We report clinico-pathological features of a 65-year-old woman and a 56-year-old man with a 5-year clinical history who had clinical and neuropathological characteristics of upper and lower motor neuron disease consistent with amyotrophic lateral sclerosis, and a frontotemporal atrophy pattern in case 2 without TDP-43 pathology. Instead, spongiform change and pathological prion protein deposits were observed in several brain regions. No prion protein gene mutations were found. Western blot analysis showed a five-band profile compatible with variably protease-sensitive prionopathy. We conclude that this disease can display prolonged disease duration and clinico-pathological features within the ALS/FTLD spectrum.