Amyotrophic Lateral Sclerosis

Importance: Amyotrophic lateral sclerosis (ALS) is a neurodegenerative disease characterized by progressive weakness due to degeneration of upper motor neurons in the brain and lower motor neurons in the brainstem and spinal cord. It affects approximately 25 000 individuals in the United States. Observations: Amyotrophic lateral sclerosis is characterized by progressive painless muscle weakness that typically begins in a focal region of the body, such as limb muscle weakness causing hand weakness or foot drop (65%), cranial muscle weakness causing speech or swallowing problems (20%-25%), or axial muscle weakness causing bent posture (5%-10%), and spreads to other body regions over time. The disease usually manifests with dysfunction indicative of both upper motor neurons (causing muscle stiffness and spasticity) and lower motor neurons (causing weakness, fasciculations, atrophy, and flaccidity). After onset, weakness spreads through the musculature and typically causes death due to respiratory muscle weakness. Among people with ALS, approximately 85% have sporadic ALS, which is not associated with known environmental or genetic factors, and 15% have familial ALS. Amyotrophic lateral sclerosis is diagnosed based on clinical features, which can be supported by results of electromyography. More than 60 genes have been associated with ALS, and most are autosomal dominant. Pathogenic variants in chromosome 9 open reading frame 72 (C9orf72) are found in 40% of all familial ALS cases, and pathogenic variants in superoxide dismutase 1 (SOD1) are found in 20% of patients with familial ALS. Patients with ALS survive a mean of 3 to 5 years after diagnosis, and there are currently no curative therapies. Clinical care primarily focuses on symptom management and quality of life. Three US Food and Drug Administration (FDA)-approved disease-modifying therapies are available in the United States. Riluzole and edaravone are oral medications that slow ALS progression by up to 2 to 4 months, and tofersen is an intrathecally administered gene therapy for patients with SOD1 gene variants. Specialized multidisciplinary teams, comprising neurologists, nurses, therapists, dietitians, and social workers, are associated with improved survival (4-7 months) and quality of life. Conclusions and Relevance: Amyotrophic lateral sclerosis is a progressive and fatal neurodegenerative disorder of upper and lower motor neurons. No curative therapies exist. Two oral medications, riluzole and edaravone, are approved by the FDA and modestly decrease disease progression in sporadic ALS. Tofersen, an intrathecally administered gene-based therapy, is also FDA approved and slows disease progression in patients with SOD1 pathogenic gene variants.