Atypical forms of amyotrophic lateral sclerosis

This article provides a comprehensive overview of contemporary concepts regarding the classical and atypical phenotypes of amyotrophic lateral sclerosis (ALS), with a particular focus on critical diagnostic challenges. The classical variant of the disease is characterized by the progressive involvement of both upper and lower motor neurons, typically presenting with an asymmetric onset and a predictable progression. However, several atypical phenotypes are identified, including syndromes predominantly affecting the lower motor neurons, such as the «hanging hands» and «hanging legs» syndromes, isolated bulbar paralysis, ALS with respiratory onset, and forms with a predominance of upper motor neuron involvement. These atypical variants often mimic other neurological conditions-such as cervical myelopathy, multifocal motor neuropathy, and myasthenia gravis-which can result in significant delays in the accurate diagnosis of ALS. Atypical forms of ALS represent a major source of diagnostic errors in clinical practice. Enhancing healthcare professionals' understanding of the spectrum of phenotypic presentations, alongside the application of contemporary diagnostic criteria, facilitates more timely diagnoses, optimized patient care pathways, and the prompt initiation of pathogenetic therapies, ultimately improving both survival rates and quality of life for affected individuals.