We experienced a unique case of familial prion disease with a prion gene mutation that caused pan-autonomic failure, sensory neuropathy and mild cognitive impairment. No abnormal sites of intensity were observed on diffusion-weighted magnetic resonance image (MRI) over six to 11 years or fluid attenuated inversion recovery MRI at six or nine years. However, (99m)Tc-ethylcysteinate dimer single photon emission computed tomography (SPECT) showed a decreased cerebral blood flow in the bilateral parietal and occipital lobes at nine years, which then expanded at 11 years, corresponding to mild atrophy in these areas on MRI. In some cases of prion mutations, particularly the slowly progressive type, SPECT may show abnormalities, while MRI does not.