these 20% involve a mutation of the SOD1 gene (21q22.11), about 2-5% involve mutations of the TARDBP gene (1p36.22) encoding the TAR DNA-binding protein 43 (TDP-43) and 1-2% involve mutations of the VCP gene (9p13.3) coding for the Valosin Containing Protein. Two percent of apparently sporadic cases involve SOD1 mutations, and TARDBP mutations have also been identified in sporadic cases.

The diagnosis is based on clinical history, examination, electromyography, and exclusion of 'ALS-mimics' (e.g. multifocal motor neuropathy, Kennedy's disease (seethese terms) and cervical spondylotic myelopathy) by appropriate investigations. The pathological hallmarks comprise loss of motor neurons with intraneuronal ubiquitin-immunoreactive inclusions in upper motor neurons and TDP-43 immunoreactive inclusions in degenerating lower motor neurons. Signs of upper motor neuron and lower motor neuron damage not explained by any other disease process are suggestive of ALS.

The management of ALS is supportive, palliative, and multidisciplinary. Non-invasive ventilation prolongs survival and improves quality of life. Riluzole is the only drug that has been shown to extend survival.