**4. Medical classification of ALS**

Making a proper diagnosis in ALS is complicated because symptoms can vary in each patient. Based on the symptom, ALS can be classified in five broad ranges based on the disease symbol:

Classical ALS – characterized by the deterioration of upper and lower motor neurons [nerve cells]. This symptom generally affects more than two-thirds of patients with the disease.

Primary lateral sclerosis [PLS] – in which case the upper motor neurons deteriorate. If the lower motor neurons are not affected within 2 years, the disease usually remains a pure upper motor neuron disease. It is the rarest form of ALS.

Progressive bulbar palsy [PBP] – this condition starts with difficulties in speaking, chewing and swallowing due to lower motor neuron [nerve cell] deterioration. It affects about 25% of those with ALS.

Progressive muscular atrophy [PMA] – in which the lower motor neurons deteriorate. If the upper motor neurons are unaffected within 2 years of contracting the disease, the disease usually remains a pure lower motor neuron disease.

Familial – that affects more than one member of the same family (adapted from http:// www.hopkinsmedicine.org/neurology\_neurosurgery/centers\_clinics/als/conditions/ als\_amyotrophic\_lateral\_sclerosis.html).
