A 39-year-old man with a history of spastic diplegic CP presented with progressive lower extremity weakness. He was born at term with a delayed initial cry but otherwise normal early development. At age 3, he was diagnosed with CP due to bilateral leg weakness and spasticity. He ambulated independently in childhood with an abnormal gait and remained stable until his late 20s, when gradual worsening of weakness and gait impairment led to walker use and, by age 32, wheelchair dependence.
Neurologic examination revealed marked lower extremity spasticity with diffuse hyperreflexia, consistent with a pure upper motor neuron process. Electromyography and nerve conduction studies were normal. Given the progressive phenotype and lack of clear perinatal injury, genetic testing for HSP was performed, identifying a heterozygous pathogenic SPAST variant. Family history was negative, suggesting a de novo mutation. Baclofen titration was initiated, and genetic counseling with cascade testing was arranged.