Uncovering amyotrophic lateral sclerosis phenotypes: clinical features and long-term follow-up of upper motor neuron-dominant ALS.

The aim of our study was to analyse the natural history and clinical features of upper motor neuron- dominant (UMN-D) ALS. We studied a large series of sporadic ALS patients admitted in a single referral centre over a 23-year period. UMN-D phenotype was compared with other ALS forms, including classic ALS, flail arm and progressive muscular atrophy. Seven hundred and thirty-four sporadic ALS patients were included of which 163 had UMN-D ALS. The mean age of onset in UMN-D ALS (52 years) was 10 years lower than in classic ALS (61.4 years, p < 0.0001); sex ratio by age groups significantly differed with respect to other phenotypes. The pattern of spread of lower motor neuron signs in UMN-D was characterized by early involvement of upper limb muscles and late impairment of respiratory muscles. Duration of the disease was longer in the UMN-D group (56 months) than in classic ALS (33 months, p < 0.001). The UMN-D phenotype was a strong independent predictor of long survival. In summary, UMN-D ALS showed significant differences in age of onset, sex ratio, pattern of spreading and prognosis with respect to other ALS forms, most probably reflecting biological differences.