Primary lateral sclerosis (PLS) is a sporadic progressive neuromuscular disease caused by upper motor neuron damage. Average age of onset is 40-60 years, and the condition is more common in men than in women. Patients typically present with gradual lower extremity spasticity, hyperreflexia, and weakness, which may be asymmetric at onset. Some may develop gait and balance problems and eventually become wheelchair dependent. Over time, the trunk, upper extremities, and bulbar muscles are involved, leading to arm and hand weakness, dysarthria, and dysphagia. Progression is variable, although there is gradual accumulation of disability. Patients can survive for 20 or more years after symptom onset, and life expectancy may not be shortened.