Primary lateral sclerosis (PLS) is an idiopathic non-familial motor neuron disease characterized by slowly progressive upper motor neuron dysfunction leading to spasticity, mild weakness in voluntary muscle movement, hyperreflexia, and loss of motor speech production. The disease is Monarch Disease Ontology term MONDO_0018155 (lateral sclerosis). Also known as: PLS, adult-onset PLS, adult-onset primary lateral sclerosis, primary lateral sclerosis.